Distinct X- and Y-streams in the cat visual cortex revealed by bicuculline application.

Responses of striate cortical 'simple' cells to photic stimuli were compared with those of X- and Y-geniculate cells as the simple cells' intra-cortical inhibitory inputs were locally blocked by bicuculline. Blockage was confirmed in 21 simple cells by substantial reductions of their orientation and direction selectivities. All but one of them exhibited either X-like (11) or Y-like (9) responses. This suggests that a given simple cell receives only one type of geniculate input.