Bio

Academic Appointments


Administrative Appointments


  • Professor, Department of Psychology (2003 - Present)
  • Director, Stanford Memory Laboratory (2003 - Present)
  • Co-Director, Stanford Center for Cognitive and Neurobiological Imaging (2010 - Present)

Professional Education


  • PhD, Stanford University, Psychology (Cog Neuroscience) (1997)

Research & Scholarship

Current Research and Scholarly Interests


Cognitive neuroscience of memory and cognitive/executive control in young and older adults. Research interests include encoding and retrieval mechanisms; interactions between declarative, nondeclarative, and working memory; forms of cognitive control; neurocognitive aging; functional organization of prefrontal cortex, parietal cortex, and the medial temporal lobe; assessed by functional MRI, scalp and intracranial EEG, and transcranial magnetic stimulation

Teaching

2013-14 Courses


Graduate and Fellowship Programs


Publications

Journal Articles


  • Global Similarity and Pattern Separation in the Human Medial Temporal Lobe Predict Subsequent Memory JOURNAL OF NEUROSCIENCE LaRocque, K. F., Smith, M. E., Carr, V. A., Witthoft, N., Grill-Spector, K., Wagner, A. D. 2013; 33 (13): 5466-5474

    Abstract

    Intense debate surrounds the role of medial temporal lobe (MTL) structures in recognition memory. Using high-resolution fMRI and analyses of pattern similarity in humans, we examined the encoding computations subserved by MTL subregions. Specifically, we tested the theory that MTL cortex supports memory by encoding overlapping representations, whereas hippocampus supports memory by encoding pattern-separated representations. Consistent with this view, the relationship between encoding pattern similarity and subsequent memory dissociated MTL cortex and hippocampus: later memory was predicted by greater across-item pattern similarity in perirhinal cortex and in parahippocampal cortex, but greater pattern distinctiveness in hippocampus. Additionally, by comparing neural patterns elicited by individual stimuli regardless of subsequent memory, we found that perirhinal cortex and parahippocampal cortex exhibited differential content sensitivity for multiple stimulus categories, whereas hippocampus failed to demonstrate content sensitivity. These data provide novel evidence that complementary MTL encoding computations subserve declarative memory.

    View details for DOI 10.1523/JNEUROSCI.4293-12.2013

    View details for Web of Science ID 000316948600005

    View details for PubMedID 23536062

  • Distributed Representations in Memory: Insights from Functional Brain Imaging ANNUAL REVIEW OF PSYCHOLOGY, VOL 63 Rissman, J., Wagner, A. D. 2012; 63: 101-128

    Abstract

    Forging new memories for facts and events, holding critical details in mind on a moment-to-moment basis, and retrieving knowledge in the service of current goals all depend on a complex interplay between neural ensembles throughout the brain. Over the past decade, researchers have increasingly utilized powerful analytical tools (e.g., multivoxel pattern analysis) to decode the information represented within distributed functional magnetic resonance imaging activity patterns. In this review, we discuss how these methods can sensitively index neural representations of perceptual and semantic content and how leverage on the engagement of distributed representations provides unique insights into distinct aspects of memory-guided behavior. We emphasize that, in addition to characterizing the contents of memories, analyses of distributed patterns shed light on the processes that influence how information is encoded, maintained, or retrieved, and thus inform memory theory. We conclude by highlighting open questions about memory that can be addressed through distributed pattern analyses.

    View details for DOI 10.1146/annurev-psych-120710-100344

    View details for Web of Science ID 000299709900005

    View details for PubMedID 21943171

  • Fidelity of neural reactivation reveals competition between memories PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Kuhl, B. A., Rissman, J., Chun, M. M., Wagner, A. D. 2011; 108 (14): 5903-5908

    Abstract

    Remembering an event from the past is often complicated by the fact that our memories are cluttered with similar events. Though competition is a fundamental part of remembering, there is little evidence of how mnemonic competition is neurally represented. Here, we assessed whether competition between visual memories is captured in the relative degree to which target vs. competing memories are reactivated within the ventral occipitotemporal cortex (VOTC). To assess reactivation, we used multivoxel pattern analysis of fMRI data, quantifying the degree to which retrieval events elicited patterns of neural activity that matched those elicited during encoding. Consistent with recent evidence, we found that retrieval of visual memories was associated with robust VOTC reactivation and that the degree of reactivation scaled with behavioral expressions of target memory retrieval. Critically, competitive remembering was associated with more ambiguous patterns of VOTC reactivation, putatively reflecting simultaneous reactivation of target and competing memories. Indeed, the more weakly that target memories were reactivated, the more likely that competing memories were later remembered. Moreover, when VOTC reactivation indicated that conflict between target and competing memories was high, frontoparietal mechanisms were markedly engaged, revealing specific neural mechanisms that tracked competing mnemonic evidence. Together, these findings provide unique evidence that neural reactivation captures competition between individual memories, providing insight into how well target memories are retrieved in the present and how likely competing memories will be remembered in the future.

    View details for DOI 10.1073/pnas.1016939108

    View details for Web of Science ID 000289265300077

    View details for PubMedID 21436044

  • A Roadmap to Brain Mapping: Toward a Functional Map of Human Parietal Cortex NEURON Uncapher, M. R., Hutchinson, J. B., Wagner, A. D. 2010; 67 (1): 5-8

    Abstract

    In this issue of Neuron, Nelson and colleagues report a novel parcellation of human lateral parietal cortex based on task-induced response profiles and resting-state functional connectivity. Their findings inform current debates about the contributions of parietal cortex to cognition, including the retrieval of episodic memories.

    View details for DOI 10.1016/j.neuron.2010.06.025

    View details for Web of Science ID 000280221000003

    View details for PubMedID 20624586

  • Detecting individual memories through the neural decoding of memory states and past experience PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Rissman, J., Greely, H. T., Wagner, A. D. 2010; 107 (21): 9849-9854

    Abstract

    A wealth of neuroscientific evidence indicates that our brains respond differently to previously encountered than to novel stimuli. There has been an upswell of interest in the prospect that functional MRI (fMRI), when coupled with multivariate data analysis techniques, might allow the presence or absence of individual memories to be detected from brain activity patterns. This could have profound implications for forensic investigations and legal proceedings, and thus the merits and limitations of such an approach are in critical need of empirical evaluation. We conducted two experiments to investigate whether neural signatures of recognition memory can be reliably decoded from fMRI data. In Exp. 1, participants were scanned while making explicit recognition judgments for studied and novel faces. Multivoxel pattern analysis (MVPA) revealed a robust ability to classify whether a given face was subjectively experienced as old or new, as well as whether recognition was accompanied by recollection, strong familiarity, or weak familiarity. Moreover, a participant's subjective mnemonic experiences could be reliably decoded even when the classifier was trained on the brain data from other individuals. In contrast, the ability to classify a face's objective old/new status, when holding subjective status constant, was severely limited. This important boundary condition was further evidenced in Exp. 2, which demonstrated that mnemonic decoding is poor when memory is indirectly (implicitly) probed. Thus, although subjective memory states can be decoded quite accurately under controlled experimental conditions, fMRI has uncertain utility for objectively detecting an individual's past experiences.

    View details for DOI 10.1073/pnas.1001028107

    View details for Web of Science ID 000278054700067

    View details for PubMedID 20457911

  • Resistance to forgetting associated with hippocampus-mediated reactivation during new learning NATURE NEUROSCIENCE Kuhl, B. A., Shah, A. T., DuBrow, S., Wagner, A. D. 2010; 13 (4): 501-U128

    Abstract

    One of the reasons why we forget past experiences is because we acquire new memories in the interim. Although the hippocampus is thought to be important for acquiring and retaining memories, there is little evidence linking neural operations during new learning to the forgetting (or remembering) of earlier events. We found that, during the encoding of new memories, responses in the human hippocampus are predictive of the retention of memories for previously experienced, overlapping events. This brain-behavior relationship is evident in neural responses to individual events and in differences across individuals. We found that the hippocampus accomplishes this function by reactivating older memories as new memories are formed; in this case, reactivating neural responses that represented monetary rewards associated with older memories. These data reveal a fundamental mechanism by which the hippocampus tempers the forgetting of older memories as newer memories are acquired.

    View details for DOI 10.1038/nn.2498

    View details for Web of Science ID 000276073500021

    View details for PubMedID 20190745

  • Imaging the Human Medial Temporal Lobe with High-Resolution fMRI NEURON Carr, V. A., Rissman, J., Wagner, A. D. 2010; 65 (3): 298-308

    Abstract

    High-resolution functional MRI (hr-fMRI) affords unique leverage on the functional properties of human medial temporal lobe (MTL) substructures. We review initial hr-fMRI efforts to delineate (1) encoding and retrieval processes within the hippocampal circuit, (2) hippocampal subfield contributions to pattern separation and pattern completion, and (3) the representational capabilities of distinct MTL subregions. Extant data reveal functional heterogeneity within human MTL and highlight the promise of hr-fMRI for bridging human, animal, and computational approaches to understanding MTL function.

    View details for DOI 10.1016/j.neuron.2009.12.022

    View details for Web of Science ID 000275185200004

    View details for PubMedID 20159444

  • Cognitive control in media multitaskers PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Ophir, E., Nass, C., Wagner, A. D. 2009; 106 (37): 15583-15587

    Abstract

    Chronic media multitasking is quickly becoming ubiquitous, although processing multiple incoming streams of information is considered a challenge for human cognition. A series of experiments addressed whether there are systematic differences in information processing styles between chronically heavy and light media multitaskers. A trait media multitasking index was developed to identify groups of heavy and light media multitaskers. These two groups were then compared along established cognitive control dimensions. Results showed that heavy media multitaskers are more susceptible to interference from irrelevant environmental stimuli and from irrelevant representations in memory. This led to the surprising result that heavy media multitaskers performed worse on a test of task-switching ability, likely due to reduced ability to filter out interference from the irrelevant task set. These results demonstrate that media multitasking, a rapidly growing societal trend, is associated with a distinct approach to fundamental information processing.

    View details for DOI 10.1073/pnas.0903620106

    View details for Web of Science ID 000269806600016

    View details for PubMedID 19706386

  • Integrating Memories in the Human Brain: Hippocampal-Midbrain Encoding of Overlapping Events NEURON Shohamy, D., Wagner, A. D. 2008; 60 (2): 378-389

    Abstract

    Decisions are often guided by generalizing from past experiences. Fundamental questions remain regarding the cognitive and neural mechanisms by which generalization takes place. Prior data suggest that generalization may stem from inference-based processes at the time of generalization. By contrast, generalization may emerge from mnemonic processes occurring while premise events are encoded. Here, participants engaged in a two-phase learning and generalization task, wherein they learned a series of overlapping associations and subsequently generalized what they learned to novel stimulus combinations. Functional MRI revealed that successful generalization was associated with coupled changes in learning-phase activity in the hippocampus and midbrain (ventral tegmental area/substantia nigra). These findings provide evidence for generalization based on integrative encoding, whereby overlapping past events are integrated into a linked mnemonic representation. Hippocampal-midbrain interactions support the dynamic integration of experiences, providing a powerful mechanism for building a rich associative history that extends beyond individual events.

    View details for DOI 10.1016/j.neuron.2008.09.023

    View details for Web of Science ID 000260549300019

    View details for PubMedID 18957228

  • Decreased demands on cognitive control reveal the neural processing benefits of forgetting NATURE NEUROSCIENCE Kuhl, B. A., Dudukovic, N. M., Kahn, I., Wagner, A. D. 2007; 10 (7): 908-914

    Abstract

    Remembering often requires the selection of goal-relevant memories in the face of competition from irrelevant memories. Although there is a cost of selecting target memories over competing memories (increased forgetting of the competing memories), here we report neural evidence for the adaptive benefits of forgetting--namely, reduced demands on cognitive control during future acts of remembering. Functional magnetic resonance imaging during selective retrieval showed that repeated retrieval of target memories was accompanied by dynamic reductions in the engagement of functionally coupled cognitive control mechanisms that detect (anterior cingulate cortex) and resolve (dorsolateral and ventrolateral prefrontal cortex) mnemonic competition. Strikingly, regression analyses revealed that this prefrontal disengagement tracked the extent to which competing memories were forgotten; greater forgetting of competing memories was associated with a greater decline in demands on prefrontal cortex during target remembering. These findings indicate that, although forgetting can be frustrating, memory might be adaptive because forgetting confers neural processing benefits.

    View details for DOI 10.1038/nn1918

    View details for Web of Science ID 000247560200022

    View details for PubMedID 17558403

  • Left ventrolateral prefrontal cortex and the cognitive control of memory NEUROPSYCHOLOGIA Badre, D., Wagner, A. D. 2007; 45 (13): 2883-2901

    Abstract

    Cognitive control mechanisms permit memory to be accessed strategically, and so aid in bringing knowledge to mind that is relevant to current goals and actions. In this review, we consider the contribution of left ventrolateral prefrontal cortex (VLPFC) to the cognitive control of memory. Reviewed evidence supports a two-process model of mnemonic control, supported by a double dissociation among rostral regions of left VLPFC. Specifically, anterior VLPFC (approximately BA 47; inferior frontal gyrus pars orbitalis) supports controlled access to stored conceptual representations, whereas mid-VLPFC (approximately BA 45; inferior frontal gyrus pars triangularis) supports a domain-general selection process that operates post-retrieval to resolve competition among active representations. We discuss the contribution of these control mechanisms across a range of mnemonic domains, including semantic retrieval, recollection of contextual details about past events, resolution of proactive interference in working memory, and task switching. Finally, we consider open directions for future research into left VLPFC function and the cognitive control of memory.

    View details for DOI 10.1016/j.neuropsychologia.2007.06.015

    View details for Web of Science ID 000250257100001

    View details for PubMedID 17675110

  • Computational and neurobiological mechanisms underlying cognitive flexibility PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Badre, D., Wagner, A. D. 2006; 103 (18): 7186-7191

    Abstract

    The ability to switch between multiple tasks is central to flexible behavior. Although switching between tasks is readily accomplished, a well established consequence of task switching (TS) is behavioral slowing. The source of this switch cost and the contribution of cognitive control to its resolution remain highly controversial. Here, we tested whether proactive interference arising from memory places fundamental constraints on flexible performance, and whether prefrontal control processes contribute to overcoming these constraints. Event-related functional MRI indexed neural responses during TS. The contributions of cognitive control and interference were made theoretically explicit in a computational model of task performance. Model estimates of two levels of proactive interference, "conceptual conflict" and "response conflict," produced distinct preparation-related profiles. Left ventrolateral prefrontal cortical activation paralleled model estimates of conceptual conflict, dissociating from that in left inferior parietal cortex, which paralleled model estimates of response conflict. These computationally informed neural measures specify retrieved conceptual representations as a source of conflict during TS and suggest that left ventrolateral prefrontal cortex resolves this conflict to facilitate flexible performance.

