Sensory physiology of the cerebral cortex.
Dr. Simons’ laboratory investigates neuronal integration within identified, small networks of cerebral cortical neurons. Studies focus on the component of the rodent somatosensory system that processes tactile information arising from the large facial vibrissae, or whiskers. Each whisker correlates one-to-one with an anatomically defined group of cortical neurons, called a barrel, that represents a morphological correlate of a functional cortical column. Barrels are local circuits that perform an initial transformation of incoming signals from the somatosensory thalamus. Computer-controlled whisker stimuli and single cell recording techniques are used to examine how information is integrated by cortical neurons, with a strong emphasis on processing in thalamocortical circuits and the effects of corticothalamic feedback. In collaboration with Dr. George Carvell, recordings also are obtained from animals trained to perform tactile discriminations using their whiskers.
Neurophysiological findings are incorporated into computer models of sensory cortex that simulate known synaptic connections among cortical neurons and the thalamic cells that are presynaptic to them. The model networks are activated by pre-recorded spike trains from thalamocortical relay cells, and responses of the model neurons are compared quantitatively with those obtained in real barrels. In colloboration with Dr. Bard Ermentrout, simulations are used to understand how the dynamical properties of the local circuit account for the neurons’ receptive fields.
Other studies examine the physiological and behavioral effects of abnormal tactile experiences early in life that are produced by trimming the whiskers during critical developmental stages. Trainees in Dr. Simons’ laboratory have the opportunity to combine neurophysiological and modeling studies of cortical neuronal networks. Experimental techniques include single- and multi-electrode recordings, animal behavioral training, computer-based data analyses, and mathematical simulation.
Simons, D.J., and Carvell, G.E. Thalamocortical response transformation in the rat vibrissa/barrel system. J. Neurophysiol. 61: 311-330, 1989.
Bruno, R.M. and Simons, D.J. Feedforward mechanisms of excitatory and inhibitory cortical receptive fields. J. Neurosci., 22: 10966-10975, 2002.
Pinto, D.J., Hartings, J.A., Brumberg, J.C., and Simons, D.J. Cortical damping: Analysis of thalamocortical response transformations in the rodent barrel cortex. Cerebral Cortex, 13: 33-44, 2003.
Temereanca, S. and Simons, D.J. Functional topography of corticothalamic feedback enhances thalamic spatial response tuning in the somatosensory whisker/barrel system. Neuron, 41:639-651, 2004.
Shoyket, M., Land, P.W., and Simons, D.J. Whisker trimming begun at birth or on postnatal day 12 affects excitatory and inhibitory receptive field properties of layer IV barrel neurons. J. Neurophysiol. 94: 3987-3995, 2005.