Intracortical Network Dynamics and Control of Neuronal Gain.
David A. McCormick, Bilal Haider, Alvaro Duque
Dept. Neurobiology, Kavli Institute for Neuroscience, Yale University School of Medicine
The functional connectivity of the neocortex varies moment to moment, based upon the level of responsiveness, or gain, of intervening neurons. We have examined how recurrent network activity, such as that which may underlie top-down influences, may influence neuronal responses. Visual responses in cat primary visual cortex were found to be strongly influenced by the membrane potential, decreasing significantly with even sub-mV hyperpolarizations. To examine how changes in membrane potential may effect input-output relationship of cortical neurons, we examined the response of V1 neurons to visual stimuli of varying contrast and measuring the probability that these stimuli initiated action potentials (contrast response curve). Hyperpolarization of the membrane potential, occurring either spontaneously through withdrawal of recurrent network activity or induced with the intracellular injection of current, resulted in a strong suppression of visual responses. This suppression was expressed as a decrease in “gain” of the contrast response curve. Interestingly, multiple examples of change in neuronal gain, such as those that may underlie top-down influences, exhibit similar changes in neuronal gain. Our results suggest that a simple change in membrane potential, as small as less than 1 mV, may contribute to rapid changes in neuronal gain and network interactions. These results are consistent with the hypothesis that the functional connectivity of the cerebral cortex is constantly updated on a moment to moment basis through rapid changes in membrane potential so as to solve behavioral demands