    View details for DOI 10.1073/pnas.0509550103

    View details for Web of Science ID 000237399900072

    View details for PubMedID 16632612

  • Dissociable controlled retrieval and generalized selection mechanisms in ventrolateral prefrontal cortex NEURON Badre, D., Poldrack, R. A., Pare-Blagoev, E. J., Insler, R. Z., Wagner, A. D. 2005; 47 (6): 907-918

    Abstract

    How does ventrolateral prefrontal cortex (VLPFC) control mnemonic processing? Alternative models propose that VLPFC guides top-down (controlled) retrieval of knowledge from long-term stores or selects goal-relevant products of retrieval from among competitors. A paucity of evidence supports a retrieval/selection distinction, raising the possibility that these models reduce to a common mechanism. Here, four manipulations varied semantic control demands during fMRI: judgment specificity, cue-target-associative strength, competitor dominance, and number of competitors. Factor analysis revealed evidence for a metafactor that accounted for common behavioral variance across manipulations and for functional variance in left mid-VLPFC. These data support a generalized control process that selects relevant knowledge from among competitors. By contrast, left anterior VLPFC and middle temporal cortex were sensitive to cue-target-associative strength, but not competition, consistent with a control process that retrieves knowledge stored in lateral temporal cortex. Distinct PFC mechanisms mediate top-down retrieval and postretrieval selection.

    View details for DOI 10.1016/j.neuron.2005.07.023

    View details for Web of Science ID 000232085000017

    View details for PubMedID 16157284

  • Parietal lobe contributions to episodic memory retrieval TRENDS IN COGNITIVE SCIENCES Wagner, A. D., Shannon, B. J., Kahn, I., Buckner, R. L. 2005; 9 (9): 445-453

    Abstract

    Although the parietal lobe is not traditionally thought to support declarative memory, recent event-related fMRI studies of episodic retrieval have consistently revealed a range of memory-related influences on activation in lateral posterior parietal cortex (PPC) and precuneus extending into posterior cingulate and retrosplenial cortex. This article surveys the fMRI literature on PPC activation during remembering, a literature that complements earlier electroencephalography data. We consider these recent memory-related fMRI responses within the context of classical ideas about parietal function that emphasize space-based attention and motor intention. We conclude by proposing three hypotheses concerning how parietal cortex might contribute to memory.

    View details for DOI 10.1016/j.tics.2005.07.001

    View details for Web of Science ID 000232251000015

    View details for PubMedID 16054861

  • Memory strength and repetition suppression: Multimodal imaging of medial temporal cortical contributions to recognition NEURON Gonsalves, B. D., Kahn, I., Curran, T., Norman, K. A., Wagner, A. D. 2005; 47 (5): 751-761

    Abstract

    Declarative memory permits an organism to recognize stimuli that have been previously encountered, discriminating them from those that are novel. One basis for recognition is item memory strength, which may support the perception of stimulus familiarity. Though the medial temporal lobes are known to be critical for declarative memory, at present the neural mechanisms supporting perceived differences in memory strength remain poorly specified. Here, functional MRI (fMRI) and anatomically constrained magnetoencephalography (MEG) indexed correlates of graded memory strength in the human brain, focusing on medial temporal cortex. fMRI revealed a decrease in medial temporal cortical activation that tracked parametric levels of perceived memory strength. Anatomically constrained MEG current estimates revealed that strength-dependent signal reductions onset within 150-300 ms. Memory strength appears to be rapidly signaled by medial temporal cortex through repetition suppression (activation reductions), providing a basis for the subjective perception of stimulus familiarity or novelty.

    View details for DOI 10.1016/j.neuron.2005.07.013

    View details for Web of Science ID 000231782700015

    View details for PubMedID 16129403

  • Selection, integration, and conflict monitoring: Assessing the nature and generality of prefrontal cognitive control mechanisms NEURON Badre, D., Wagner, A. D. 2004; 41 (3): 473-487

    Abstract

    Prefrontal cortex (PFC) supports flexible behavior by mediating cognitive control, though the elemental forms of control supported by PFC remain a central debate. Dorsolateral PFC (DLPFC) is thought to guide response selection under conditions of response conflict or, alternatively, may refresh recently active representations within working memory. Lateral frontopolar cortex (FPC) may also adjudicate response conflict, though others propose that FPC supports higher order control processes such as subgoaling and integration. Anterior cingulate cortex (ACC) is hypothesized to upregulate response selection by detecting response conflict; it remains unclear whether ACC functions generalize beyond monitoring response conflict. The present fMRI experiment directly tested these competing theories regarding the functional roles of DLPFC, FPC, and ACC. Results reveal dissociable control processes in PFC, with mid-DLPFC selectively mediating resolution of response conflict and FPC further mediating subgoaling/integration. ACC demonstrated a broad sensitivity to control demands, suggesting a generalized role in modulating cognitive control.

    View details for Web of Science ID 000221457900017

    View details for PubMedID 14766185

  • Multiple routes to memory: Distinct medial temporal lobe processes build item and source memories PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Davachi, L., Mitchell, J. P., Wagner, A. D. 2003; 100 (4): 2157-2162

    Abstract

    A central function of memory is to permit an organism to distinguish between stimuli that have been previously encountered and those that are novel. Although the medial temporal lobe (which includes the hippocampus and surrounding perirhinal, parahippocampal, and entorhinal cortices) is known to be crucial for recognition memory, controversy remains regarding how the specific subregions within the medial temporal lobe contribute to recognition. We used event-related functional MRI to examine the relation between activation in distinct medial temporal lobe subregions during memory formation and the ability (i) to later recognize an item as previously encountered (item recognition) and (ii) to later recollect specific contextual details about the prior encounter (source recollection). Encoding activation in hippocampus and in posterior parahippocampal cortex predicted later source recollection, but was uncorrelated with item recognition. In contrast, encoding activation in perirhinal cortex predicted later item recognition, but not subsequent source recollection. These outcomes suggest that the subregions within the medial temporal lobe subserve distinct, but complementary, learning mechanisms.

    View details for DOI 10.1073/pnas.0337195100

    View details for Web of Science ID 000181073000127

    View details for PubMedID 12578977

  • Executive control during episodic retrieval: Multiple prefrontal processes subserve source memory NEURON Dobbins, I. G., Foley, H., Schacter, D. L., Wagner, A. D. 2002; 35 (5): 989-996

    Abstract

    During recognition, one may sense items as familiar (item memory) and additionally recollect specific contextual details of the earlier encounters (source memory). Cognitive theory suggests that, unlike item memory, source memory requires controlled cue specification and monitoring processes. Functional imaging suggests that such processes may depend on left prefrontal cortex (PFC). However, the nature and possible anatomical segregation of these processes remains unknown. Using functional magnetic resonance imaging, we isolated distinct response patterns in left PFC during source memory consistent with semantic analysis/cue specification (anterior ventrolateral), recollective monitoring (posterior dorsolateral and frontopolar), and phonological maintenance/rehearsal (posterior ventrolateral). Importantly, cue specification and recollective monitoring responses were not seen during item memory and were unaffected by retrieval success, demonstrating that the mere attempt to recollect episodic detail engages multiple control processes with different left PFC substrates.

    View details for Web of Science ID 000177779800019

    View details for PubMedID 12372291

  • Observing the transformation of experience into memory TRENDS IN COGNITIVE SCIENCES Paller, K. A., Wagner, A. D. 2002; 6 (2): 93-102

    Abstract

    The ability to remember one's past depends on neural processing set in motion at the moment each event is experienced. Memory formation can be observed by segregating neural responses according to whether or not each event is recalled or recognized on a subsequent memory test. Subsequent memory analyses have been performed with various neural measures, including brain potentials extracted from intracranial and extracranial electroencephalographic recordings, and hemodynamic responses from functional magnetic resonance imaging. Neural responses can predict which events, and which aspects of those events, will be subsequently remembered or forgotten, thereby elucidating the neurocognitive processes that establish durable episodic memories.

    View details for Web of Science ID 000173740900012

    View details for PubMedID 15866193

  • On the tip of the tongue: An event-related fMRI study of semantic retrieval failure and cognitive conflict NEURON Maril, A., Wagner, A. D., Schacter, D. L. 2001; 31 (4): 653-660

    Abstract

    The tip of the tongue (TOT) state refers to a temporary inaccessibility of information that one is sure exists in long-term memory and is on the verge of recovering. Using event-related fMRI, we assessed the neural correlates of this semantic retrieval failure to determine whether the anterior cingulate-lateral prefrontal neural circuit posited to mediate conflict resolution is engaged during metacognitive conflicts that arise during the TOT. Results revealed that, relative to successful retrieval or unsuccessful retrieval not accompanied by a TOT, retrieval failures accompanied by TOTs elicited a selective response in anterior cingulate-prefrontal cortices. During a TOT, cognitive control mechanisms may be recruited in attempts to resolve the conflict and retrieval failure that characterize this state.

    View details for Web of Science ID 000170759200018

    View details for PubMedID 11545723

  • Recovering meaning: Left prefrontal cortex guides controlled semantic retrieval NEURON Wagner, A. D., Pare-Blagoev, E. J., Clark, J., Poldrack, R. A. 2001; 31 (2): 329-338

    Abstract

    Prefrontal cortex plays a central role in mnemonic control, with left inferior prefrontal cortex (LIPC) mediating control of semantic knowledge. One prominent theory posits that LIPC does not mediate semantic retrieval per se, but rather subserves the selection of task-relevant knowledge from amidst competing knowledge. The present event-related fMRI study provides evidence for an alternative hypothesis: LIPC guides controlled semantic retrieval irrespective of whether retrieval requires selection against competing representations. With selection demands held constant, LIPC activation increased with semantic retrieval demands and with the level of control required during retrieval. LIPC mediates a top-down bias signal that is recruited to the extent that the recovery of meaning demands controlled retrieval. Selection may reflect a specific instantiation of this mechanism.

    View details for Web of Science ID 000170277700016

    View details for PubMedID 11502262

  • Prefrontal-temporal circuitry for episodic encoding and subsequent memory JOURNAL OF NEUROSCIENCE Kirchhoff, B. A., Wagner, A. D., Maril, A., Stern, C. E. 2000; 20 (16): 6173-6180

    Abstract

    Humans encounter and form memories for multiple types of experiences that differ in content, novelty, and memorability. Critical for understanding memory is determining (1) how the brain supports the encoding of events with differing content and (2) whether neural regions that are sensitive to novelty also influence whether stimuli will be subsequently remembered. This event-related functional magnetic resonance imaging (fMRI) study crossed content (picture/word), novelty (novel/repeated), and subsequent memory (remembered/forgotten) to examine prefrontal and temporal lobe contributions to encoding. Results revealed three patterns of encoding-related activation in anatomically connected inferior prefrontal and lateral temporal structures that appeared to vary depending on whether visuospatial/visuo-object, phonological/lexical, or semantic attributes were processed. Event content also modulated medial temporal lobe activity; word encoding predominantly activated the left hemisphere, whereas picture encoding activated both hemispheres. Critically, in prefrontal and temporal regions that were modulated by novelty, the magnitude of encoding activation also predicted whether an event would be subsequently remembered. These results suggest that (1) regions that demonstrate a sensitivity to novelty may actively support encoding processes that impact subsequent explicit memory and (2) multiple content-dependent prefrontal-temporal circuits support event encoding. The similarities between prefrontal and lateral temporal encoding responses raise the possibility that prefrontal modulation of posterior cortical representations is central to encoding.

    View details for Web of Science ID 000088676400034

    View details for PubMedID 10934267

  • Working memory contributions to human learning and remembering NEURON Wagner, A. D. 1999; 22 (1): 19-22

    View details for Web of Science ID 000078410300008

    View details for PubMedID 10027285

  • Building memories: Remembering and forgetting of verbal experiences as predicted by brain activity SCIENCE Wagner, A. D., Schacter, D. L., Rotte, M., Koutstaal, W., Maril, A., Dale, A. M., Rosen, B. R., Buckner, R. L. 1998; 281 (5380): 1188-1191

    Abstract

    A fundamental question about human memory is why some experiences are remembered whereas others are forgotten. Brain activation during word encoding was measured using blocked and event-related functional magnetic resonance imaging to examine how neural activation differs for subsequently remembered and subsequently forgotten experiences. Results revealed that the ability to later remember a verbal experience is predicted by the magnitude of activation in left prefrontal and temporal cortices during that experience. These findings provide direct evidence that left prefrontal and temporal regions jointly promote memory formation for verbalizable events.

    View details for Web of Science ID 000075531200052

    View details for PubMedID 9712582

  • Human hippocampal increases in low-frequency power during associative prediction violations. Neuropsychologia Chen, J., Dastjerdi, M., Foster, B. L., LaRocque, K. F., Rauschecker, A. M., Parvizi, J., Wagner, A. D. 2013; 51 (12): 2344-2351

    Abstract

    Environmental cues often trigger memories of past events (associative retrieval), and these memories are a form of prediction about imminent experience. Learning is driven by the detection of prediction violations, when the past and present diverge. Using intracranial electroencephalography (iEEG), we show that associative prediction violations elicit increased low-frequency power (in the slow-theta range) in human hippocampus, that this low-frequency power increase is modulated by whether conditions allow predictions to be generated, that the increase rapidly onsets after the moment of violation, and that changes in low-frequency power are not present in adjacent perirhinal cortex. These data suggest that associative mismatch is computed within hippocampus when cues trigger predictions that are violated by imminent experience.

    View details for DOI 10.1016/j.neuropsychologia.2013.03.019

    View details for PubMedID 23571081

  • Hippocampal novelty activations in schizophrenia: Disease and medication effects SCHIZOPHRENIA RESEARCH Tamminga, C. A., Thomas, B. P., Chin, R., Mihalakos, P., Youens, K., Wagner, A. D., Preston, A. R. 2012; 138 (2-3): 157-163

    Abstract

    We examined hippocampal activation in schizophrenia (SZ) with fMRI BOLD in response to the presentation of novel and familiar scenes. Voxel-wise analysis showed no group differences. However, anatomical region-of-interest analyses contrasting normal (NL), SZ-on-medication (SZ-ON), SZ-off-medication (SZ-OFF) showed substantial differences in MTL-based novelty responding, accounted for by the reduction in novelty responses in the SZ-OFF predominantly in the anterior hippocampus and parahippocampal cortex. These differences in novelty-based activation in the SZ-OFF group represent disease characteristics of schizophrenia without confounding effects of antipsychotic medication and illustrate the tendency of antipsychotic drug treatment to improve memory functions in schizophrenia.

