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NJIT Mathematical Biology Seminar

Tuesday, September 16, 2008, 4:00pm
Cullimore Hall 611
New Jersey Institute of Technology

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Is Multiplication Required for Gain Modulation?

Frances Chance

University of California - Irvine

Gain modulation of neuronal responses is widely observed in the cerebral cortex of both anesthetized and behaving animals. This study examines whether multiplicative effects on neuronal tuning curves require underlying multiplicative mechanisms of integration. We compare the effects of a divisive mechanism of inhibition (noisy excitatory and inhibitory synaptic inputs) with two subtractive mechanisms of inhibition (shunting conductance and hyperpolarizing current) on the tuning curves of a model cortical neuron. We find that while the effects of subtractive inhibition can appear nonlinear, they are best described as a vertical shift along the response-axis and are accompanied by a change in response threshold. With a divisive mechanism of inhibition, responses are divisively scaled, reproducing a response-gain control effect. When mutual inhibition between subpopulations of local neurons is included, the model exhibits gain modulation effects that better described as contrast-gain control.