Dan Feldman
Assistant Professor of Biology, UCSD

e-mail: dfeldman@ucsd.edu

My laboratory is interested in how circuits in the cerebral cortex process and store information about the sensory environment. We focus on primary somatosensory (S1) cortex of the rat, which contains an orderly map of sensory input from the facial whiskers. The whisker map, like other sensory maps in the brain, is not fixed, but varies strongly with recent sensory experience. This phenomenon, called experience-dependent map plasticity, acts during development to transform immature circuits into appropriately organized connections that mediate adult sensory perception and sensory-guided behavior. In adults, such plasticity persists, and is thought to underlie certain forms of learning, and to contribute to recovery of function after stroke or peripheral injury. Though map plasticity occurs with common features across many brain regions, the cellular and synaptic mechanisms of map plasticity are largely unknown. A major focus of the lab’s work is to identify these mechanisms, and to understand how they drive information storage and optimization of cortical circuits. We are also interested in how S1 encodes and processes somatosensory input, and how plasticity and learning alter this processing.

Specific research topics:

Synaptic Mechanisms for Cortical Map Plasticity. Recent evidence suggests that long-term depression (LTD) at specific S1 synapses underlies a major component of whisker map plasticity, the activity-dependent loss of responses to deprived or underused inputs. We are currently testing this hypothesis by studying how sensory deprivation weakens S1 synapses, measured ex vivo in S1 slices from normal and whisker-deprived rats, and by testing whether novel pharmacological and genetic manipulations that selectively block LTD impair map plasticity in vivo. We are also attempting to identify additional sites and mechanisms of map plasticity, including long-term potentiation (LTP), alterations in S1 inhibitory circuirts, and anatomical changes in cortical microcircuits.

Mechanisms and Function of Spike Timing-Dependent Synaptic Plasticity. How experience induces LTP or LTD in vivo is unknown, and is central to theories of cortical plasticity. A major effort in the lab is to test an emerging model that millisecond-scale changes in the timing of presynaptic and postsynaptic spikes are the key induction signal for LTP and LTD in S1 in vivo. Such spike timing-dependent plasticity (STDP) is robust in S1 in vitro, and we showed recently that whisker deprivation acutely alters the timing of S1 spikes in vivo in a manner appropriate to drive LTD at relevant S1 synapses. We are now investigating how different patterns of whisker input generate different spike timing statistics at S1 synapses, thus leading to different forms of cortical plasticity. In other experiments, we are examining the detailed cellular mechanisms for STDP using whole-cell recording techniques in S1 slices from rats and transgenic mice.

Sensory coding in the whisker system. How sensory information is encoded and processed in the whisker system is little understood, beyond simple coding of whisker identity. We are performing in vivo single unit and whole-cell patch clamp recordings to determine how S1 neurons respond to complex features of whisker stimuli. We are also studying how S1 neurons encode natural stimuli in awake, behaving rats.

    Bender V, Bender K, Brasier DJ, Feldman DE (2006). Two coincidence detectors for spike timing-dependent plasticity in somatosensory cortex. Journal of Neuroscience, 26: 4166-77.

    Bender K, Allen CB, Feldman DE (2006). Synaptic basis for deprivation-induced synaptic weakening in rat somatosensory cortex. Journal of Neuroscience, 26: 4155-65 .

    Gabernet L, Jadhav SP, Feldman DE, Carandini M, Scanziani M (2005). Somatosensory integration controlled by dynamic thalamocortical feed-forward inhibition. Neuron 48: 1-13.

    Feldman DE, Brecht M (2005). Map plasticity in somatosensory cortex. Science 310: 810-5.

    Celikel T, Szostak VA, Feldman DE (2004). Modulation of spike timing by sensory deprivation during induction of cortical map plasticity. Nat. Neurosci. 7: 534-541.

    Allen CB, Celikel T, Feldman DE (2003). Long-term depression induced by sensory deprivation during cortical map plasticity in vivo. Nat. Neurosci. 6: 291-299.

    Feldman DE (2000). Timing-based LTP and LTD at vertical inputs to layer II/III pyramidal cells in rat barrel cortex. Neuron 27: 45-56.

Dan Feldman received his Ph.D. in Neurobiology from Stanford University. He conducted postdoctoral research at the University of California, San Francisco, and the National Institute of Neurological Disorders and Stroke (NINDS). He started his laboratory at UCSD in 2000, and currently holds the Walter F. Heiligenberg Professorship in Neuroethology.