Bio

Professional Education


  • Doctor of Philosophy, S.U.N.Y. State University at Stony Brook (2009)
  • Bachelor of Engineering, Shanghai Jiaotong University (2000)
  • Master of Science, Peking University (2004)

Stanford Advisors


Publications

Journal Articles


  • Proactive Selective Response Suppression Is Implemented via the Basal Ganglia JOURNAL OF NEUROSCIENCE Majid, D. S., Cai, W., Corey-Bloom, J., Aron, A. R. 2013; 33 (33): 13259-13269

    Abstract

    In the welter of everyday life, people can stop particular response tendencies without affecting others. A key requirement for such selective suppression is that subjects know in advance which responses need stopping. We hypothesized that proactively setting up and implementing selective suppression relies on the basal ganglia and, specifically, regions consistent with the inhibitory indirect pathway for which there is scant functional evidence in humans. Consistent with this hypothesis, we show, first, that the degree of proactive motor suppression when preparing to stop selectively (indexed by transcranial magnetic stimulation) corresponds to striatal, pallidal, and frontal activation (indexed by functional MRI). Second, we demonstrate that greater striatal activation at the time of selective stopping correlates with greater behavioral selectivity. Third, we show that people with striatal and pallidal volume reductions (those with premanifest Huntington's disease) have both absent proactive motor suppression and impaired behavioral selectivity when stopping. Thus, stopping goals are used to proactively set up specific basal ganglia channels that may then be triggered to implement selective suppression. By linking this suppression to the striatum and pallidum, these results provide compelling functional evidence in humans of the basal ganglia's inhibitory indirect pathway.

    View details for DOI 10.1523/JNEUROSCI.5651-12.2013

    View details for Web of Science ID 000323155700002

    View details for PubMedID 23946385

  • The role of the right presupplementary motor area in stopping action: two studies with event-related transcranial magnetic stimulation JOURNAL OF NEUROPHYSIOLOGY Cai, W., George, J. S., Verbruggen, F., Chambers, C. D., Aron, A. R. 2012; 108 (2): 380-389

    Abstract

    Rapidly stopping action engages a network in the brain including the right presupplementary motor area (preSMA), the right inferior frontal gyrus, and the basal ganglia. Yet the functional role of these different regions within the overall network still remains unclear. Here we focused on the role of the right preSMA in behavioral stopping. We hypothesized that the underlying neurocognitive function of this region is one or more of setting up a stopping rule in advance, modulating response tendencies (e.g., slowing down in anticipation of stopping), and implementing stopping when the stop signal occurs. We performed two experiments with magnetic resonance imaging (MRI)-guided, event-related, transcranial magnetic stimulation(TMS), during the performance of variants of the stop signal task. In experiment 1 we show that stimulation of the right preSMA versus vertex (control site) slowed the implementation of stopping (measured via stop signal reaction time) but had no influence on modulation of response tendencies. In experiment 2, we showed that stimulation of the right preSMA slowed implementation of stopping in a mechanistically selective form of stopping but had no influence on setting up stopping rules. The results go beyond the replication of prior findings by showing that TMS of the right preSMA impairs stopping behavior (including a behaviorally selective form of stopping) through a specific disruption of the implementation of stopping. Future studies are required to establish whether this was due to stimulation of the right preSMA itself or because of remote effects on the wider stopping network.

    View details for DOI 10.1152/jn.00132.2012

    View details for Web of Science ID 000306416400002

    View details for PubMedID 22514296

  • Stimulating deep cortical structures with the batwing coil: How to determine the intensity for transcranial magnetic stimulation using coil-cortex distance JOURNAL OF NEUROSCIENCE METHODS Cai, W., George, J. S., Chambers, C. D., Stokes, M. G., Verbruggen, F., Aron, A. R. 2012; 204 (2): 238-241

    Abstract

    Transcranial magnetic stimulation (TMS) is increasingly used in cognitive neuroscience to probe non-motor cortical regions. A key question for such studies is the choice of stimulation intensity. Early studies used a simple metric such as 115% of motor threshold (MT) for non-motor regions; where MT is the stimulation intensity required to elicit a particular amplitude of motor evoked potential or visible muscle twitch when the coil is placed over primary motor cortex. Recently, however, it was demonstrated that this simple metric for stimulation of non-motor regions is inadequate - it could lead to over or under-stimulation depending on the distance between the coil and the cortex. Instead, a method was developed to scale the motor threshold based on coil-cortex distance, at least for standard figure-of-eight stimulating coils. Here we validate the same method for a 'batwing coil', which is designed to stimulate deeper cortical structures such as the medial frontal cortex. We modulated coil-cortex distance within-participant by inserting spacers of different thickness between coil and scalp. We then measured MT at each spacer. We show that for every millimeter between coil and scalp an additional 1.4% of TMS output is required to induce an equivalent level of brain stimulation at the motor cortex. Using this parameter we describe a linear function to adjust MT for future studies of non-motor regions-of-interest using the batwing coil. This is the first study to demonstrate the effects of coil-cortical distance on stimulation efficiency via a monophasic system using a batwing coil.