    View details for DOI 10.1016/j.schres.2012.03.019

    View details for Web of Science ID 000305279400008

    View details for PubMedID 22480957

  • Multi-voxel patterns of visual category representation during episodic encoding are predictive of subsequent memory NEUROPSYCHOLOGIA Kuhl, B. A., Rissman, J., Wagner, A. D. 2012; 50 (4): 458-469

    Abstract

    Successful encoding of episodic memories is thought to depend on contributions from prefrontal and temporal lobe structures. Neural processes that contribute to successful encoding have been extensively explored through univariate analyses of neuroimaging data that compare mean activity levels elicited during the encoding of events that are subsequently remembered vs. those subsequently forgotten. Here, we applied pattern classification to fMRI data to assess the degree to which distributed patterns of activity within prefrontal and temporal lobe structures elicited during the encoding of word-image pairs were diagnostic of the visual category (Face or Scene) of the encoded image. We then assessed whether representation of category information was predictive of subsequent memory. Classification analyses indicated that temporal lobe structures contained information robustly diagnostic of visual category. Information in prefrontal cortex was less diagnostic of visual category, but was nonetheless associated with highly reliable classifier-based evidence for category representation. Critically, trials associated with greater classifier-based estimates of category representation in temporal and prefrontal regions were associated with a higher probability of subsequent remembering. Finally, consideration of trial-by-trial variance in classifier-based measures of category representation revealed positive correlations between prefrontal and temporal lobe representations, with the strength of these correlations varying as a function of the category of image being encoded. Together, these results indicate that multi-voxel representations of encoded information can provide unique insights into how visual experiences are transformed into episodic memories.

    View details for DOI 10.1016/j.neuropsychologia.2011.09.002

    View details for Web of Science ID 000301898200003

    View details for PubMedID 21925190

  • Dissociable Effects of Top-Down and Bottom-Up Attention during Episodic Encoding JOURNAL OF NEUROSCIENCE Uncapher, M. R., Hutchinson, J. B., Wagner, A. D. 2011; 31 (35): 12613-12628

    Abstract

    It is well established that the formation of memories for life's experiences-episodic memory-is influenced by how we attend to those experiences, yet the neural mechanisms by which attention shapes episodic encoding are still unclear. We investigated how top-down and bottom-up attention contribute to memory encoding of visual objects in humans by manipulating both types of attention during fMRI of episodic memory formation. We show that dorsal parietal cortex-specifically, intraparietal sulcus (IPS)-was engaged during top-down attention and was also recruited during the successful formation of episodic memories. By contrast, bottom-up attention engaged ventral parietal cortex-specifically, temporoparietal junction (TPJ)-and was also more active during encoding failure. Functional connectivity analyses revealed further dissociations in how top-down and bottom-up attention influenced encoding: while both IPS and TPJ influenced activity in perceptual cortices thought to represent the information being encoded (fusiform/lateral occipital cortex), they each exerted opposite effects on memory encoding. Specifically, during a preparatory period preceding stimulus presentation, a stronger drive from IPS was associated with a higher likelihood that the subsequently attended stimulus would be encoded. By contrast, during stimulus processing, stronger connectivity with TPJ was associated with a lower likelihood the stimulus would be successfully encoded. These findings suggest that during encoding of visual objects into episodic memory, top-down and bottom-up attention can have opposite influences on perceptual areas that subserve visual object representation, suggesting that one manner in which attention modulates memory is by altering the perceptual processing of to-be-encoded stimuli.

    View details for DOI 10.1523/JNEUROSCI.0152-11.2011

    View details for Web of Science ID 000294451900024

    View details for PubMedID 21880922

  • Associative retrieval processes in the human medial temporal lobe: Hippocampal retrieval success and CA1 mismatch detection LEARNING & MEMORY Chen, J., Olsen, R. K., Preston, A. R., Glover, G. H., Wagner, A. D. 2011; 18 (8): 523-528

    Abstract

    Hippocampal subfields CA(3) and CA(1) are hypothesized to differentially support the generation of associative predictions and the detection of associative mismatches, respectively. Using high-resolution functional MRI, we examined hippocampal subfield activation during associative retrieval and during subsequent comparisons of memory to matching or mismatching decision probes. Activity in the dentate gyrus/CA(2/3), CA(1), and other medial temporal lobe subregions tracked associative retrieval success, whereas activity in CA(1) and the perirhinal cortex tracked the presence of associative mismatches. These data support the hypothesis that CA(1) acts as a "comparator," detecting when memory for the past and sensory input in the present diverge.

    View details for DOI 10.1101/lm.2135211

    View details for Web of Science ID 000293858000004

    View details for PubMedID 21775513

  • Reduced hippocampal activity during encoding in cognitively normal adults carrying the APOE epsilon 4 allele NEUROPSYCHOLOGIA Adamson, M. M., Hutchinson, J. B., Shelton, A. L., Wagner, A. D., Taylor, J. L. 2011; 49 (9): 2448-2455

    Abstract

    Apolipoprotein (APOE) ?4-related differences in memory performance have been detected before age 65. The hippocampus and the surrounding medial temporal lobe (MTL) structures are the first site affected by Alzheimer's disease (AD) and the MTL is the seat of episodic memory, including visuo-spatial memory. While reports of APOE ?4-related differences in these brain structures are not consistent in either cross-sectional or longitudinal structural and functional magnetic resonance imaging (fMRI) studies, there is increasing evidence that brain activity at baseline (defined as activity during fixation or rest) may differ in APOE ?4 carriers compared to non-carriers. In this fMRI study, cognitively normal APOE ?4 carriers and non-carriers engaged in a perspective-dependent spatial learning task (Shelton & Gabrieli, 2002) previously shown to activate MTL structures in older participants (Borghesani et al., 2008). A low-level, visually engaging dot-control task was used for comparison, in addition to fixation. APOE ?4 carriers showed less activation than non-carriers in the hippocampus proper during encoding. Specifically, when spatial encoding was contrasted against the dot-control task, encoding-related activation was significantly lower in carriers than non-carriers. By contrast, no ?4-related differences in the hippocampus were found when spatial encoding was compared with fixation. Lower activation, however, was not global since encoding-related activation in early visual cortex (left lingual gyrus) was not different between APOE ?4 carriers and non-carriers. The present data document APOE ?4-related differences in the hippocampus proper during encoding and underscore the role of low-level control contrasts for complex encoding tasks. These results have implications for fMRI studies that investigate the default-mode network (DMN) in middle-aged to older APOE ?4 carriers to help evaluate AD risk in this otherwise cognitively normal population.

    View details for DOI 10.1016/j.neuropsychologia.2011.04.022

    View details for Web of Science ID 000293611600018

    View details for PubMedID 21549723

  • Expected value information improves financial risk taking across the adult life span SOCIAL COGNITIVE AND AFFECTIVE NEUROSCIENCE Samanez-Larkin, G. R., Wagner, A. D., Knutson, B. 2011; 6 (2): 207-217

    Abstract

    When making decisions, individuals must often compensate for cognitive limitations, particularly in the face of advanced age. Recent findings suggest that age-related variability in striatal activity may increase financial risk-taking mistakes in older adults. In two studies, we sought to further characterize neural contributions to optimal financial risk taking and to determine whether decision aids could improve financial risk taking. In Study 1, neuroimaging analyses revealed that individuals whose mesolimbic activation correlated with the expected value estimates of a rational actor made more optimal financial decisions. In Study 2, presentation of expected value information improved decision making in both younger and older adults, but the addition of a distracting secondary task had little impact on decision quality. Remarkably, provision of expected value information improved the performance of older adults to match that of younger adults at baseline. These findings are consistent with the notion that mesolimbic circuits play a critical role in optimal choice, and imply that providing simplified information about expected value may improve financial risk taking across the adult life span.

    View details for DOI 10.1093/scan/nsq043

    View details for Web of Science ID 000291543100006

    View details for PubMedID 20501485

  • High-resolution fMRI Reveals Match Enhancement and Attentional Modulation in the Human Medial Temporal Lobe JOURNAL OF COGNITIVE NEUROSCIENCE Dudukovic, N. M., Preston, A. R., Archie, J. J., Glover, G. H., Wagner, A. D. 2011; 23 (3): 670-682

    Abstract

    A primary function of the medial temporal lobe (MTL) is to signal prior encounter with behaviorally relevant stimuli. MTL match enhancement--increased activation when viewing previously encountered stimuli--has been observed for goal-relevant stimuli in nonhuman primates during delayed-match-to-sample tasks and in humans during more complex relational memory tasks. Match enhancement may alternatively reflect (a) an attentional response to familiar relative to novel stimuli or (b) the retrieval of contextual details surrounding the past encounter with familiar stimuli. To gain leverage on the functional significance of match enhancement in the hippocampus, high-resolution fMRI of human MTL was conducted while participants attended, ignored, or passively viewed face and scene stimuli in the context of a modified delayed-match-to-sample task. On each "attended" trial, two goal-relevant stimuli were encountered before a probe that either matched or mismatched one of the attended stimuli, enabling examination of the consequences of encountering one of the goal-relevant stimuli as a match probe on later memory for the other (nonprobed) goal-relevant stimulus. fMRI revealed that the hippocampus was insensitive to the attentional manipulation, whereas parahippocampal cortex was modulated by scene-directed attention, and perirhinal cortex showed more subtle and general effects of attention. By contrast, all hippocampal subfields demonstrated match enhancement to the probe, and a postscan test revealed more accurate recognition memory for the nonprobed goal-relevant stimulus on match relative to mismatch trials. These data suggest that match enhancement in human hippocampus reflects retrieval of other goal-relevant contextual details surrounding a stimulus's prior encounter.

    View details for Web of Science ID 000285160700014

    View details for PubMedID 20433244

  • Cognitive control and right ventrolateral prefrontal cortex: reflexive reorienting, motor inhibition, and action updating YEAR IN COGNITIVE NEUROSCIENCE Levy, B. J., Wagner, A. D. 2011; 1224: 40-62

    Abstract

    Delineating the functional organization of the prefrontal cortex is central to advancing models of goal-directed cognition. Considerable evidence indicates that specific forms of cognitive control are associated with distinct subregions of the left ventrolateral prefrontal cortex (VLPFC), but less is known about functional specialization within the right VLPFC. We report a functional MRI meta-analysis of two prominent theories of right VLPFC function: stopping of motor responses and reflexive orienting to abrupt perceptual onsets. Along with a broader review of right VLPFC function, extant data indicate that stopping and reflexive orienting similarly recruit the inferior frontal junction (IFJ), suggesting that IFJ supports the detection of behaviorally relevant stimuli. By contrast, other right VLPFC subregions are consistently active during motor inhibition, but not reflexive reorienting tasks, with posterior-VLPFC being active during the updating of action plans and mid-VLPFC responding to decision uncertainty. These results highlight the rich functional heterogeneity that exists within right VLPFC.

    View details for DOI 10.1111/j.1749-6632.2011.05958.x

    View details for Web of Science ID 000290238100004

    View details for PubMedID 21486295

  • The Hippocampal Formation in Schizophrenia AMERICAN JOURNAL OF PSYCHIATRY Tamminga, C. A., Stan, A. D., Wagner, A. D. 2010; 167 (10): 1178-1193

    Abstract

    The hippocampal formation is one of the most extensively studied regions of the brain, with well-described anatomy and basic physiology; moreover, aspects of human memory mediated by the hippocampus are well characterized. In schizophrenia, alterations in hippocampal anatomy, perfusion, and activation are consistently reported; impairments in declarative memory function, especially in the flexible use of event memories (e.g., in the service of memory-based inference), are common. Postmortem molecular changes suggest a selective reduction in glutamate transmission in the dentate gyrus and in its efferent fibers, the mossy fiber pathway. A reduction in dentate gyrus glutamatergic output and in its information processing functions could generate two co-occurring outcomes in the hippocampus: 1) a change in homeostatic plasticity processes in cornu ammonis 3 (CA3), accompanied by increased activity due to reduced afferent stimulation from the dentate gyrus onto CA3 neurons, a process that could increase the pattern completion functions of CA3, and 2) the loss of mnemonic functions specific to the dentate gyrus, namely pattern separation, a change that could increase the prevalence of illusory pattern completion and reduce discrimination between present and past experiences in memory. The resulting increase in "runaway" CA3-mediated pattern completion could result in cognitive "mistakes," generating psychotic associations and resulting in memories with psychotic content. Tests of this model could result in novel approaches to the treatment of psychosis and declarative memory alterations and in novel animal preparations for basic schizophrenia research.

    View details for DOI 10.1176/appi.ajp.2010.09081187

    View details for Web of Science ID 000282374700010

    View details for PubMedID 20810471

  • Multiple Forms of Learning Yield Temporally Distinct Electrophysiological Repetition Effects CEREBRAL CORTEX Race, E. A., Badre, D., Wagner, A. D. 2010; 20 (7): 1726-1738

    Abstract

    Prior experience with a stimulus leads to multiple forms of learning that facilitate subsequent behavior (repetition priming) and neural processing (repetition suppression). Learning can occur at the level of stimulus-specific features (stimulus learning), associations between stimuli and selected decisions (stimulus-decision learning), and associations between stimuli and selected responses (stimulus-response learning). Although recent functional magnetic resonance imaging results suggest that these distinct forms of learning are associated with repetition suppression (neural priming) in dissociable regions of frontal and temporal cortex, a critical question is how these different forms of learning influence cortical response dynamics. Here, electroencephalography (EEG) measured the temporal structure of neural responses when participants classified novel and repeated stimuli, using a design that isolated the effects of distinct levels of learning. Event-related potential and spectral EEG analyses revealed electrophysiological effects due to stimulus, stimulus-decision, and stimulus-response learning, demonstrating experience-dependent cortical modulation at multiple levels of representation. Stimulus-level learning modulated cortical dynamics earlier in the temporal-processing stream relative to stimulus-decision and stimulus-response learning. These findings indicate that repeated stimulus processing, including the mapping of stimuli to decisions and actions, is influenced by stimulus-level and associative learning mechanisms that yield multiple forms of experience-dependent cortical plasticity.

