Bio

Honors & Awards


  • Dean's Postdoctoral Fellowship, School of Medicine, Stanford University (2012)
  • Gatsby-COSYNE Travel Fellowship, Computational and Systems Neuroscience (COSYNE) Meeting, Salt Lake City, Utah (2010)
  • Human Brain Mapping Travel Award and Bio-X Travel Award, National Institutes of Health/Stanford University (2007)
  • Stanford Graduate (Smith) Fellowship, Stanford University (2004-2007)
  • President of India Gold Medal, Indian Institute of Technology (IIT), Madras, India (2004)

Professional Education


  • Master of Technology, Indian Institute of Technology, Madras, Aerospace Engineering (2004)
  • Bachelor of Technology, Indian Institute of Technology, Madras, Aerospace Enginneering (2004)
  • Doctor of Philosophy, Stanford University, NEURS-PHD (2011)

Stanford Advisors


Research & Scholarship

Current Research and Scholarly Interests


Attention promotes intelligent, adaptive behaviors by enabling the selective processing of the most relevant information. I am interested in understanding how gamma-band (25-140Hz) oscillations in brain networks contribute to attention behaviors. I study these oscillations in the avian optic tectum (superior colliculus), a midbrain structure involved in attention, spatial vision and gaze control with a combination of electrophysiology (in/ex-vivo), computational modeling, and psychophysics.

Lab Affiliations


Publications

Journal Articles


  • Visuospatial selective attention in chickens. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES Sridharan, D., Ramamurthy, D. L., Schwarz, J. S., Knudsen, E. I. 2014
  • Selective attention in birds CURRENT BIOLOGY Sridharan, D., Schwarz, J. S., Knudsen, E. I. 2014
  • Magnetic tracking of eye position in freely behaving chickens. FRONTIERS IN SYSTEMS NEUROSCIENCE Schwarz, J. S., Sridharan, D., Knudsen, E. I. 2013; 7: 91

    View details for DOI 10.3389/fnsys.2013.00091

  • Spatial probability dynamically modulates visual target detection in chickens. PloS one Sridharan, D., Ramamurthy, D. L., Knudsen, E. I. 2013; 8 (5): e64136

    Abstract

    The natural world contains a rich and ever-changing landscape of sensory information. To survive, an organism must be able to flexibly and rapidly locate the most relevant sources of information at any time. Humans and non-human primates exploit regularities in the spatial distribution of relevant stimuli (targets) to improve detection at locations of high target probability. Is the ability to flexibly modify behavior based on visual experience unique to primates? Chickens (Gallus domesticus) were trained on a multiple alternative Go/NoGo task to detect a small, briefly-flashed dot (target) in each of the quadrants of the visual field. When targets were presented with equal probability (25%) in each quadrant, chickens exhibited a distinct advantage for detecting targets at lower, relative to upper, hemifield locations. Increasing the probability of presentation in the upper hemifield locations (to 80%) dramatically improved detection performance at these locations to be on par with lower hemifield performance. Finally, detection performance in the upper hemifield changed on a rapid timescale, improving with successive target detections, and declining with successive detections at the diagonally opposite location in the lower hemifield. These data indicate the action of a process that in chickens, as in primates, flexibly and dynamically modulates detection performance based on the spatial probabilities of sensory stimuli as well as on recent performance history.

    View details for PubMedID 23734188

  • Gamma Oscillations Are Generated Locally in an Attention-Related Midbrain Network NEURON Goddard, C. A., Sridharan, D., Huguenard, J. R., Knudsen, E. I. 2012; 73 (3): 567-580

    Abstract

    Gamma-band (25-140 Hz) oscillations are a hallmark of sensory processing in the forebrain. The optic tectum (OT), a midbrain structure implicated in sensorimotor processing and attention, also exhibits gamma oscillations. However, the origin and mechanisms of these oscillations remain unknown. We discovered that in acute slices of the avian OT, persistent (>100 ms) epochs of large amplitude gamma oscillations can be evoked that closely resemble those recorded in vivo. We found that cholinergic, glutamatergic, and GABAergic mechanisms differentially regulate the structure of the oscillations at various timescales. These persistent oscillations originate in the multisensory layers of the OT and are broadcast to visual layers via the cholinergic nucleus Ipc, providing a potential mechanism for enhancing the processing of visual information within the OT. The finding that the midbrain contains an intrinsic gamma-generating circuit suggests that the OT could use its own oscillatory code to route signals to forebrain networks.

