Tuning of striate neurons to cross-shaped figures in conditions of local blockade of intracortical inhibition.

The recently observed selective sensitivity to cross-shaped and angular figures was studied in 85 primary visual cortex (field 17) neurons in cats before and after local blockade of GABA(A)ergic inhibition by microiontophoretic application of the GABA antagonist bicuculline. Two opposite effects were seen: half of the neurons studied showed decreases or complete loss of sensitivity to crosses, and a third of the cells showed increases or the appearance of sensitivity to crosses. These data provide evidence for significant roles for intracortical inhibition in providing sensitivity to crosses and intersecting lines in two types of visual cortex neurons, the effects on these two types of neuron being opposite.