    View details for DOI 10.1093/cercor/bhp233

    View details for Web of Science ID 000278690800020

    View details for PubMedID 19915094

  • Learning and Generalization in Schizophrenia: Effects of Disease and Antipsychotic Drug Treatment BIOLOGICAL PSYCHIATRY Shohamy, D., Mihalakos, P., Chin, R., Thomas, B., Wagner, A. D., Tamminga, C. 2010; 67 (10): 926-932

    Abstract

    Schizophrenia involves alterations in hippocampal function. The implications of these alterations for memory function in the illness remain poorly understood. Furthermore, it remains unknown how memory is impacted by drug treatments for schizophrenia. The goal of this study was to delineate specific memory processes that are disrupted in schizophrenia and explore how they are affected by medication. We specifically focus on memory generalization--the ability to flexibly generalize memories in novel situations.Individuals with schizophrenia (n = 56) and healthy control subjects (n = 20) were tested on a computerized memory generalization paradigm. Participants first engaged in trial-by-error associative learning. They were then asked to generalize what they learned by responding to novel stimulus combinations. Individuals with schizophrenia were tested on or off antipsychotic medication, using a between-subject design in order to eliminate concerns about learning-set effects.Individuals with schizophrenia were selectively impaired in their ability to generalize knowledge, despite having intact learning and memory accuracy. This impairment was found only in individuals tested off medication. Individuals tested on medication generalized almost as well as healthy control subjects. This between-group difference was selective to memory generalization.These findings suggest that individuals with schizophrenia have a selective alteration in the ability to flexibly generalize past experience toward novel learning environments. This alteration is unaccompanied by global memory impairments. Additionally, the results indicate a robust generalization difference on the basis of medication status. These results suggest that hippocampal abnormalities in schizophrenia might be alleviated with antipsychotic medication, with important implications for understanding adaptive memory-guided behavior.

    View details for DOI 10.1016/j.biopsych.2009.10.025

    View details for Web of Science ID 000277629900005

    View details for PubMedID 20034612

  • High-resolution fMRI of Content-sensitive Subsequent Memory Responses in Human Medial Temporal Lobe JOURNAL OF COGNITIVE NEUROSCIENCE Preston, A. R., Bornstein, A. M., Hutchinson, J. B., Gaare, M. E., Glover, G. H., Wagner, A. D. 2010; 22 (1): 156-173

    Abstract

    The essential role of the medial temporal lobe (MTL) in long-term memory for individual events is well established, yet important questions remain regarding the mnemonic functions of the component structures that constitute the region. Within the hippocampus, recent functional neuroimaging findings suggest that formation of new memories depends on the dentate gyrus and the CA(3) field, whereas the contribution of the subiculum may be limited to retrieval. During encoding, it has been further hypothesized that structures within MTL cortex contribute to encoding in a content-sensitive manner, whereas hippocampal structures may contribute to encoding in a more domain-general manner. In the current experiment, high-resolution fMRI techniques were utilized to assess novelty and subsequent memory effects in MTL subregions for two classes of stimuli--faces and scenes. During scanning, participants performed an incidental encoding (target detection) task with novel and repeated faces and scenes. Subsequent recognition memory was indexed for the novel stimuli encountered during scanning. Analyses revealed voxels sensitive to both novel faces and novel scenes in all MTL regions. However, similar percentages of voxels were sensitive to novel faces and scenes in perirhinal cortex, entorhinal cortex, and a combined region comprising the dentate gyrus, CA(2), and CA(3), whereas parahippocampal cortex, CA(1), and subiculum demonstrated greater sensitivity to novel scene stimuli. Paralleling these findings, subsequent memory effects in perirhinal cortex were observed for both faces and scenes, with the magnitude of encoding activation being related to later memory strength, as indexed by a graded response tracking recognition confidence, whereas subsequent memory effects were scene-selective in parahippocampal cortex. Within the hippocampus, encoding activation in the subiculum correlated with subsequent memory for both stimulus classes, with the magnitude of encoding activation varying in a graded manner with later memory strength. Collectively, these findings suggest a gradient of content sensitivity from posterior (parahippocampal) to anterior (perirhinal) MTL cortex, with MTL cortical regions differentially contributing to successful encoding based on event content. In contrast to recent suggestions, the present data further indicate that the subiculum may contribute to successful encoding irrespective of event content.

    View details for Web of Science ID 000272352100012

    View details for PubMedID 19199423

  • Attention during memory retrieval enhances future remembering MEMORY & COGNITION Dudukovic, N. M., DuBrow, S., Wagner, A. D. 2009; 37 (7): 953-961

    Abstract

    Memory retrieval is a powerful learning event that influences whether an experience will be remembered in the future. Although retrieval can succeed in the presence of distraction, dividing attention during retrieval may reduce the power of remembering as an encoding event. In the present experiments, participants studied pictures of objects under full attention and then engaged in item recognition and source memory retrieval under full or divided attention. Two days later, a second recognition and source recollection test assessed the impact of attention during initial retrieval on long-term retention. On this latter test, performance was superior for items that had been tested initially under full versus divided attention. More importantly, even when items were correctly recognized on the first test, divided attention reduced the likelihood of subsequent recognition on the second test. The same held true for source recollection. Additionally, foils presented during the first test were also less likely to be later recognized if they had been encountered initially under divided attention. These findings demonstrate that attentive retrieval is critical for learning through remembering.

    View details for DOI 10.3758/MC.37.7.953

    View details for Web of Science ID 000270516700002

    View details for PubMedID 19744935

  • Performance-Related Sustained and Anticipatory Activity in Human Medial Temporal Lobe during Delayed Match-to-Sample JOURNAL OF NEUROSCIENCE Olsen, R. K., Nichols, E. A., Chen, J., Hunt, J. F., Glover, G. H., Gabrieli, J. D., Wagner, A. D. 2009; 29 (38): 11880-11890

    Abstract

    The medial temporal lobe (MTL)-hippocampus and surrounding perirhinal, parahippocampal, and entorhinal cortical areas-has long been known to be critical for long-term memory for events. Recent functional neuroimaging and neuropsychological data in humans performing short-delay tasks suggest that the MTL also contributes to performance even when retention intervals are brief, and single-unit data in rodents reveal sustained, performance-related delay activity in the MTL during delayed-non-match-to-sample tasks. The current study used functional magnetic resonance imaging to examine the relationship between activation in human MTL subregions and performance during a delayed-match-to-sample task with repeated (non-trial-unique) stimuli. On critical trials, the presentation of two faces was followed by a 30 s delay period, after which participants performed two-alternative forced-choice recognition. Functional magnetic resonance imaging revealed significant delay period activity in anterior hippocampus, entorhinal cortex, and perirhinal cortex over the 30 s retention interval, with the magnitude of activity being significantly higher on subsequently correct compared with subsequently incorrect trials. In contrast, posterior hippocampus, parahippocampal cortex, and fusiform gyrus activity linearly increased across the 30 s delay, suggesting an anticipatory response, and activity in parahippocampal cortex and hippocampus was greater during the probe period on correct compared with incorrect trials. These results indicate that at least two patterns of MTL delay period activation-sustained and anticipatory-are present during performance of short-delay recognition memory tasks, providing novel evidence that multiple processes govern task performance. Implications for understanding the role of the hippocampus and surrounding MTL cortical areas in recognition memory after short delays are discussed.

    View details for DOI 10.1523/JNEUROSCI.2245-09.2009

    View details for Web of Science ID 000270102000018

    View details for PubMedID 19776274

  • It's In My Eyes, but It Doesn't Look that Way to Me NEURON Kumaran, D., Wagner, A. D. 2009; 63 (5): 561-563

    Abstract

    In this issue of Neuron, Hannula and Ranganath provide striking evidence that hippocampal activity predicts eye movements that reveal memory for the past even when participants' overt memory decisions are in error. Their findings bear on an ongoing debate about the relationship between mnemonic awareness and hippocampal function.

    View details for DOI 10.1016/j.neuron.2009.08.027

    View details for Web of Science ID 000269852300002

    View details for PubMedID 19755098

  • Neural Priming in Human Frontal Cortex: Multiple Forms of Learning Reduce Demands on the Prefrontal Executive System JOURNAL OF COGNITIVE NEUROSCIENCE Race, E. A., Shanker, S., Wagner, A. D. 2009; 21 (9): 1766-1781

    Abstract

    Past experience is hypothesized to reduce computational demands in PFC by providing bottom-up predictive information that informs subsequent stimulus-action mapping. The present fMRI study measured cortical activity reductions ("neural priming"/"repetition suppression") during repeated stimulus classification to investigate the mechanisms through which learning from the past decreases demands on the prefrontal executive system. Manipulation of learning at three levels of representation-stimulus, decision, and response-revealed dissociable neural priming effects in distinct frontotemporal regions, supporting a multiprocess model of neural priming. Critically, three distinct patterns of neural priming were identified in lateral frontal cortex, indicating that frontal computational demands are reduced by three forms of learning: (a) cortical tuning of stimulus-specific representations, (b) retrieval of learned stimulus-decision mappings, and (c) retrieval of learned stimulus-response mappings. The topographic distribution of these neural priming effects suggests a rostrocaudal organization of executive function in lateral frontal cortex.

    View details for Web of Science ID 000270740200010

    View details for PubMedID 18823245

  • Posterior parietal cortex and episodic retrieval: Convergent and divergent effects of attention and memory LEARNING & MEMORY Hutchinson, J. B., Uncapher, M. R., Wagner, A. D. 2009; 16 (6): 343-356

    Abstract

    Functional neuroimaging studies of humans engaged in retrieval from episodic memory have revealed a surprisingly consistent pattern of retrieval-related activity in lateral posterior parietal cortex (PPC). Given the well-established role of lateral PPC in subserving goal-directed and reflexive attention, it has been hypothesized that PPC activation during retrieval reflects the recruitment of parietal attention mechanisms during remembering. Here, we evaluate this hypothesis by considering the anatomical overlap of retrieval and attention effects in lateral PPC. We begin by briefly reviewing the literature implicating dorsal PPC in goal-directed attention and ventral PPC in reflexive attention. We then discuss the pattern of dorsal and ventral PPC activation during episodic retrieval, and conclude with consideration of the degree of anatomical convergence across the two domains. This assessment revealed that predominantly divergent subregions of lateral PPC are engaged during acts of episodic retrieval and during goal-directed and reflexive attention, suggesting that PPC retrieval effects reflect functionally distinct mechanisms from these forms of attention. Although attention must play a role in aspects of retrieval, the data reviewed here suggest that further investigation into the relationship between processes of attention and memory, as well as alternative accounts of PPC contributions to retrieval, is warranted.

    View details for DOI 10.1101/lm.919109

    View details for Web of Science ID 000266565400001

    View details for PubMedID 19470649

  • Integrative Encoding AMERICAN JOURNAL OF PSYCHIATRY Shohamy, D., Wagner, A. D. 2009; 166 (3): 284-284
  • Posterior parietal cortex and episodic encoding: Insights from fMRI subsequent memory effects and dual-attention theory NEUROBIOLOGY OF LEARNING AND MEMORY Uncapher, M. R., Wagner, A. D. 2009; 91 (2): 139-154

    Abstract

    The formation of episodic memories--memories for life events--is affected by attention during event processing. A leading neurobiological model of attention posits two separate yet interacting systems that depend on distinct regions in lateral posterior parietal cortex (PPC). From this dual-attention perspective, dorsal PPC is thought to support the goal-directed allocation of attention, whereas ventral PPC is thought to support reflexive orienting to information that automatically captures attention. To advance understanding of how parietal mechanisms may impact event encoding, we review functional MRI studies that document the relationship between lateral PPC activation during encoding and subsequent memory performance (e.g., later remembering or forgetting). This review reveals that (a) encoding-related activity is frequently observed in human lateral PPC, (b) increased activation in dorsal PPC is associated with later memory success, and (c) increased activation in ventral PPC predominantly correlates with later memory failure. From a dual-attention perspective, these findings suggest that allocating goal-directed attention during event processing increases the probability that the event will be remembered later, whereas the capture of reflexive attention during event processing may have negative consequences for event encoding. The prevalence of encoding-related activation in parietal cortex suggests that neurobiological models of episodic memory should consider how parietal-mediated attentional mechanisms regulate encoding.

    View details for DOI 10.1016/j.nlm.2008.10.011

    View details for Web of Science ID 000263608600006

    View details for PubMedID 19028591

  • CNTRICS Final Task Selection: Long-Term Memory SCHIZOPHRENIA BULLETIN Ragland, J. D., Cools, R., Frank, M., Pizzagalli, D. A., Preston, A., Ranganath, C., Wagner, A. D. 2009; 35 (1): 197-212

    Abstract

    Long-term memory (LTM) is a multifactorial construct, composed of different stages of information processing and different cognitive operations that are mediated by distinct neural systems, some of which may be more responsible for the marked memory problems that limit the daily function of individuals with schizophrenia. From the outset of the CNTRICS initiative, this multidimensionality was appreciated, and an effort was made to identify the specific memory constructs and task paradigms that hold the most promise for immediate translational development. During the second CNTRICS meeting, the LTM group identified item encoding and retrieval and relational encoding and retrieval as key constructs. This article describes the process that the LTM group went through in the third and final CNTRICS meeting to select nominated tasks within the 2 LTM constructs and within a reinforcement learning construct that were judged most promising for immediate development. This discussion is followed by each nominating authors' description of their selected task paradigm, ending with some thoughts about future directions.

    View details for DOI 10.1093/schbul/sbn134

    View details for Web of Science ID 000261682700020

    View details for PubMedID 18927344

  • Overcoming suppression in order to remember: Contributions from anterior cingulate and ventrolateral prefrontal cortex COGNITIVE AFFECTIVE & BEHAVIORAL NEUROSCIENCE Kuhl, B. A., Kahn, I., Dudukovic, N. M., Wagner, A. D. 2008; 8 (2): 211-221

    Abstract

    The ability to remember is often compromised by competition from irrelevant memories. However, acts of selective remembering can alter the competitive relationship between memories; memories that are selected against are weakened, whereas those that are retrieved are strengthened. Whereas the weakening of selected-against memories is typically evidenced by subsequently poorer recall of these memories, the present study tested the hypothesis that when previously selected-against memories can subsequently be successfully retrieved, such acts of successful retrieval are associated with engagement of neurobiological mechanisms that serve to detect and overcome competition. Consistent with this hypothesis, fMRI revealed that anteriorcingulate cortex and right ventrolateral prefrontal cortex are differentially engaged during successful retrieval of previously selected-against memories, and that their engagement is directly related to the magnitude of weakening that is induced by prior acts of selecting against these memories.

