Alapakkam Sampath, Ph.D.

Research interest:

Research

Dr. Sampath is an internationally known visual neuroscientist who is recognized as a leader in the study of cellular and circuit level visual processing. His work focuses on signal transmission between photoreceptor cells, the rods and cones, and bipolar cells to determine how information is processed within retinal circuits and gives rise to visual perceptual sensitivity. Not only is his work of broad fundamental scientific interest, it has significant implications for our understanding of visual blinding diseases such as night blindness.

Publications

Majumder Anurima, Pahlberg Johan, Boyd Kimberly K, Kerov Vasily, Kolandaivelu Saravanan, Ramamurthy Visvanathan, Sampath Alapakkam P, Artemyev Nikolai O Transducin translocation contributes to rod survival and enhances synaptic transmission from rods to rod bipolar cells Proceedings of the National Academy of Sciences of the United States of America, 2013; 110(30): 12468-73.

Chen Shih-Kuo, Chew Kylie S, McNeill David S, Keeley Patrick W, Ecker Jennifer L, Mao Buqing Q, Pahlberg Johan, Kim Bright, Lee Sammy C S, Fox Michael A, Guido William, Wong Kwoon Y, Sampath Alapakkam P, Reese Benjamin E, Kuruvilla Rejji, Hattar Samer Apoptosis regulates ipRGC spacing necessary for rods and cones to drive circadian photoentrainment Neuron, 2013; 77(3): 503-15.

Mao Wen, Miyagishima K J, Yao Yun, Soreghan Brian, Sampath Alapakkam P, Chen Jeannie Functional comparison of rod and cone Gα(t) on the regulation of light sensitivity The Journal of biological chemistry, 2013; 288(8): 5257-67.

Arman A Cyrus, Sampath Alapakkam P Dark-adapted response threshold of OFF ganglion cells is not set by OFF bipolar cells in the mouse retina Journal of neurophysiology, 2012; 107(10): 2649-59.

Cho Alice K, Sampath Alapakkam P, Weiland James D Physiological response of normal and RD mouse retinal ganglion cells to electrical stimulation Conference proceedings : … Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, 2012; 2012(10): 2985-8.

Cao Yan, Pahlberg Johan, Sarria Ignacio, Kamasawa Naomi, Sampath Alapakkam P, Martemyanov Kirill A Regulators of G protein signaling RGS7 and RGS11 determine the onset of the light response in ON bipolar neurons Proceedings of the National Academy of Sciences of the United States of America, 2012; 109(20): 7905-10.

Farley Robert A, Sampath Alapakkam P Perspectives on: information coding in mammalian sensory physiology The Journal of general physiology, 2011; 138(3): 281-2.

Doroudchi M Mehdi, Greenberg Kenneth P, Liu Jianwen, Silka Kimberly A, Boyden Edward S, Lockridge Jennifer A, Arman A Cyrus, Janani Ramesh, Boye Shannon E, Boye Sanford L, Gordon Gabriel M, Matteo Benjamin C, Sampath Alapakkam P, Hauswirth William W, Horsager Alan Virally delivered channelrhodopsin-2 safely and effectively restores visual function in multiple mouse models of blindness Molecular therapy : the journal of the American Society of Gene Therapy, 2011; 19(7): 1220-9.

Pahlberg Johan, Sampath Alapakkam P Visual threshold is set by linear and nonlinear mechanisms in the retina that mitigate noise: how neural circuits in the retina improve the signal-to-noise ratio of the single-photon response BioEssays : news and reviews in molecular, cellular and developmental biology, 2011; 33(6): 438-47.

Okawa Haruhisa, Pahlberg Johan, Rieke Fred, Birnbaumer Lutz, Sampath Alapakkam P Coordinated control of sensitivity by two splice variants of Gα(o) in retinal ON bipolar cells The Journal of general physiology, 2010; 136(4): 443-54.

Altimus Cara M, Güler Ali D, Alam Nazia M, Arman A Cyrus, Prusky Glen T, Sampath Alapakkam P, Hattar Samer Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities Nature neuroscience, 2010; 13(9): 1107-12.

Okawa Haruhisa, Miyagishima K Joshua, Arman A Cyrus, Hurley James B, Field Greg D, Sampath Alapakkam P Optimal processing of photoreceptor signals is required to maximize behavioural sensitivity The Journal of physiology, 2010; 588(Pt 11): 1947-60.

Matthews Hugh R, Sampath Alapakkam P Photopigment quenching is Ca2+ dependent and controls response duration in salamander L-cone photoreceptors The Journal of general physiology, 2010; 135(4): 355-66.

Singer Joshua H, Glowatzki Elisabeth, Moser Tobias, Strowbridge Ben W, Bhandawat Vikas, Sampath Alapakkam P Functional properties of synaptic transmission in primary sense organs The Journal of neuroscience : the official journal of the Society for Neuroscience, 2009; 29(41): 12802-6.

Miyagishima Kiyoharu J, Cornwall M Carter, Sampath Alapakkam P Metabolic constraints on the recovery of sensitivity after visual pigment bleaching in retinal rods The Journal of general physiology, 2009; 134(3): 165-75.

Mayank Mehta, Ph.D.

