“Synaptic Input to Single Cortical Neurons in Rodents and the Behaving Primate” 

Andrew Tan, Ph.D.*
Postdoctoral Fellow
Center for Perceptual Systems
Department of Neuroscience
The University of Texas at Austin

Seminar will be made available via videoconference in the Health Sciences Research Building, room E 182 and Technology Enterprise Park, room 104.

The cerebral cortex enables mammals to recognize objects.  As the cortex is a network of excitatory and inhibitory neurons, cortical activity is created by the interaction of excitation and inhibition.  I will present in vivo whole cell measurements showing different patterns of net synaptic excitation and net synaptic inhibition that single cortical neurons in anesthetized rodents can receive, depending on whether the cortex is spontaneously active or responding to a sensory stimulus.  In behaving animals, the cortical network of excitatory and inhibitory neurons has been hypothesized to be in an asynchronous high conductance state in which a neuron’s membrane potential hovers below spike threshold, and its net synaptic input is nearly Gaussian, arising from many uncorrelated inputs.  To test this hypothesis, we developed a technique to perform whole-cell membrane potential measurements from the cortex of behaving monkeys, focusing on primary visual cortex of monkeys performing a visual fixation task.  Our data indicate that, contrary to the predictions of an asynchronous state, membrane potential during fixation was far from threshold, and distributions of membrane potential fluctuations were skewed beyond that expected for a range of Gaussian input.  Furthermore, spontaneous fluctuations in membrane potential were correlated with the surrounding network activity.  Visual stimulation, however, led to responses more consistent with an asynchronous state: membrane potential approached threshold, fluctuations became more Gaussian, and correlations between single neurons and the surrounding network were disrupted.  These observations show that sensory drive can shift cortical circuitry from a synchronous to an asynchronous state.

Faculty Host: Garrett Stanley, Ph.D.