    View details for DOI 10.3758/CABN.8.2.211

    View details for Web of Science ID 000257221500009

    View details for PubMedID 18589510

  • Goal-dependent modulation of declarative memory: Neural correlates of temporal recency decisions and novelty detection NEUROPSYCHOLOGIA Dudukovic, N. M., Wagner, A. D. 2007; 45 (11): 2608-2620

    Abstract

    Declarative memory allows an organism to discriminate between previously encountered and novel items, and to place past encounters in time. Numerous imaging studies have investigated the neural processes supporting item recognition, whereas few have examined retrieval of temporal information. In the present study, functional magnetic resonance imaging (fMRI) was conducted while subjects engaged in temporal recency and item novelty decisions. Subjects encountered three-alternative forced-choice retrieval trials, each consisting of two words from a preceding study phase and one novel word, and were instructed to either identify the novel item (Novelty trials) or the more recently presented study item (Recency trials). Relative to correct Novelty decisions, correct Recency decisions elicited greater activation in a network of left-lateralized regions, including frontopolar and dorsolateral prefrontal cortex and intraparietal sulcus. A conjunction analysis revealed that these left-lateralized regions overlapped with those previously observed to be engaged during source recollection versus novelty detection, suggesting that during Recency trials subjects attempted to recollect event details. Consistent with this interpretation, correct Recency decisions activated posterior hippocampus and parahippocampal cortex, whereas incorrect Recency decisions elicited greater anterior cingulate activation. The magnitude of this latter effect positively correlated with activation in right dorsolateral prefrontal cortex. Finally, correct Novelty decisions activated the anterior medial temporal lobe to a greater extent than did correct Recency decisions, suggesting that medial temporal novelty responses are not obligatory but rather can be modulated by the goal-directed allocation of attention. Collectively, these findings advance understanding of how subjects strategically engage frontal and parietal mechanisms in the service of attempting to remember the temporal order of events, and how retrieval goals impact novelty processing within the medial temporal lobe.

    View details for DOI 10.1016/j.neuropsychologia.2007.02.025

    View details for Web of Science ID 000247865800021

    View details for PubMedID 17499318

  • Attending to remember and remembering to attend NEURON Duclukovic, N. M., Wagner, A. D. 2006; 49 (6): 784-787

    Abstract

    Attention and memory are intimately linked. Two functional imaging studies in this issue of Neuron provide novel evidence for this powerful, reciprocal relationship. Turk-Browne and colleagues report that attention simultaneously facilitates the formation of both implicit and explicit memories, while Summerfield and colleagues demonstrate that memory for the past can guide the allocation of attention in the present. Together, these elegant studies reveal bidirectional interactions between attention and memory.

    View details for DOI 10.1016/j.neuron.2006.03.008

    View details for Web of Science ID 000236227500005

    View details for PubMedID 16543125

  • Frontal lobe mechanisms that resolve proactive interference CEREBRAL CORTEX Badre, D., Wagner, A. D. 2005; 15 (12): 2003-2012

    Abstract

    Memory of a past experience can interfere with processing during a subsequent experience, a phenomenon termed proactive interference (PI). Neuroimaging and neuropsychological evidence implicate the left mid-ventrolateral prefrontal cortex (mid-VLPFC) in PI resolution during short-term item recognition, though the precise mechanisms await specification. The present functional magnetic resonance imaging (fMRI) experiment sought to further constrain theorizing regarding PI resolution. On each trial, subjects maintained a target set of words, and then decided if a subsequent probe was contained in the target set (positive) or not (negative). Importantly, for half of the negative and half of the positive trials, the probe had been contained in the previous target set (recent). Relative to non-recent trials, negative-recent trials produced an increase in response times and error rates, behavioral markers of PI. In fMRI measures, negative recency was associated with increased activation in the left mid-VLPFC, as well as in the bilateral fronto-polar cortex, providing evidence for multiple components in PI resolution. Furthermore, recency effects were evident during both negative and positive trials, with the magnitude of the recency effect in the mid-VLPFC being greater on negative trials. Collectively, these results serve to specify and constrain proposed models of PI resolution.

    View details for DOI 10.1093/cercor/bhi075

    View details for Web of Science ID 000233217300014

    View details for PubMedID 15788702

  • Domain-general and domain-sensitive prefrontal mechanisms for recollecting events and detecting novelty CEREBRAL CORTEX Dobbins, I. G., Wagner, A. D. 2005; 15 (11): 1768-1778

    Abstract

    Recollecting the past and discriminating novel from familiar memoranda depend on poorly understood prefrontal cortical (PFC) mechanisms hypothesized to vary according to memory task (e.g. recollection versus novelty detection) and domain of targeted memories (e.g. perceptual versus conceptual). Using event-related fMRI, we demonstrate that recollecting conceptual or perceptual details surrounding object encounters similarly recruits left frontopolar and posterior PFC compared with detecting novel stimuli, suggesting that a domain-general control network is engaged during contextual remembering. In contrast, left anterior ventrolateral PFC coactivated with a left middle temporal region associated with semantic representation, and right ventrolateral PFC with bilateral occipito-temporal cortices associated with representing object form, depending on whether recollections were conceptual or perceptual. These PFC/posterior cortical dissociations suggest that during recollection, lateralized ventrolateral PFC mechanisms bias posterior conceptual or perceptual feature representations as a function of memory relevance, potentially improving the gain of bottom-up memory signals. Supporting this domain-sensitive biasing hypothesis, novelty detection also recruited right ventrolateral PFC and bilateral occipito-temporal cortices compared with conceptual recollection, suggesting that searching for novel objects heavily relies upon perceptual feature processing. Collectively, these data isolate task- from domain-sensitive PFC control processes strategically recruited in the service of episodic memory.

    View details for DOI 10.1093/cercor/bhi054

    View details for Web of Science ID 000232595700013

    View details for PubMedID 15728740

  • Transient disruption of ventrolateral prefrontal cortex during verbal encoding affects subsequent memory performance JOURNAL OF NEUROPHYSIOLOGY Kahn, I., Pascual-Leone, A., Theoret, H., Fregni, F., Clark, D., Wagner, A. D. 2005; 94 (1): 688-698

    Abstract

    Episodic memory supports conscious remembrance of everyday experience. Prior functional neuroimaging data indicate that episodic encoding during phonological task performance is correlated with activation in bilateral posterior ventrolateral prefrontal cortex (pVLPFC), although uncertainty remains regarding whether these prefrontal regions make necessary contributions to episodic memory formation. Using functional MRI data to guide application of single-pulse transcranial magnetic stimulation (spTMS), this study examined the necessity of left and right pVLPFC for episodic encoding (as expressed through subsequent memory performance). To assess the timing of critical computations, pVLPFC function was transiently disrupted at different poststimulus onset times while subjects made syllable decisions about visually presented familiar and unfamiliar words; subsequent memory for these stimuli was measured. Results revealed that left pVLPFC disruption during encoding of familiar words impaired subsequent memory, expressed as a decline in recognition confidence, with disruption being maximal at 380 ms after stimulus onset. In contrast, right pVLPFC disruption facilitated subsequent memory for familiar words, expressed as an increase in medium confidence recognition, with this facilitation being maximal at 380 ms. Finally, phonological (syllable) decision accuracy was facilitated by right pVLPFC disruption, with this effect being maximal at 340 ms, but was unaffected by left pVLPFC disruption. These findings suggest that left pVLPFC mechanisms onset between 300 and 400 ms during phonological processing of words, with these mechanisms appearing necessary for effective episodic encoding. In contrast, disruption of correlated mechanisms in right pVLPFC facilitates encoding, perhaps by inducing a functional shift in the mechanisms engaged during learning.

    View details for DOI 10.1152/jn.01335.2004

    View details for Web of Science ID 000230135500061

    View details for PubMedID 15758048

  • Hippocampal function, declarative memory, and schizophrenia: anatomic and functional neuroimaging considerations. Current neurology and neuroscience reports Preston, A. R., Shohamy, D., Tamminga, C. A., Wagner, A. D. 2005; 5 (4): 249-256

    View details for PubMedID 15987607

  • Analogical reasoning and prefrontal cortex: Evidence for separable retrieval and integration mechanisms CEREBRAL CORTEX Bunge, S. A., Wendelken, C., Badre, D., Wagner, A. D. 2005; 15 (3): 239-249

    Abstract

    The present study examined the contributions of prefrontal cortex (PFC) subregions to two component processes underlying verbal analogical reasoning: semantic retrieval and integration. Event-related functional magnetic resonance imaging data were acquired while subjects performed propositional analogy and semantic decision tasks. On each trial, subjects viewed a pair of words (pair 1), followed by an instructional cue and a second word pair (pair 2). On analogy trials, subjects evaluated whether pair 2 was semantically analogous to pair 1. On semantic trials, subjects indicated whether the pair 2 words were semantically related to each other. Thus, analogy--but not semantic--trials required integration across multiple retrieved relations. To identify regions involved in semantic retrieval, we manipulated the associative strength of pair 1 words in both tasks. Anterior left inferior PFC (aLIPC) was modulated by associative strength, consistent with a role in controlled semantic retrieval. Left frontopolar cortex was insensitive to associative strength, but was more sensitive to integration demands than was aLIPC, consistent with a role in integrating the products of semantic retrieval to evaluate whether distinct representations are analogous. Right dorsolateral PFC exhibited a profile consistent with a role in response selection rather than retrieval or integration. These findings indicate that verbal analogical reasoning depends on multiple, PFC-mediated computations.

    View details for DOI 10.1093/cercor/bhh126

    View details for Web of Science ID 000227128300001

    View details for PubMedID 15238433

  • Conceptual and perceptual novelty effects in human medial temporal cortex HIPPOCAMPUS O'Kane, G., Insler, R. Z., Wagner, A. D. 2005; 15 (3): 326-332

    Abstract

    Medial temporal lobe (MTL) structures often respond to stimulus repetition with a reduction in neural activity. Such novelty/familiarity responses reflect the mnemonic consequences of initial stimulus encounter, although the aspects of initial processing that lead to novelty/familiarity responses remain unspecified. The current functional magnetic resonance imaging (fMRI) experiment examined the sensitivity of MTL to changes in the semantic representations/processes engaged across stimulus repetitions. During initial study blocks, words were visually presented, and participants made size, shape, or composition judgments about the named referents. During repeated study blocks, the initial words were visually re-presented along with novel words, and participants made size judgments for all items. Behaviorally, responses were faster to repeated words in which the same task was performed at initial and repeated exposure (i.e., size-->size) relative to repeated words in which the tasks differed (i.e., composition-->size and shape-->size). fMRI measures revealed activation reductions in left parahippocampal cortex following same-task and different-task repetition; numerically, the effect was larger in the same-task condition. Accordingly, left parahippocampal cortex demonstrates sensitivity to perceptual novelty/familiarity, and it remains unclear whether this region also is sensitive to novelty/familiarity in the conceptual domain. In left perirhinal cortex, a novelty/familiarity effect was observed in the same-task condition but not in the different-task condition, thus revealing sensitivity to the degree of semantic overlap across exposures but insensitivity to perceptual repetition of the visual word form. Perirhinal sensitivity to semantic repetition and insensitivity to perceptual repetition suggests that human perirhinal cortex receives conceptual inputs, with perirhinal contributions to declarative memory perhaps partially stemming from its role in processing semantic aspects of experiences.

    View details for DOI 10.1002/hipo.20053

    View details for Web of Science ID 000228421600005

    View details for PubMedID 15490462

  • Prefrontal and hippocampal contributions to visual associative recognition: Interactions between cognitive control and episodic retrieval BRAIN AND COGNITION Bunge, S. A., Burrows, B., Wagner, A. D. 2004; 56 (2): 141-152

    Abstract

    The ability to recover episodic associations is thought to depend on medial-temporal lobe mnemonic mechanisms and frontal lobe cognitive control processes. The present study examined the neural circuitry underlying non-verbal associative retrieval, and considered the consequences of successful retrieval on cognitive control demands. Event-related fMRI data were acquired while subjects retrieved strongly or weakly associated pairs of novel visual patterns in a two-alternative forced choice associative recognition paradigm. Behaviorally, successful retrieval of strongly associated relative to weakly associated pairs was more likely to be accompanied by conscious recollection of the pair's prior co-occurrence. At the neural level, right ventrolateral prefrontal cortex (VLPFC) and hippocampus were more active during successful retrieval of Strong than of Weak associations, consistent with a role in visual associative recollection. By contrast, Weak trials elicited greater activation in right anterior cingulate cortex (ACC), which may detect conflict between the similarly familiar target and foil stimuli in the absence of recollection. Consistent with this interpretation, stronger ACC activity was associated with weaker hippocampal and stronger right dorsolateral PFC (DLPFC) responses. Thus, recollection of relevant visual associations (hippocampus and VLPFC) results in lower levels of mnemonic conflict (ACC) and decreased familiarity-based monitoring demands (DLPFC). These findings highlight the interplay between cognitive control and episodic retrieval.

    View details for DOI 10.1016/j.bandc.2003.08.001

    View details for Web of Science ID 000225113600002

    View details for PubMedID 15518931

  • What can neuroimaging tell us about the mind? Insights from prefrontal cortex CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE Poldrack, R. A., Wagner, A. D. 2004; 13 (5): 177-181
  • Functional-neuroanatomic correlates of recollection: Implications for models of recognition memory JOURNAL OF NEUROSCIENCE Kahn, I., Davachi, L., Wagner, A. D. 2004; 24 (17): 4172-4180

    Abstract

    Recognition decisions can be based on familiarity, the sense that an item was encountered previously (item memory), and on recollection, the conscious recovery of contextual information surrounding a previous encounter with the item (e.g., source memory). Recognition with recollection is thought to depend on multiple mechanisms, including prefrontal "control" processes that guide retrieval and recapitulation mechanisms that reactivate posterior neocortical representations that were present at encoding. However, uncertainty remains regarding the precise nature of prefrontal contributions to recollection and the selectivity of recapitulation to veridical recollection. The present event-related functional magnetic resonance imaging study sought to examine whether regions showing "old-new" effects support processes sensitive to recollection success or recollection attempt and whether recapitulation of neocortical representations emerge during veridical recollection as well as during false recognition (i.e., false alarms) or whether false recognition resembles familiarity-based responding. Results revealed that multiple left prefrontal cortical regions were engaged during attempts to recollect previous contextual (source) details, regardless of the nature of the to-be-recollected details and of source recollection outcome (successful vs unsuccessful). Recapitulation effects were observed in regions sensitive to the encoding task, suggesting that veridical recollection entails the reactivation of processes or representations present during encoding. Importantly, in contrast to leading models of recognition memory, false alarms also appeared to be based partially on recollection, as revealed through false recapitulation effects. Implications for neural and cognitive models of recognition are considered.