Research

The mind is thought to be the emergent property of the activities of ensembles of neurons. The nature of these emergent properties and how they arise are unknown. This is the focus of our research. In particular, our current research addresses the following fundamental questions in Neurophysics: 1. How is information about the physical world represented by ensembles of neurons? In particular, what are the neural mechanisms of perceiving space-time? 2. How do the neural representations evolve with learning? 3. What is the role of brain rhythms in learning and memory? 4. How does sleep influence learning? To address these questions we use both experimental and theoretical approaches as follows: 1. Develop hardware to measure and manipulate neural activity and behavior. 2. Measure the activity of ensembles of well isolated neurons from many hippocampal and neocortical areas simultaneously during learning and during sleep. 3. Develop data analysis tools to decipher the patterns of neural activity and field potentials, and their relationship to behavior. 4. Develop biophysical theories of synapses, neurons and neuronal networks that can explain these experimental finding, relate them to the underlying cellular mechanisms, and make experimentally testable predictions. The results would not only provide fundamental understanding of neural ensemble dynamics but also point to novel ways of treating learning and memory disorders.

Publications

Jason J. Moore, Pascal M. Ravassard, David Ho, Lavanya Acharya, Ashley L. Kees, Cliff Vuong, Mayanak R. Mehta.  Dynamics of Cortical Dendritic Membrane Potential and Spikes in Freely Behaving Cats.  Science, vol 335, issue 6331, 1281 (2017), 24 March 2017.

Acharya Lavanya, Aghajan Zahra M, Vuong Cliff, Moore Jason J, Mehta Mayank R Causal Influence of Visual Cues on Hippocampal Directional Selectivity Cell, 2016; 164(1-2): 197-207.

Mehta Mayank R From synaptic plasticity to spatial maps and sequence learning Hippocampus, 2015; 25(6): 756-62.

Aghajan Zahra M, Acharya Lavanya, Moore Jason J, Cushman Jesse D, Vuong Cliff, Mehta Mayank R Impaired spatial selectivity and intact phase precession in two-dimensional virtual reality Nature neuroscience, 2015; 18(1): 121-8.

Ravassard Pascal, Kees Ashley, Willers Bernard, Ho David, Aharoni Daniel, Cushman Jesse, Aghajan Zahra M, Mehta Mayank R Multisensory control of hippocampal spatiotemporal selectivity Science (New York, N.Y.), 2013; 340(6138): 1342-6.

Cushman Jesse D, Aharoni Daniel B, Willers Bernard, Ravassard Pascal, Kees Ashley, Vuong Cliff, Popeney Briana, Arisaka Katsushi, Mehta Mayank R Multisensory control of multimodal behavior: do the legs know what the tongue is doing? PloS one, 2013; 8(11): e80465.

Ghorbani Maryam, Mehta Mayank, Bruinsma Robijn, Levine Alex J Nonlinear-dynamics theory of up-down transitions in neocortical neural networks Physical review. E, Statistical, nonlinear, and soft matter physics, 2012; 85(2 Pt 1): 021908.

Ahmed Omar J, Mehta Mayank R Running speed alters the frequency of hippocampal gamma oscillations The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012; 32(21): 7373-83.

Hahn Thomas T G, McFarland James M, Berberich Sven, Sakmann Bert, Mehta Mayank R Spontaneous persistent activity in entorhinal cortex modulates cortico-hippocampal interaction in vivo Nature neuroscience, 2012; 15(11): 1531-8.

Resnik Evgeny, McFarland James M, Sprengel Rolf, Sakmann Bert, Mehta Mayank R The effects of GluA1 deletion on the hippocampal population code for position The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012; 32(26): 8952-68.

Mehta Mayank R Contribution of Ih to LTP, place cells, and grid cells Cell, 2011; 147(5): 968-70.

McFarland James M, Hahn Thomas T G, Mehta Mayank R Explicit-duration hidden Markov model inference of UP-DOWN states from continuous signals PloS one, 2011; 6(6): e21606.

Kumar Arvind, Mehta Mayank R Frequency-Dependent Changes in NMDAR-Dependent Synaptic Plasticity Frontiers in computational neuroscience, 2011; 5(5): 38.

Chen Zhiping, Resnik Evgeny, McFarland James M, Sakmann Bert, Mehta Mayank R Speed controls the amplitude and timing of the hippocampal gamma rhythm PloS one, 2011; 6(6): e21408.

Ahmed Omar J, Mehta Mayank R The hippocampal rate code: anatomy, physiology and theory Trends in neurosciences, 2009; 32(6): 329-38. Mehta Mayank R Cortico-hippocampal interaction during up-down states and memory consolidation Nature neuroscience, 2007; 10(1): 13-5.

Hahn Thomas T G, Sakmann Bert, Mehta Mayank R Differential responses of hippocampal subfields to cortical up-down states Proceedings of the National Academy of Sciences of the United States of America, 2007; 104(12): 5169-74.

Hoffman Kari L, Battaglia Francesco P, Harris Kenneth, MacLean Jason N, Marshall Lisa, Mehta Mayank R The upshot of up states in the neocortex: from slow oscillations to memory formation The Journal of neuroscience : the official journal of the Society for Neuroscience, 2007; 27(44): 11838-41.

Hahn Thomas T G, Sakmann Bert, Mehta Mayank R Phase-locking of hippocampal interneurons’ membrane potential to neocortical up-down states Nature neuroscience, 2006; 9(11): 1359-61.

Mehta Mayank R Role of rhythms in facilitating short-term memory Neuron, 2005; 45(1): 7-9.

Mehta Mayank R Cooperative LTP can map memory sequences on dendritic branches Trends in neurosciences, 2004; 27(2): 69-72.

Petersen Carl C H, Hahn Thomas T G, Mehta Mayank, Grinvald Amiram, Sakmann Bert Interaction of sensory responses with spontaneous depolarization in layer 2/3 barrel cortex Proceedings of the National Academy of Sciences of the United States of America, 2003; 100(23): 13638-43.