    View details for DOI 10.1016/j.neuron.2011.11.028

    View details for Web of Science ID 000300140600016

    View details for PubMedID 22325207

  • Space coding by gamma oscillations in the barn owl optic tectum JOURNAL OF NEUROPHYSIOLOGY Sridharan, D., Boahen, K., Knudsen, E. I. 2011; 105 (5): 2005-2017

    Abstract

    Gamma-band (25-140 Hz) oscillations of the local field potential (LFP) are evoked by sensory stimuli in the mammalian forebrain and may be strongly modulated in amplitude when animals attend to these stimuli. The optic tectum (OT) is a midbrain structure known to contribute to multimodal sensory processing, gaze control, and attention. We found that presentation of spatially localized stimuli, either visual or auditory, evoked robust gamma oscillations with distinctive properties in the superficial (visual) layers and in the deep (multimodal) layers of the owl's OT. Across layers, gamma power was tuned sharply for stimulus location and represented space topographically. In the superficial layers, induced LFP power peaked strongly in the low-gamma band (25-90 Hz) and increased gradually with visual contrast across a wide range of contrasts. Spikes recorded in these layers included presumptive axonal (input) spikes that encoded stimulus properties nearly identically with gamma oscillations and were tightly phase locked with the oscillations, suggesting that they contribute to the LFP oscillations. In the deep layers, induced LFP power was distributed across the low and high (90-140 Hz) gamma-bands and tended to reach its maximum value at relatively low visual contrasts. In these layers, gamma power was more sharply tuned for stimulus location, on average, than were somatic spike rates, and somatic spikes synchronized with gamma oscillations. Such gamma synchronized discharges of deep-layer neurons could provide a high-resolution temporal code for signaling the location of salient sensory stimuli.

    View details for DOI 10.1152/jn.00965.2010

    View details for Web of Science ID 000290710300006

    View details for PubMedID 21325681

  • A critical role for the right fronto-insular cortex in switching between central-executive and default-mode networks PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Sridharan, D., Levitin, D. J., Menon, V. 2008; 105 (34): 12569-12574

    Abstract

    Cognitively demanding tasks that evoke activation in the brain's central-executive network (CEN) have been consistently shown to evoke decreased activation (deactivation) in the default-mode network (DMN). The neural mechanisms underlying this switch between activation and deactivation of large-scale brain networks remain completely unknown. Here, we use functional magnetic resonance imaging (fMRI) to investigate the mechanisms underlying switching of brain networks in three different experiments. We first examined this switching process in an auditory event segmentation task. We observed significant activation of the CEN and deactivation of the DMN, along with activation of a third network comprising the right fronto-insular cortex (rFIC) and anterior cingulate cortex (ACC), when participants perceived salient auditory event boundaries. Using chronometric techniques and Granger causality analysis, we show that the rFIC-ACC network, and the rFIC, in particular, plays a critical and causal role in switching between the CEN and the DMN. We replicated this causal connectivity pattern in two additional experiments: (i) a visual attention "oddball" task and (ii) a task-free resting state. These results indicate that the rFIC is likely to play a major role in switching between distinct brain networks across task paradigms and stimulus modalities. Our findings have important implications for a unified view of network mechanisms underlying both exogenous and endogenous cognitive control.