    View details for DOI 10.1523/JNEUROSCI.0624-04.2004

    View details for Web of Science ID 000221195100008

    View details for PubMedID 15115812

  • Item- and task-level processes in the left inferior prefrontal cortex: positive and negative correlates of encoding NEUROIMAGE Reynolds, J. R., Donaldson, D. I., Wagner, A. D., Braver, T. S. 2004; 21 (4): 1472-1483

    Abstract

    Activity in the left inferior prefrontal cortex (LIPC) is often thought to reflect processes that support episodic encoding. Functional magnetic resonance imaging (fMRI) was used to test whether processes subserved by LIPC could be negatively related to subsequent memory performance. Specifically, the current experiment explicitly tested the hypothesis that LIPC processing would positively impact encoding when primarily focused towards specific target items (item-level processing), whereas it would negatively impact encoding when primarily focused on the retrieval and instantiation of current task instructions (task-level processing). Two methods were used to identify regions that were sensitive to the two types of processes: a block-level manipulation of encoding task that influenced subsequent memory, and a back-sort procedure. LIPC was sensitive to item- and task-level processing, but not in a way that always facilitates encoding. LIPC was more active for subsequently remembered words than subsequently forgotten words, but it was also more active in a task that emphasized task-level processing relative to a task that emphasized item-level processing, although this former condition led to poorer subsequent memory performance. This pattern indicates that processes subserved by LIPC are not always positively correlated with episodic encoding. Rather, LIPC processes can support both the controlled semantic processing of items and the controlled retrieval of relevant semantic task context. When devoted to the latter, the diversion of LIPC processes to the task level can have a negative consequence for item-level analysis and encoding.

    View details for DOI 10.1016/j.neuroimage.2003.10.033

    View details for Web of Science ID 000220723900026

    View details for PubMedID 15050572

  • Neural circuits subserving the retrieval and maintenance of abstract rules JOURNAL OF NEUROPHYSIOLOGY Bunge, S. A., Kahn, I., Wallis, J. D., Miller, E. K., Wagner, A. D. 2003; 90 (5): 3419-3428

    Abstract

    Behavior is often governed by abstract rules or instructions for behavior that can be abstracted from one context and applied to another. Prefrontal cortex (PFC) is thought to be important for representing rules, although the contributions of ventrolateral (VLPFC) and dorsolateral (DLPFC) regions remain under-specified. In the present study, event-related fMRI was used to examine abstract rule representation in humans. Prior to scanning, subjects learned to associate unfamiliar shapes and nonwords with particular rules. During each fMRI trial, presentation of one of these cues was followed by a delay and then by sample and probe stimuli. Match and non-match rules required subjects to indicate whether or not the sample and probe matched; go rules required subjects to make a response that was not contingent on the sample/probe relation. Left VLPFC, parietal cortex, and pre-SMA exhibited sensitivity to rule type during the cue and delay periods. Delay-period activation in these regions, but not DLPFC, was greater when subjects had to maintain response contingencies (match, non-match) relative to when the cue signaled a specific response (go). In contrast, left middle temporal cortex exhibited rule sensitivity during the cue but not delay period. These results support the hypothesis that VLPFC interacts with temporal cortex to retrieve semantic information associated with a cue and with parietal cortex to retrieve and maintain relevant response contingencies across delays. Future investigations of cross-regional interactions will enable full assessment of this account. Collectively, these results demonstrate that multiple, neurally separable processes are recruited during abstract rule representation.

    View details for DOI 10.1152/jn.00910.2002

    View details for Web of Science ID 000186547600052

    View details for PubMedID 12867532

  • Neural mechanisms of visual object priming: evidence for perceptual and semantic distinctions in fusiform cortex NEUROIMAGE Simons, J. S., Koutstaal, W., Prince, S., Wagner, A. D., Schacter, D. L. 2003; 19 (3): 613-626

    Abstract

    Previous functional imaging studies have shown that facilitated processing of a visual object on repeated, relative to initial, presentation (i.e., repetition priming) is associated with reductions in neural activity in multiple regions, including fusiform/lateral occipital cortex. Moreover, activity reductions have been found, at diminished levels, when a different exemplar of an object is presented on repetition. In one previous study, the magnitude of diminished priming across exemplars was greater in the right relative to the left fusiform, suggesting greater exemplar specificity in the right. Another previous study, however, observed fusiform lateralization modulated by object viewpoint, but not object exemplar. The present fMRI study sought to determine whether the result of differential fusiform responses for perceptually different exemplars could be replicated. Furthermore, the role of the left fusiform cortex in object recognition was investigated via the inclusion of a lexical/semantic manipulation. Right fusiform cortex showed a significantly greater effect of exemplar change than left fusiform, replicating the previous result of exemplar-specific fusiform lateralization. Right fusiform and lateral occipital cortex were not differentially engaged by the lexical/semantic manipulation, suggesting that their role in visual object recognition is predominantly in the visual discrimination of specific objects. Activation in left fusiform cortex, but not left lateral occipital cortex, was modulated by both exemplar change and lexical/semantic manipulation, with further analysis suggesting a posterior-to-anterior progression between regions involved in processing visuoperceptual and lexical/semantic information about objects. The results are consistent with the view that the right fusiform plays a greater role in processing specific visual form information about objects, whereas the left fusiform is also involved in lexical/semantic processing.

    View details for DOI 10.1016/S1053-8119(03)00096-X

    View details for Web of Science ID 000184485400012

    View details for PubMedID 12880792

  • Assembling and encoding word representations: fMRI subsequent memory effects implicate a role for phonological control NEUROPSYCHOLOGIA Clark, D., Wagner, A. D. 2003; 41 (3): 304-317

    Abstract

    Novel word learning is central to the flexibility inherent in the human language capacity. Word learning may partially depend on long-term memory formation during the assembly of phonological representations from orthographic inputs. In the present study, event-related functional magnetic resonance imaging (fMRI) examined the contributions of phonological control-a component of the verbal working memory system-to phonological assembly and word learning. Subjects were scanned while making syllable decisions about visually presented familiar (English) and novel (pseudo-English and Foreign) words, a task that required retrieval and analysis of existing phonological codes or the assembly and analysis of novel representations. Results revealed that left inferior prefrontal cortex (LIPC) and bilateral parietal cortices were differentially engaged during the processing of novel words, suggesting that this circuit is recruited during phonological assembly. A subsequent memory analysis that examined the relation between fMRI signal and the subject's ability to later remember the words (a measure of effective memory formation) revealed that the magnitude of activation in LIPC, bilateral superior parietal, and left inferior parietal cortices was positively correlated with later memory. Moreover, although the magnitude of the subsequent memory effect in parietal cortex was not significantly affected by word type, this effect was greater in posterior LIPC for novel (pseudo-English) than for familiar (English) words. In the course of subserving the assembly of novel word representations, the phonological (articulatory) control component of the phonological system appears to play a central role in the encoding of novel words into long-term memory.

    View details for Web of Science ID 000179889700008

    View details for PubMedID 12457756

  • Memory orientation and success: separable neurocognitive components underlying episodic recognition NEUROPSYCHOLOGIA Dobbins, I. G., Rice, H. J., Wagner, A. D., Schacter, D. L. 2003; 41 (3): 318-333

    Abstract

    Episodic recognition can be based on recollection of contextual details, on a sense of recent encounter, or some combination of the two. According to several cognitive models, selectively attending to these distinct aspects of memory may require different retrieval orientations and result in different neural responses depending upon whether or not retrieval is successful. Using event-related fMRI, we examined retrieval orientation by having subjects discriminate between two test words in one of two manners. During source recollection, they selected the member of the pair previously associated with a particular encoding task. In contrast, recency judgment required selection of the most recently encountered item of the pair, regardless of how it had been encoded. Furthermore, successful and unsuccessful trials within each retrieval task were contrasted to determine whether retrieval success effects occurred in overlapping or dissimilar neural populations compared to those associated with each retrieval orientation. The results revealed distinct lateral prefrontal and parietal activations that distinguished attempted source recollection from judgments of relative recency; these orientation effects were largely independent of retrieval success. In contrast, medial temporal lobe structures (hippocampus and parahippocampal gyrus) were differentially more active during successful recollection of encoding context, showing similar reduced responses during failed source recollection and judgments of recency. These results indicate that different memory orientations recruit distinct prefrontal and parietal networks and that the recovery of episodic context is associated with the hippocampus and surrounding medial temporal cortices.

    View details for Web of Science ID 000179889700009

    View details for PubMedID 12457757

  • Semantic retrieval, mnemonic control, and prefrontal cortex. Behavioral and cognitive neuroscience reviews Badre, D., Wagner, A. D. 2002; 1 (3): 206-218

    Abstract

    Accessing stored knowledge is a fundamental function of the cognitive and neural architectures of memory. Here, the authors review evidence from cognitive-behavioral paradigms, neuropsychological studies of patients with focal neural insult, and functional brain imaging concerning the mechanisms underlying retrieval of semantic knowledge and their association with prefrontal cortex. First, the authors examine behavioral and neuropsychological evidence distinguishing between controlled and automatic semantic retrieval. Then the authors review the subregions of prefrontal cortex that functional neuroimaging has associated with semantic retrieval across a range of memory demanding tasks. Finally, two hypotheses concerning the nature of processing in these brain regions--the controlled semantic retrieval and selection hypotheses--are critically examined, and a possible synthesis is proposed.

    View details for PubMedID 17715593

  • Hippocampal contributions to episodic encoding: Insights from relational and item-based learning JOURNAL OF NEUROPHYSIOLOGY Davachi, L., Wagner, A. D. 2002; 88 (2): 982-990

    Abstract

    The integrity of the hippocampus and surrounding medial-temporal cortices is critical for episodic memory, with the hippocampus being posited to support relational or configural associative learning. The present event-related functional magnetic resonance imaging (fMRI) study investigated the role of specific medial-temporal lobe structures in learning during relational and item-based processing, as well as the extent to which these structures are engaged during item-based maintenance of stimuli in working memory. fMRI indexed involvement of the hippocampus and underlying cortical regions during performance of two verbal encoding conditions, one that required item-based maintenance of word triplets in working memory and the other that entailed the formation of inter-item associations across the words in each triplet. Sixteen subjects were scanned using a rapid event-related fMRI design while they encountered the item-based and relational processing trials. To examine the correlation between fMRI signal in medial-temporal structures during learning and the subject's subsequent ability to remember the stimuli (a measure of effective memory formation), subjects were administered a yes-no recognition memory test following completion of the encoding scans. Results revealed that the hippocampus proper was engaged during both relational and item-based processing, with relational processing resulting in a greater hippocampal response. By contrast, entorhinal and parahippocampal gyri were differentially engaged during item-based processing, providing strong evidence for a functional neuroanatomic distinction between hippocampal and parahippocampal structures. Analysis of the neural correlates of subsequent memory revealed that activation in the bilateral hippocampus was reliably correlated with behavioral measures of effective memory formation only for those stimuli that were encoded in a relational manner. Taken together, these data provide evidence that the hippocampus, while engaged during item-based working memory maintenance, differentially subserves the relational binding of items into an integrated memory trace so that the experience can be later remembered.

    View details for DOI 10.1152/jn00046.2002

    View details for Web of Science ID 000177276100039

    View details for PubMedID 12163547

  • Synchronicity: when you're gone I'm lost without a trace? NATURE NEUROSCIENCE Wagner, A. D. 2001; 4 (12): 1159-1160

    View details for Web of Science ID 000172525000005

    View details for PubMedID 11723457

  • Prefrontal contributions to executive control: fMRI evidence for functional distinctions within lateral prefrontal cortex NEUROIMAGE Wagner, A. D., Maril, A., Bjork, R. A., Schacter, D. L. 2001; 14 (6): 1337-1347

    Abstract

    The prefrontal cortex (PFC) plays a fundamental role in internally guided behavior. Although it is generally accepted that PFC subserves working memory and executive control operations, it remains unclear whether the subregions within lateral PFC support distinct executive control processes. An event-related fMRI study was implemented to test the hypothesis that ventrolateral and dorsolateral PFC are functionally distinct, as well as to assess whether functional specialization exists within ventrolateral PFC. Participants performed two executive control tasks that differed in the types of control processes required. During rote rehearsal, participants covertly rehearsed three words in the order presented, thus requiring phonological access and maintenance. During elaborative rehearsal, participants made semantic comparisons between three words held in working memory, reordering them from least to most desirable. Thus, in addition to maintenance, elaborative rehearsal required goal-relevant coding of items in working memory ("monitoring") and selection from among the items to implement their reordering. Results revealed that left posterior ventrolateral PFC was active during performance of both tasks, whereas right dorsolateral PFC was differentially engaged during elaborative rehearsal. The temporal characteristics of the hemodynamic responses further suggested that dorsolateral activation lagged ventrolateral activation. Finally, differential activation patterns were observed within left ventrolateral PFC, distinguishing between posterior and anterior regions. These data suggest that anatomically separable subregions within lateral PFC may be functionally distinct and are consistent with models that posit a hierarchical relationship between dorsolateral and ventrolateral regions such that the former monitors and selects goal-relevant representations being maintained by the latter.

    View details for DOI 10.1006/nimg.2001.0936

    View details for Web of Science ID 000172524500010

    View details for PubMedID 11707089

  • Cognitive neuroscience: Forgetting of things past CURRENT BIOLOGY Wagner, A. D., Davachi, L. 2001; 11 (23): R964-R967

    Abstract

    Recent functional imaging and electrophysiological results indicate that failure to remember experiences can result from a decreased recruitment of encoding processes that build effective memories and an increased recruitment of alternative mechanisms that may impair effective learning.

    View details for Web of Science ID 000172475700009

    View details for PubMedID 11728323

  • When keeping in mind supports later bringing to mind: Neural markers of phonological rehearsal predict subsequent remembering JOURNAL OF COGNITIVE NEUROSCIENCE Davachi, L., Maril, A., Wagner, A. D. 2001; 13 (8): 1059-1070

    Abstract

    The ability to bring to mind a past experience depends on the cognitive and neural processes that are engaged during the experience and that support memory formation. A central and much debated question is whether the processes that underlie rote verbal rehearsal-that is, working memory mechanisms that keep information in mind-impact memory formation and subsequent remembering. The present study used event-related functional magnetic resonance imaging (fMRI) to explore the relation between working memory maintenance operations and long-term memory. Specifically, we investigated whether the magnitude of activation in neural regions supporting the on-line maintenance of verbal codes is predictive of subsequent memory for words that were rote-rehearsed during learning. Furthermore, during rote rehearsal, the extent of neural activation in regions associated with semantic retrieval was assessed to determine the role that incidental semantic elaboration may play in subsequent memory for rote-rehearsed items. Results revealed that (a) the magnitude of activation in neural regions previously associated with phonological rehearsal (left prefrontal, bilateral parietal, supplementary motor, and cerebellar regions) was correlated with subsequent memory, and (b) while rote rehearsal did not--on average--elicit activation in an anterior left prefrontal region associated with semantic retrieval, activation in this region was greater for trials that were subsequently better remembered. Contrary to the prevalent view that rote rehearsal does not impact learning, these data suggest that phonological maintenance mechanisms, in addition to semantic elaboration, support the encoding of an experience such that it can be later remembered.