    View details for DOI 10.1016/j.jneumeth.2011.11.020

    View details for Web of Science ID 000301612700005

    View details for PubMedID 22138632

  • Stopping speech suppresses the task-irrelevant hand BRAIN AND LANGUAGE Cai, W., Oldenkamp, C. L., Aron, A. R. 2012; 120 (3): 412-415

    Abstract

    Some situations require one to quickly stop an initiated response. Recent evidence suggests that rapid stopping engages a mechanism that has diffuse effects on the motor system. For example, stopping the hand dampens the excitability of the task-irrelevant leg. However, it is unclear whether this 'global suppression' could apply across wider motor modalities. Here we tested whether stopping speech leads to suppression of the task-irrelevant hand. We used Transcranial Magnetic Stimulation over the primary motor cortex with concurrent electromyography from the hand. We found that when speech was successfully stopped the motor evoked potential from the task-irrelevant hand was significantly reduced compared to when the participant failed to stop speaking, or responded on non stop signal trials, or compared to baseline. This shows that when speech is quickly stopped, there is a broad suppression across the motor system. This has implications for the neural basis of speech control and stuttering.

    View details for DOI 10.1016/j.bandl.2011.11.006

    View details for Web of Science ID 000301759100022

    View details for PubMedID 22206872

  • Roles for the pre-supplementary motor area and the right inferior frontal gyrus in stopping action: Electrophysiological responses and functional and structural connectivity NEUROIMAGE Swann, N. C., Cai, W., Conner, C. R., Pieters, T. A., Claffey, M. P., George, J. S., Aron, A. R., Tandon, N. 2012; 59 (3): 2860-2870

    Abstract

    Both the pre-supplementary motor area (preSMA) and the right inferior frontal gyrus (rIFG) are important for stopping action outright. These regions are also engaged when preparing to stop. We aimed to elucidate the roles of these regions by harnessing the high spatio-temporal resolution of electrocorticography (ECoG), and by using a task that engages both preparing to stop and stopping outright. First, we validated the task using fMRI in 16 healthy control participants to confirm that both the preSMA and the rIFG were active. Next, we studied a rare patient with intracranial grid coverage of both these regions, using macrostimulation, diffusion tractography, cortico-cortical evoked potentials (CCEPs) and task-based ECoG. Macrostimulation of the preSMA induced behavioral motor arrest. Diffusion tractography revealed a structural connection between the preSMA and rIFG. CCEP analysis showed that stimulation of the preSMA evoked strong local field potentials within 30 ms in rIFG. During the task, when preparing to stop, there was increased high gamma amplitude (~70-250 Hz) in both regions, with preSMA preceding rIFG by ~750 ms. For outright stopping there was also a high gamma amplitude increase in both regions, again with preSMA preceding rIFG. Further, at the time of stopping, there was an increase in beta band activity (~16 Hz) in both regions, with significantly stronger inter-regional coherence for successful vs. unsuccessful stop trials. The results complement earlier reports of a structural/functional action control network between the preSMA and rIFG. They go further by revealing between-region timing differences in the high gamma band when preparing to stop and stopping outright. They also reveal strong between-region coherence in the beta band when stopping is successful. Implications for theories of action control are discussed.

    View details for DOI 10.1016/j.neuroimage.2011.09.049

    View details for Web of Science ID 000299494000085

    View details for PubMedID 21979383

  • Transcranial Magnetic Stimulation Reveals Dissociable Mechanisms for Global Versus Selective Corticomotor Suppression Underlying the Stopping of Action CEREBRAL CORTEX Majid, D. S., Cai, W., George, J. S., Verbruggen, F., Aron, A. R. 2012; 22 (2): 363-371

