Orientation selectivity of cortical neurons during intracellular blockade of inhibition.

Neurons in the primary visual cortex of the cat are selectively activated by stimuli with particular orientations. This selectivity can be disrupted by the application of antagonists of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) to a local region of the cortex. In order to determine whether inhibitory inputs are necessary for a single cortical neuron to show orientation selectivity, GABA receptors were blocked intracellularly during whole cell recording. Although the membrane potential, spontaneous activity, subfield antagonism, and directional selectivity of neurons were altered after they were perfused internally with the blocking solution, 18 out of 18 neurons remained selective for stimulus orientation. These results indicate that excitatory inputs are sufficient to generate orientation selectivity.