    View details for Web of Science ID 000172629900003

    View details for PubMedID 11784444

  • Can medial temporal lobe regions distinguish true from false? An event-related functional MRI study of veridical and illusory recognition memory PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Cabeza, R., Rao, S. M., Wagner, A. D., Mayer, A. R., Schacter, D. L. 2001; 98 (8): 4805-4810

    Abstract

    To investigate the types of memory traces recovered by the medial temporal lobe (MTL), neural activity during veridical and illusory recognition was measured with the use of functional MRI (fMRI). Twelve healthy young adults watched a videotape segment in which two speakers alternatively presented lists of associated words, and then the subjects performed a recognition test including words presented in the study lists (True items), new words closely related to studied words (False items), and new unrelated words (New items). The main finding was a dissociation between two MTL regions: whereas the hippocampus was similarly activated for True and False items, suggesting the recovery of semantic information, the parahippocampal gyrus was more activated for True than for False items, suggesting the recovery of perceptual information. The study also yielded a dissociation between two prefrontal cortex (PFC) regions: whereas bilateral dorsolateral PFC was more activated for True and False items than for New items, possibly reflecting monitoring of retrieved information, left ventrolateral PFC was more activated for New than for True and False items, possibly reflecting semantic processing. Precuneus and lateral parietal regions were more activated for True and False than for New items. Orbitofrontal cortex and cerebellar regions were more activated for False than for True items. In conclusion, the results suggest that activity in anterior MTL regions does not distinguish True from False, whereas activity in posterior MTL regions does.

    View details for Web of Science ID 000168059700096

    View details for PubMedID 11287664

  • Prefrontal regions supporting spontaneous and directed application of verbal learning strategies - Evidence from PET BRAIN Savage, C. R., Deckersbach, T., Heckers, S., Wagner, A. D., Schacter, D. L., Alpert, N. M., Fischman, A. J., Rauch, S. L. 2001; 124: 219-231

    Abstract

    The prefrontal cortex has been implicated in strategic memory processes, including the ability to use semantic organizational strategies to facilitate episodic learning. An important feature of these strategies is the way they are applied in novel or ambiguous situations-failure to initiate effective strategies spontaneously in unstructured settings is a central cognitive deficit in patients with frontal lobe disorders. The current study examined strategic memory with PET and a verbal encoding paradigm that manipulated semantic organization in three encoding conditions: spontaneous, directed and unrelated. During the spontaneous condition, subjects heard 24 words that were related in four categories but presented in mixed order, and they were not informed of this structure beforehand. Any semantic reorganization was, therefore, initiated spontaneously by the subject. In the directed condition, subjects were given a different list of 24 related words and explicitly instructed to notice relationships and mentally group related words together to improve memory. The unrelated list consisted of 24 unrelated words. Behavioural measures included semantic clustering, which assessed active regrouping of words into semantic categories during free recall. In graded PET contrasts (directed > spontaneous > unrelated), two distinct activations were found in left inferior prefrontal cortex (inferior frontal gyrus) and left dorsolateral prefrontal cortex (middle frontal gyrus), corresponding to levels of semantic clustering observed in the behavioural data. Additional covariate analyses in the first spontaneous condition indicated that blood flow in orbitofrontal cortex (OFC) was strongly correlated with semantic clustering scores during immediate free recall. Thus, blood flow in OFC during encoding predicted which subjects would spontaneously initiate effective strategies during free recall. Our findings indicate that OFC performs an important, and previously unappreciated, role in strategic memory by supporting the early mobilization of effective behavioural strategies in novel or ambiguous situations. Once initiated, lateral regions of left prefrontal cortex control verbal semantic organization.

    View details for Web of Science ID 000166619900019

    View details for PubMedID 11133799

  • Perceptual specificity in visual object priming: functional magnetic resonance imaging evidence for a laterality difference in fusiform cortex NEUROPSYCHOLOGIA Koutstaal, W., Wagner, A. D., Rotte, M., Maril, A., Buckner, R. L., Schacter, D. L. 2001; 39 (2): 184-199

    Abstract

    Seeing an object on one occasion may facilitate or prime processing of the same object if it is later again encountered. Such priming may also be found -- but at a reduced level -- for different but perceptually similar objects that are alternative exemplars or 'tokens' of the initially presented object. We explored the neural correlates of this perceptual specificity using event-related functional magnetic resonance imaging (fMRI) procedures, contrasting neural activity when participants made object classification decisions (size judgments) regarding previously presented objects (repeated same), alternative exemplars of previously presented objects (repeated different), or entirely new objects (novel). Many frontal regions (including bilateral frontal operculum, bilateral posterior inferior frontal/precentral, left anterior inferior frontal, and superior frontal cortices) and multiple late visual and posterior regions (including middle occipital, fusiform, fusiform-parahippocampal, precuneus, and posterior cingulate, all bilaterally), demonstrated reduced neural activity for repeated compared to novel objects. Greater repetition-induced reductions were observed for same than for different exemplars in several of these regions (bilateral posterior inferior frontal, right precuneus, bilateral middle occipital, bilateral fusiform, bilateral parahippocampal and bilateral superior parietal). Additionally, right fusiform (occipitotemporal) cortex showed significantly less priming for different versus same exemplars than did left fusiform. These findings converge with behavioral evidence from divided visual field studies and with neuropsychological evidence underscoring the key role of right occipitotemporal cortex in processing specific visual form information; possible differences in the representational-functional role of left fusiform are discussed.

    View details for Web of Science ID 000166054800008

    View details for PubMedID 11163375

  • Task-specific repetition priming in left inferior prefrontal cortex CEREBRAL CORTEX Wagner, A. D., Koutstaal, W., Maril, A., Schacter, D. L., Buckner, R. L. 2000; 10 (12): 1176-1184

    Abstract

    Previous neuroimaging studies have shown that activation in left inferior prefrontal cortices (LIPC) is reduced during repeated (primed) relative to initial (unprimed) stimulus processing. These reductions in anterior (approximately BA 45/47) and posterior (approximately BA 44/6) LIPC activation have been interpreted as reflecting implicit memory for initial semantic or phonological processing. However, prior studies do not unambiguously indicate that LIPC priming effects are specific to the recapitulation of higher-level (semantic and/or phonological), rather than lower-level (perceptual), processes. Moreover, no prior study has shown that the patterns of priming in anterior and posterior LIPC regions are dissociable. To address these issues, the present fMRI study examined the nature of priming in LIPC by examining the task-specificity of these effects. Participants initially processed words in either a semantic or a nonsemantic manner. Subsequently, participants were scanned while they made semantic decisions about words that had been previously processed in a semantic manner (within-task repetition), words that had been previously processed in a nonsemantic manner (across-task repetition), and words that had not been previously processed (novel words). Behaviorally, task-specific priming was observed: reaction times to make the semantic decision declined following prior semantic processing but not following prior nonsemantic processing of a word. Priming in anterior LIPC paralleled these results with signal reductions being observed following within-task, but not following across-task, repetition. Importantly, neural priming in posterior LIPC demonstrated a different pattern: priming was observed following both within-task and across-task repetition, with the magnitude of priming tending to be greater in the within-task condition. Direct comparison between anterior and posterior LIPC regions revealed a significant interaction. These findings indicate that anterior and posterior LIPC demonstrate distinct patterns of priming, with priming in the anterior region being task-specific, suggesting that this facilitation derives from repeated semantic processing of a stimulus.

    View details for Web of Science ID 000165526700003

    View details for PubMedID 11073867

  • Early detection of Alzheimer's disease: An fMRI marker for people at risk? NATURE NEUROSCIENCE Wagner, A. D. 2000; 3 (10): 973-974

    View details for Web of Science ID 000167177500012

    View details for PubMedID 11017166

  • Interactions between forms of memory: When priming hinders new episodic learning JOURNAL OF COGNITIVE NEUROSCIENCE Wagner, A. D., Maril, A., Schacter, D. L. 2000; 12: 52-60

    Abstract

    Human memory consists of multiple forms, including priming and explicit memory. Although considerable evidence indicates that priming and explicit memory are functionally and neuroanatomically distinct, little is know about when and how these different forms of memory interact. Here, behavioral and functional magnetic resonance imaging (fMRI) methods were used to examine a novel and counterintuitive hypothesis: Priming during episodic encoding may be negatively associated with subsequent explicit memory. Using an experimental design that exploited known properties of spacing or lag effects, the magnitudes of behavioral and neural priming during a second study episode were varied and the relation between these magnitudes of priming during re-encoding and performance on a subsequent explicit memory test was examined. Results revealed that greater behavioral priming (reduced reaction times) and neural priming (reduced left inferior prefrontal brain activation) during re-encoding were associated with lower levels of subsequent explicit memory. Moreover, those subjects who demonstrated greater behavioral and neural priming effects during re-encoding following a long lag tended to demonstrate the least benefit in subsequent explicit memory due to this second study episode. These findings suggest that priming for past experiences can hinder new episodic encoding.

    View details for Web of Science ID 000166194100006

    View details for PubMedID 11506647

  • Convergent cortical representation of semantic processing in bilinguals BRAIN AND LANGUAGE Illes, J., Francis, W. S., Desmond, J. E., Gabrieli, J. D., Glover, G. H., Poldrack, R., Lee, C. J., Wagner, A. D. 1999; 70 (3): 347-363

    Abstract

    This study examined whether semantic processes in two languages (English and Spanish) are mediated by a common neural system in fluent bilinguals who acquired their second language years after acquiring their first language. Functional magnetic resonance imaging was performed while bilingual participants made semantic and nonsemantic decisions about words in Spanish and English. There was greater activation for semantic relative to nonsemantic decisions in left and right frontal regions, with greater left frontal activation. The locations of activations were similar for both languages, and no differences were found when semantic decisions for English and Spanish words were compared directly. These results demonstrate a shared frontal lobe system for semantic analysis of the languages and are consistent with cognitive research on bilingualism indicating that the two languages of a bilingual person access a common semantic system.

    View details for Web of Science ID 000084152700003

    View details for PubMedID 10600225

  • Perspectives: Neuroscience - Remembrance of things past SCIENCE Schacter, D. L., Wagner, A. D. 1999; 285 (5433): 1503-1504

    View details for Web of Science ID 000082359500038

    View details for PubMedID 10498535

  • When encoding yields remembering: insights from event-related neuroimaging PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Wagner, A. D., Koutstaal, W., Schacter, D. L. 1999; 354 (1387): 1307-1324

    Abstract

    To understand human memory, it is important to determine why some experiences are remembered whereas others are forgotten. Until recently, insights into the neural bases of human memory encoding, the processes by which information is transformed into an enduring memory trace, have primarily been derived from neuropsychological studies of humans with select brain lesions. The advent of functional neuroimaging methods, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), has provided a new opportunity to gain additional understanding of how the brain supports memory formation. Importantly, the recent development of event-related fMRI methods now allows for examination of trial-by-trial differences in neural activity during encoding and of the consequences of these differences for later remembering. In this review, we consider the contributions of PET and fMRI studies to the understanding of memory encoding, placing a particular emphasis on recent event-related fMRI studies of the Dm effect: that is, differences in neural activity during encoding that are related to differences in subsequent memory. We then turn our attention to the rich literature on the Dm effect that has emerged from studies using event-related potentials (ERPs). It is hoped that the integration of findings from ERP studies, which offer higher temporal resolution, with those from event-related fMRI studies, which offer higher spatial resolution, will shed new light on when and why encoding yields subsequent remembering.

    View details for Web of Science ID 000081832800015

    View details for PubMedID 10466153

  • Functional specialization for semantic and phonological processing in the left inferior prefrontal cortex NEUROIMAGE Poldrack, R. A., Wagner, A. D., Prull, M. W., Desmond, J. E., Glover, G. H., Gabrieli, J. D. 1999; 10 (1): 15-35

    Abstract

    Neuroimaging and neuropsychological studies have implicated left inferior prefrontal cortex (LIPC) in both semantic and phonological processing. In this study, functional magnetic resonance imaging was used to examine whether separate LIPC regions participate in each of these types of processing. Performance of a semantic decision task resulted in extensive LIPC activation compared to a perceptual control task. Phonological processing of words and pseudowords in a syllable-counting task resulted in activation of the dorsal aspect of the left inferior frontal gyrus near the inferior frontal sulcus (BA 44/45) compared to a perceptual control task, with greater activation for nonwords compared to words. In a direct comparison of semantic and phonological tasks, semantic processing preferentially activated the ventral aspect of the left inferior frontal gyrus (BA 47/45). A review of the literature demonstrated a similar distinction between left prefrontal regions involved in semantic processing and phonological/lexical processing. The results suggest that a distinct region in the left inferior frontal cortex is involved in semantic processing, whereas other regions may subserve phonological processes engaged during both semantic and phonological tasks.

    View details for Web of Science ID 000081454800003

    View details for PubMedID 10385578

  • Medial temporal lobe activations in fMRI and PET studies of episodic encoding and retrieval HIPPOCAMPUS Schacter, D. L., Wagner, A. D. 1999; 9 (1): 7-24

    Abstract

    Early neuroimaging studies often failed to obtain evidence of medial temporal lobe (MTL) activation during episodic encoding or retrieval, but a growing number of studies using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) have provided such evidence. We review data from fMRI studies that converge on the conclusion that posterior MTL is associated with episodic encoding; too few fMRI studies of retrieval have reported MTL activations to allow firm conclusions about their exact locations. We then turn to a recent meta-analysis of PET studies (Lepage et al., Hippocampus 1998;8:313-322) that appears to contradict the fMRI encoding data. Based on their analysis of the rostrocaudal distribution of activations reported during episodic encoding or retrieval, Lepage et al. (1998) concluded that anterior MTL is strongly associated with episodic encoding, whereas posterior MTL is strongly associated with episodic retrieval. After considering the evidence reviewed by Lepage et al. (1998) along with additional studies, we conclude that PET studies of encoding reveal both anterior and posterior MTL activations. These observations indicate that the contradiction between fMRI and PET studies of encoding was more apparent than real. However, PET studies have reported anterior MTL encoding activations more frequently than have fMRI studies. We consider possible sources of these differences.