    Abstract

    Stopping an initiated response is an essential function, investigated in many studies with go/no-go and stop-signal paradigms. These standard tests require rapid action cancellation. This appears to be achieved by a suppression mechanism that has "global" effects on corticomotor excitability (i.e., affecting task-irrelevant muscles). By contrast, stopping action in everyday life may require selectivity (i.e., targeting a specific response tendency without affecting concurrent action). We hypothesized that while standard stopping engages global suppression, behaviorally selective stopping engages a selective suppression mechanism. Accordingly, we measured corticomotor excitability of the task-irrelevant leg using transcranial magnetic stimulation while subjects stopped the hand. Experiment 1 showed that for standard (i.e., nonselective) stopping, the task-irrelevant leg was suppressed. Experiment 2 showed that for behaviorally selective stopping, there was no mean leg suppression. Experiment 3 directly compared behaviorally nonselective and selective stopping. Leg suppression occurred only in the behaviorally nonselective condition. These results argue that global and selective suppression mechanisms are dissociable. Participants may use a global suppression mechanism when speed is stressed; however, they may recruit a more selective suppression mechanism when selective stopping is behaviorally necessary and preparatory information is available. We predict that different fronto-basal-ganglia pathways underpin these different suppression mechanisms.

    View details for DOI 10.1093/cercor/bhr112

    View details for Web of Science ID 000299124400011

    View details for PubMedID 21666129

  • Rule-Guided Executive Control of Response Inhibition: Functional Topography of the Inferior Frontal Cortex PLOS ONE Cai, W., Leung, H. 2011; 6 (6)

    Abstract

    The human inferior frontal cortex (IFC) is a large heterogeneous structure with distinct cytoarchitectonic subdivisions and fiber connections. It has been found involved in a wide range of executive control processes from target detection, rule retrieval to response control. Since these processes are often being studied separately, the functional organization of executive control processes within the IFC remains unclear.We conducted an fMRI study to examine the activities of the subdivisions of IFC during the presentation of a task cue (rule retrieval) and during the performance of a stop-signal task (requiring response generation and inhibition) in comparison to a not-stop task (requiring response generation but not inhibition). We utilized a mixed event-related and block design to separate brain activity in correspondence to transient control processes from rule-related and sustained control processes. We found differentiation in control processes within the IFC. Our findings reveal that the bilateral ventral-posterior IFC/anterior insula are more active on both successful and unsuccessful stop trials relative to not-stop trials, suggesting their potential role in the early stage of stopping such as triggering the stop process. Direct countermanding seems to be outside of the IFC. In contrast, the dorsal-posterior IFC/inferior frontal junction (IFJ) showed transient activity in correspondence to the infrequent presentation of the stop signal in both tasks and the left anterior IFC showed differential activity in response to the task cues. The IFC subdivisions also exhibited similar but distinct patterns of functional connectivity during response control.Our findings suggest that executive control processes are distributed across the IFC and that the different subdivisions of IFC may support different control operations through parallel cortico-cortical and cortico-striatal circuits.

    View details for DOI 10.1371/journal.pone.0020840

    View details for Web of Science ID 000291356400032

    View details for PubMedID 21673969

  • A Proactive Mechanism for Selective Suppression of Response Tendencies JOURNAL OF NEUROSCIENCE Cai, W., Oldenkamp, C. L., Aron, A. R. 2011; 31 (16): 5965-5969

    Abstract

    While most research on stopping action examines how an initiated response is stopped when a signal occurs (i.e., reactively), everyday life also calls for a mechanism to prepare to stop a particular response tendency (i.e., proactively and selectively). We hypothesized that human subjects can prepare to stop a particular response by proactively suppressing that response representation in the brain. We tested this by using single-pulse transcranial magnetic stimulation and concurrent electromyography. This allowed us to interrogate the corticomotor excitability of specific response representations even before action ensued. We found that the motor evoked potential of the effector that might need to be stopped in the future was significantly reduced compared with when that effector was at rest. Further, this neural index of proactive and selective suppression predicted the subsequent selectivity with which the behavioral response was stopped. These results go further than earlier reports of reduced motor excitability when responses are stopped. They show that the control can be applied in advance (proactively) and also targeted at a particular response channel (selectively). This provides novel evidence for an active mechanism of suppression in the brain that is setup according to the subject's goals and even before action ensues.

