Mathematical Biology Seminar Frances Chance UC Irvine Wednesday Dec. 8, 2009 3:05pm in LCB 225 Is Multiplication Required for Cortical Gain Modulation? Abstract: Gain modulation of neuronal responses is widely observed cortical phenomenon that is often described as a multiplicative scaling of neuronal responses. We examine whether multiplicative mechanisms of input integration, as might be measured in vivo, are required for multiplicative effects on neuronal tuning curves. We compare the effects of a divisive mechanism of inhibition with two subtractive mechanisms of inhibition 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 are better described as input-gain control.