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Brain Res. 1980 Aug 4;194(2):517-20.

A re-evaluation of the mechanisms underlying simple cell orientation selectivity.


Following from evidence supporting GABA as a putative inhibitory transmitter in the visual cortex, we have iontophoretically applied the GABA antagonist N-methyl bicuculline (Nmb) to simple cells in order to block the inhibitory inputs acting on them. We found that under these conditions previously sharply-tuned simple cells responded equally to all orientations. Moreover receptive field dimensions, judged by the response to stimuli at the optimal and orthogonal orientations, equated best with that expected from a single dLGN cell input. It seems thus, that asymmetries in the excitatory input are not a significant factor in the generation of simple cell orientation selectivity. The asymmetry underlying orientation selectivity rather originates from the operation of an intracortical inhibitory mechanism.

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