Visual receptive fields of cat cortical neurons lack the distinctive geniculate Y cell signature

Retinal ganglion and lateral geniculate cells of the primary visual pathway may be categorized as X or Y according to their spatial linearity summation properties. In particular, Y cell spatial-frequency transfer functions have a distinctive spatial--linearity signature. Their receptive fields comprise a temporally and spatially linear mechanism (center plus antagonistic surround) that responds to relatively low spatial frequency stimuli, and a temporally nonlinear mechanism, coextensive with the linear mechanism, that--though broad in extent--responds best to high spatial-frequency stimuli. This component exhibits spatially nonlinear properties. We looked for this Y cell signature in cat visual cortical cells. If the predominant excitatory input to a certain type of cortical cell were from lateral geniculate nucleus (LGN) Y cells, we would expect to find the Y cell signature underlying the cortical cell transfer function. However, we have not found this Y cell signature in any of the cortical cell studied, and in particular not in the nonlinear complex cells. This would suggest that cortical spatial summation nonlinearities are not functionally derived from input Y cell nonlinearities.