Subcortical mechanisms in orientation sensitivity of cat visual cortical cells.

The orientation biases seen in the responses of neurones of the dorsal lateral geniculate nucleus (dLGN) can be reduced by the local application of the GABA antagonist, bicuculline methiodide. This fact was exploited to investigate whether these biases are important for cortical orientation selectivity by measuring the orientation sensitivity of cortical cells before and during iontophoretic administration of bicuculline in the topographically corresponding region of the dLGN. This procedure led to a significant reduction in the orientation sensitivity of the cortical cell. The results suggest that subcortical orientation biases are at least partly responsible for the orientation sensitivity seen at the level of the striate cortex.