抄録
In many cells of the primary visual cortex (V1), stimuli in the receptive field surround suppress the responses to stimuli presented in the classical receptive field. We have studied surround suppression in membrane potential and conductance changes of simple cells in anesthetized cats. Like surround suppression in spike responses, suppression in membrane potential was selective for surround orientation. Suppression was amplified by spike threshold, being stronger for firing rate than for membrane potential. Surprisingly, surround stimulation reduced both the excitation and inhibition received by a cell. This reduction is not caused by a reduction of the input from geniculate relay cells: Suppression in relay cells was not orientation selective. These results suggest that V1 operates as an inhibition-stabilized network, in which recurrent excitation is by itself unstable, but is stabilized by feedback inhibition. We assume that surround stimuli activate excitatory input onto inhibitory cells. The sequence of events when a surround stimulus is added to a center stimulus is as follows. The activity of inhibitory cells is transiently increased. The activity of excitatory cells is decreased by the increase in inhibition. The activity of excitatory cells is further decreased by the reduction of recurrent excitation. The activity of inhibitory cells is also decreased by the reduction of total excitation in the network. As a result, both the excitation and inhibition onto cells are reduced. [J Physiol Sci. 2007;57 Suppl:S38]