    View details for DOI 10.1523/JNEUROSCI.6292-10.2011

    View details for Web of Science ID 000289769400010

    View details for PubMedID 21508221

  • Deep Brain Stimulation of the Subthalamic Nucleus Alters the Cortical Profile of Response Inhibition in the Beta Frequency Band: A Scalp EEG Study in Parkinson's Disease JOURNAL OF NEUROSCIENCE Swann, N., Poizner, H., Houser, M., Gould, S., Greenhouse, I., Cai, W., Strunk, J., George, J., Aron, A. R. 2011; 31 (15): 5721-5729

    Abstract

    Stopping an initiated response could be implemented by a fronto-basal-ganglia circuit, including the right inferior frontal cortex (rIFC) and the subthalamic nucleus (STN). Intracranial recording studies in humans reveal an increase in beta-band power (approximately 16-20 Hz) within the rIFC and STN when a response is stopped. This suggests that the beta-band could be important for communication in this network. If this is the case, then altering one region should affect the electrophysiological response at the other. We addressed this hypothesis by recording scalp EEG during a stop task while modulating STN activity with deep brain stimulation. We studied 15 human patients with Parkinson's disease and 15 matched healthy control subjects. Behaviorally, patients OFF stimulation were slower than controls to stop their response. Moreover, stopping speed was improved for ON compared to OFF stimulation. For scalp EEG, there was greater beta power, around the time of stopping, for patients ON compared to OFF stimulation. This effect was stronger over the right compared to left frontal cortex, consistent with the putative right lateralization of the stopping network. Thus, deep brain stimulation of the STN improved behavioral stopping performance and increased the beta-band response over the right frontal cortex. These results complement other evidence for a structurally connected functional circuit between right frontal cortex and the basal ganglia. The results also suggest that deep brain stimulation of the STN may improve task performance by increasing the fidelity of information transfer within a fronto-basal-ganglia circuit.

    View details for DOI 10.1523/JNEUROSCI.6135-10.2011

    View details for Web of Science ID 000289472400021

    View details for PubMedID 21490213

  • Cortical activity during manual response inhibition guided by color and orientation cues BRAIN RESEARCH Cai, W., Leung, H. 2009; 1261: 20-28

    Abstract

    It has been suggested that the right inferior frontal gyrus (IFG) plays a critical role in manual response inhibition, although neuroimaging studies of healthy adults have also reported widespread activations in other cortical regions during a variety of response inhibition tasks. We conducted a functional magnetic resonance imaging (fMRI) experiment to examine whether the activation of the IFG is dependent on the type of visuo-motor associations during response inhibition by varying the feature of the stop signal (color vs. orientation) in the stop-signal task. Results from 12 subjects showed that the bilateral ventral posterior IFG, anterior insula, inferior frontal junction (IFJ), middle temporal gyrus (MTG) and fusiform gyrus (FG) are active during response inhibition cued by both color and orientation stop signals. While only the MTG showed differential activity to the two stop signals, both MTG and FG showed significantly stronger activity during successful than unsuccessful stopping of unwanted responses cued by orientation and color, respectively. Our findings suggest that the right ventral posterior IFG may play a more general role in response inhibition regardless of the feature of the visual signal, while successful inhibition may depend on efficient processing of the signal.

    View details for DOI 10.1016/j.brainres.2008.12.073

    View details for Web of Science ID 000264693300003

    View details for PubMedID 19401178

  • Common and differential ventrolateral prefrontal activity during inhibition of hand and eye movements JOURNAL OF NEUROSCIENCE Leung, H., Cai, W. 2007; 27 (37): 9893-9900

    Abstract

    The inferior frontal cortex, particularly the ventrolateral prefrontal cortex (VLPFC) in the right hemisphere, has been implicated to serve as a general inhibitory mechanism in the cognitive control of behavior. Because this notion was primarily based on studies of response inhibition in manual tasks, it has yet to be validated in other response modalities. We conducted a functional magnetic resonance imaging study to examine whether the VLPFC is commonly activated during inhibition of responses by hand and by eye within the same subjects. We used the stop-signal task, a relatively pure measure of response inhibition, as the behavioral paradigm. Results from 12 subjects showed that both the right and the left caudal VLPFC and anterior insula, rostral to the premotor area, are activated during inhibition of both manual and saccadic responses. Within the posterior VLPFC, activations overlapped to a significant extent across the two response modalities, although a weaker functionally differentiation was also found along the dorsoventral axis. Other areas such as medial superior frontal gyrus (pre-supplementary motor area/supplementary eye field), dorsolateral prefrontal cortex, and inferior parietal cortex were also activated during canceling both hand and eye movements. Our findings suggest that a common VLPFC network is involved in response inhibition, although the specific control of the different response modalities may be partially segregated within the lateral prefrontal cortex.

    View details for DOI 10.1523/JNEUROSCI.2837-07.2007

    View details for Web of Science ID 000249415000010

    View details for PubMedID 17855604

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