    View details for DOI 10.1073/pnas.0800005105

    View details for Web of Science ID 000258905700084

    View details for PubMedID 18723676

  • An in-silico model of dynamic routing through neuronal coherence Advances in Neural Information Processing Systems Sridharan D, Percival B, Arthur J, Boahen K 2008; 20: 1401-1408
  • Neural dynamics of event segmentation in music: Converging evidence for dissociable ventral and dorsal networks NEURON Sridharan, D., Levitin, D. J., Chafe, C. H., Berger, J., Menon, V. 2007; 55 (3): 521-532

    Abstract

    The real world presents our sensory systems with a continuous stream of undifferentiated information. Segmentation of this stream at event boundaries is necessary for object identification and feature extraction. Here, we investigate the neural dynamics of event segmentation in entire musical symphonies under natural listening conditions. We isolated time-dependent sequences of brain responses in a 10 s window surrounding transitions between movements of symphonic works. A strikingly right-lateralized network of brain regions showed peak response during the movement transitions when, paradoxically, there was no physical stimulus. Model-dependent and model-free analysis techniques provided converging evidence for activity in two distinct functional networks at the movement transition: a ventral fronto-temporal network associated with detecting salient events, followed in time by a dorsal fronto-parietal network associated with maintaining attention and updating working memory. Our study provides direct experimental evidence for dissociable and causally linked ventral and dorsal networks during event segmentation of ecologically valid auditory stimuli.

    View details for DOI 10.1016/j.neuron.2007.07.003

    View details for Web of Science ID 000248711000017

    View details for PubMedID 17678862

  • The role of the basal ganglia in exploration in a neural model based on reinforcement learning INTERNATIONAL JOURNAL OF NEURAL SYSTEMS Sridharan, D., Prashanth, P. S., Chakravarthy, V. S. 2006; 16 (2): 111-124

    Abstract

    We present a computational model of basal ganglia as a key player in exploratory behavior. The model describes exploration of a virtual rat in a simulated water pool experiment. The virtual rat is trained using a reward-based or reinforcement learning paradigm which requires units with stochastic behavior for exploration of the system's state space. We model the Subthalamic Nucleus-Globus Pallidus externa (STN-GPe) segment of the basal ganglia as a pair of neuronal layers with oscillatory dynamics, exhibiting a variety of dynamic regimes such as chaos, traveling waves and clustering. Invoking the property of chaotic systems to explore state-space, we suggest that the complex exploratory dynamics of STN-GPe system in conjunction with dopamine-based reward signaling from the Substantia Nigra pars compacta (SNc) present the two key ingredients of a reinforcement learning system.

    View details for Web of Science ID 000237787200003

    View details for PubMedID 16688851

Presentations


  • Towards a mechanistic understanding of the role of gamma oscillations in attention: An avian midbrain model (SfN Nanosymposium, contributed talk)

    Nanosymposium on Functional Mechanisms of Attention by Animal.

    Time Period

    11/14/2011

    Presented To

    Society for Neuroscience (SfN, 41st annual meeting)

    Location

    Washington DC, USA

  • Robust spatial working memory through inhibitory gamma synchrony (COSYNE, contributed talk) Kwabena Boahen, Sebastian Millner

    Time Period

    February 10, 2010

    Presented To

    Computational and Systems Neuroscience (COSYNE)

    Location

    Salt Lake City, Utah, USA

    Collaborators

  • A causal role for the right fronto-insular cortex in switching between executive-control and default-mode networks. (OHBM, contributed talk) Vinod Menon

    Time Period

    June 10, 2007

    Presented To

    Organization for Human Brain Mapping (OHBM, 13th annual meeting)

    Location

    Chicago, USA

    Collaborators

    • Vinod Menon, Professor (Research) of Psychiatry and Behavioral Sciences
  • The neuroscience of music perception explored through functional imaging and computational modeling (SICA, invited talk)

    Time Period

    5/13/2007

    Presented To

    2nd Annual Stanford Symposium on Music, Rhythm and the Brain organized by the Stanford Institute for Creativity and the Arts

    Location

    Stanford, CA

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