    View details for Web of Science ID 000079002000002

    View details for PubMedID 10088896

  • Material-specific lateralization of prefrontal activation during episodic encoding and retrieval NEUROREPORT Wagner, A. D., Poldrack, R. A., Eldridge, L. L., Desmond, J. E., Glover, G. H., Gabrieli, J. D. 1998; 9 (16): 3711-3717

    Abstract

    Although numerous neuroimaging studies have examined the functional neuroanatomy supporting episodic memory for verbal material, there have been few investigations of non-verbal episodic encoding and retrieval. We used fMRI to directly compare prefrontal activation elicited by verbal and non-verbal material during encoding and during retrieval. Regardless of the mnemonic operation (encoding/retrieval), inferior prefrontal activation lateralized based on material type. Verbal encoding and retrieval resulted in greater left inferior prefrontal activation, whereas non-verbal encoding and retrieval resulted in greater right inferior prefrontal activation. The similarity between inferior prefrontal activity during encoding and during retrieval indicates that these mnemonic operations depend on shared processes mediated by inferior prefrontal regions.

    View details for Web of Science ID 000077493400030

    View details for PubMedID 9858384

  • Prefrontal cortex and recognition memory - Functional-MRI evidence for context-dependent retrieval processes BRAIN Wagner, A. D., Desmond, J. E., Glover, G. H., Gabrieli, J. D. 1998; 121: 1985-2002

    Abstract

    Functional neuroimaging studies of episodic recognition memory consistently demonstrate retrieval-associated activation in right prefrontal regions, including the right anterior and right dorsolateral prefrontal cortices. In theory, these activations could reflect processes associated with retrieval success, retrieval effort or retrieval attempt; each of these hypotheses has some support from previous studies. In Experiment 1, we examined these functional interpretations using functional MRI to measure prefrontal activation across multiple levels of recognition performance. Results revealed similar patterns of right prefrontal activation across varying levels of retrieval success and retrieval effort, suggesting that these activations reflect retrieval attempt. Retrieval attempt may include initiation of retrieval search or evaluation of the products of retrieval, such as scrutiny of specific attributes of the test item in an effort to determine whether it was encountered previously. In Experiment 2, we examined whether engagement of retrieval attempt is context-dependent by varying the context in which retrieval was performed; this was done by changing test instructions. Importantly, study and test stimuli were held constant, with only the test instructions varying across conditions. Results revealed that the pattern of right prefrontal activation varied across retrieval contexts. Collectively, these experiments suggest that right prefrontal regions mediate processes associated with retrieval attempt, with the probability of engaging these regions depending upon the retrieval context. Conflicting results across previous studies may be reconciled if the influence of retrieval context on the adopted retrieval strategy is considered. Finally, these results suggest that right prefrontal regions activated during recognition are not critical for successful performance as similar magnitudes of activation were present across multiple levels of performance. These findings reconcile imaging results with the selective effects of prefrontal lesions on retrieval-intensive episodic memory tests.

    View details for Web of Science ID 000076550700013

    View details for PubMedID 9798751

  • Neuropsychological dissociation between recognition familiarity and perceptual priming in visual long-term memory CORTEX Wagner, A. D., Stebbins, G. T., Masciari, F., Fleischman, D. A., Gabrieli, J. D. 1998; 34 (4): 493-511

    Abstract

    The present study examined whether the same brain region mediates visual-perceptual repetition priming and a familiarity component of visual recognition memory. In two experiments, familiarity-based recognition was measured in an individual (M.S.) with impaired visual repetition priming due to a lesion of right occipital cortex. In both experiments, M.S. demonstrated intact recognition familiarity despite his visual nondeclarative memory impairment. These results converge with other behavioral results to indicate that recognition familiarity does not depend on the same memory system that mediates perceptual priming.

    View details for Web of Science ID 000076443900002

    View details for PubMedID 9800086

  • Functional-anatomic study of episodic retrieval using fMRI I. Retrieval effort versus retrieval success NEUROIMAGE Buckner, R. L., Koutstaal, W., Schacter, D. L., Wagner, A. D., Rosen, B. R. 1998; 7 (3): 151-162

    Abstract

    A number of recent functional imaging studies have identified brain areas activated during tasks involving episodic memory retrieval. The identification of such areas provides a foundation for targeted hypotheses regarding the more specific contributions that these areas make to episodic retrieval. As a beginning effort toward such an endeavor, whole-brain functional magnetic resonance imaging (fMRI) was used to examine 14 subjects during episodic word recognition in a block-designed fMRI experiment. Study conditions were manipulated by presenting either shallow or deep encoding tasks. This manipulation yielded two recognition conditions that differed with regard to retrieval effort and retrieval success: shallow encoding yielded low levels of recognition success with high levels of retrieval effort, and deep encoding yielded high levels of recognition success with low levels of effort. Many brain areas were activated in common by these two recognition conditions compared to a low-level fixation condition, including left and right prefrontal regions often detected during PET episodic retrieval paradigms (e.g., R. L. Buckner et al., 1996, J. Neurosci. 16, 6219-6235) thereby generalizing these findings to fMRI. Characterization of the activated regions in relation to the separate recognition conditions showed (1) bilateral anterior insular regions and a left dorsal prefrontal region were more active after shallow encoding, when retrieval demanded greatest effort, and (2) right anterior prefrontal cortex, which has been implicated in episodic retrieval, was most active during successful retrieval after deep encoding. We discuss these findings in relation to component processes involved in episodic retrieval and in the context of a companion study using event-related fMRI.

    View details for Web of Science ID 000073589600001

    View details for PubMedID 9597657

  • On the relationship between recognition familiarity and perceptual fluency: Evidence for distinct mnemonic processes ACTA PSYCHOLOGICA Wagner, A. D., Gabrieli, J. D. 1998; 98 (2-3): 211-230

    Abstract

    Fluent reprocessing of perceptual aspects of recently experienced stimuli is thought to support repetition priming effects on implicit perceptual memory tests. Although behavioral and neuropsychological dissociations demonstrate that separable mnemonic processes and neural substrates mediate implicit and explicit test performance, dual-process theories of memory posit that explicit recognition memory judgments may be based on familiarity derived from the same perceptual fluency that yields perceptual priming. Here we consider the relationship between familiarity-based recognition memory and implicit perceptual memory. A select review of the literature demonstrates that the fluency supporting implicit perceptual memory is functionally and anatomically distinct from that supporting recognition memory. In contrast to perceptual fluency, recognition familiarity is more sensitive to conceptual than to perceptual processing, and does not depend on modality-specific sensory cortices. Alternative possible relationships between familiarity in explicit memory and fluency in implicit memory are discussed.

    View details for Web of Science ID 000073902500006

    View details for PubMedID 9621831

  • Lobular patterns of cerebellar activation in verbal working-memory and finger-tapping tasks as revealed by functional MRI JOURNAL OF NEUROSCIENCE Desmond, J. E., Gabrieli, J. D., Wagner, A. D., GINIER, B. L., Glover, G. H. 1997; 17 (24): 9675-9685

    Abstract

    The lobular distributions of functional activation of the cerebellum during verbal working-memory and finger movement tasks were investigated using functional magnetic resonance imaging (fMRI). Relative to a rest control, finger tapping of the right hand produced ipsilateral-increased activation in HIV/HV [Roman numeral designations based on Larsell's () nomenclature] and HVI and weaker activation in HVIII that was stronger on the ipsilateral side. For a working-memory task, subjects were asked to remember six (high load) or one (low load) visually presented letters across a brief delay. To assess the motoric aspects of rehearsal in the absence of working memory, we asked the subjects to repeatedly read subvocally six or one letters at a rate that approximated the internally generated rehearsal of working memory (motoric rehearsal task). For both tasks, bilateral regions of the superior cerebellar hemispheres (left superior HVIIA and right HVI) and portions of posterior vermis (VI and superior VIIA) exhibited increased activation during high relative to low load conditions. In contrast, the right inferior cerebellar hemisphere (HVIIB) exhibited this load effect only during the working-memory task. We hypothesize that HVI and superior HVIIA activation represents input from the articulatory control system of working memory from the frontal lobes and that HVIIB activation is derived from the phonological store in temporal and parietal regions. From these inputs, the cerebellum could compute the discrepancy between actual and intended phonological rehearsal and use this information to update a feedforward command to the frontal lobes, thereby facilitating the phonological loop.

    View details for Web of Science ID A1997YK82200028

    View details for PubMedID 9391022

  • Semantic repetition priming for verbal and pictorial knowledge: A functional MRI study of left inferior prefrontal cortex JOURNAL OF COGNITIVE NEUROSCIENCE Wagner, A. D., Desmond, J. E., Demb, J. B., Glover, G. H., Gabrieli, J. D. 1997; 9 (6): 714-726

    Abstract

    Functional neuroimaging studies of single-word processing have demonstrated decreased activation in left inferior prefrontal cortex (LIPC) during repeated semantic processing relative to initial semantic processing. This item-specific memory effect occurs under implicit test instructions and represents word-toword semantic repetition priming. The present study examined the stimulus generality of LIPC function by measuring prefrontal cortical activation during repeated relative to initial semantic processing of words (word-to-word semantic repetition priming) and of pictures (picture-to-picture semantic repetition priming). For both words and pictures, LIPC activation decreased with repetition, suggesting that this area subserves semantic analysis of stimuli regardless of perceptual form. Decreased activation was greater in extent for words than for pictures. The LIPC area may act as a semantic executive system that mediates on-line retrieval of long-term conceptual knowledge necessary for guiding task performance.

    View details for Web of Science ID 000071078700002

    View details for PubMedID 23964594

  • Functional magnetic resonance imaging of semantic memory processes in the frontal lobes PSYCHOLOGICAL SCIENCE Gabrieli, J. D., Desmond, J. E., Demb, J. B., Wagner, A. D., Stone, M. V., Vaidya, C. J., Glover, G. H. 1996; 7 (5): 278-283
  • Does recoding interfering material improve recall? JOURNAL OF EXPERIMENTAL PSYCHOLOGY-LEARNING MEMORY AND COGNITION Bower, G. H., Wagner, A. D., Newman, S. E., Randle, J. D., Hodges, M. J. 1996; 22 (1): 240-245

    Abstract

    In 4 experiments, the authors attempted to replicate an improvement in recall of target memories produced by a post-learning clue enabling participants to reorganize and segregate interfering material, as shown by G. H. Bower and T. Mann (1992). The 1st three experiments studied retroactive interference (RI) in free recall of an initial word list after participants were informed post-learning of a way to categorize a second, interfering list. In each case, the reorganizing clue failed to reduce RI. In the 4th experiment, interference during serial recall of an initial list of letters from a 2nd list was examined. Again, the reorganizing clue given after learning failed to reduce RI. Clearly, if the post-information effect is genuine, then better experimental arrangements will be required to demonstrate it more reliably.

    View details for Web of Science ID A1996TT57200015

    View details for PubMedID 8648287

  • Functional MRI measurement of language lateralization in Wada-tested patients BRAIN Desmond, J. E., Sum, J. M., Wagner, A. D., Demb, J. B., Shear, P. K., Glover, G. H., Gabrieli, J. D., Morrell, M. J. 1995; 118: 1411-1419

    Abstract

    In this study the use of functional MRI (fMRI) for measuring language lateralization non-invasively was examined. The subjects were seven patients with histories of temporal lobe epilepsy who had undergone Wada testing for pre-surgical evaluation. Four patients were left-hemisphere-dominant and three were right-hemisphere-dominant for language. They received fMRI scans while they made semantic or perceptual judgments about visually presented words. Regions of the inferior frontal gyrus (pars triangularis and pars orbitalis) and neighbouring orbital cortex, corresponding to portions of Brodmann areas 45, 46 and 47, exhibited significant increases in activation during semantic relative to perceptual judgments. Lateralization of the increases in activation were consistent with the Wada test assessments of hemispheric language dominance in each of the seven patients. These results suggest that, in addition to providing a tool for investigating human cognitive processes, fMRI has significant clinical potential as a non-invasive measure of language lateralization.

    View details for Web of Science ID A1995TQ33300004

    View details for PubMedID 8595473

  • SEMANTIC ENCODING AND RETRIEVAL IN THE LEFT INFERIOR PREFRONTAL CORTEX - A FUNCTIONAL MRI STUDY OF TASK-DIFFICULTY AND PROCESS SPECIFICITY JOURNAL OF NEUROSCIENCE Demb, J. B., Desmond, J. E., Wagner, A. D., Vaidya, C. J., Glover, G. H., Gabrieli, J. D. 1995; 15 (9): 5870-5878

    Abstract

    Prefrontal cortical function was examined during semantic encoding and repetition priming using functional magnetic resonance imaging (fMRI), a noninvasive technique for localizing regional changes in blood oxygenation, a correlate of neural activity. Words studied in a semantic (deep) encoding condition were better remembered than words studied in both easier and more difficult nonsemantic (shallow) encoding conditions, with difficulty indexed by response time. The left inferior prefrontal cortex (LIPC) (Brodmann's areas 45, 46, 47) showed increased activation during semantic encoding relative to nonsemantic encoding regardless of the relative difficulty of the nonsemantic encoding task. Therefore, LIPC activation appears to be related to semantic encoding and not task difficulty. Semantic encoding decisions are performed faster the second time words are presented. This represents semantic repetition priming, a facilitation in semantic processing for previously encoded words that is not dependent on intentional recollection. The same LIPC area activated during semantic encoding showed decreased activation during repeated semantic encoding relative to initial semantic encoding of the same words. This decrease in activation during repeated encoding was process specific; it occurred when words were semantically reprocessed but not when words were nonsemantically reprocessed. The results were apparent in both individual and averaged functional maps. These findings suggest that the LIPC is part of a semantic executive system that contributes to the on-line retrieval of semantic information.

    View details for Web of Science ID A1995RU10800002

    View details for PubMedID 7666172

Conference Proceedings


  • Dissociations between familiarity processes in explicit recognition and implicit perceptual memory Wagner, A. D., Gabrieli, J. D., Verfaellie, M. AMER PSYCHOLOGICAL ASSOC. 1997: 305-323

    Abstract

    Dual-process theories of recognition posit that a perceptual familiarity process contributes to both explicit recognition and implicit perceptual memory. This putative single familiarity process has been indexed by inclusion-exclusion, remember-know, and repetition priming measures. The present studies examined whether these measures identify a common familiarity process. Familiarity-based explicit recognition (as indexed by the inclusion-exclusion and the independence remember-know procedures) increased with conceptual processing. In contrast, implicit word-identification priming and familiarity-based word-stem completion (as indexed by inclusion-exclusion) increased with study-test perceptual similarity. These dissociations indicate that familiarity-based explicit recognition may be more sensitive to conceptual than to perceptual processing and is functionally distinct from the perceptual familiarity process mediating implicit perceptual memory.

    View details for Web of Science ID A1997WP84700003

    View details for PubMedID 9080006

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