Excitatory convergence of Y and non-Y channels onto single neurons in the anterior ectosylvian visual area of the cat.

Numerous functional and hodological studies of the anterior ectosylvian visual area (AEV) of the cerebral cortex of the cat suggest that this area plays an important role in processing information about visual motion. In the present study, in cats with selective conduction block of Y fibres in one optic nerve, we have examined the extent of the excitatory convergence of Y (presumed 'motion channel') and non-Y information channels on single neurons in AEV, as well as the contribution of the Y channel to the receptive field properties of AEV neurons. While in normal cats all neurons recorded from AEV were binocular, i.e. could be photically activated via either eye, in cats with selective conduction block of Y fibres in one optic nerve, a significant proportion (about 15%) of AEV cells could be photically activated only via the normal eye. In comparison to those in normal cats, the peak discharge rates of AEV neurons in the Y-blocked cats were drastically reduced not only when photic stimuli were presented via the Y-blocked eye, but also when they were presented via the normal eye. Selective block of Y input also resulted in a significant shift in velocity preferences towards the lower velocities. However, the direction selectivity indices of AEV neurons were not affected by selective Y block. Thus: (i) the responses of AEV neurons to a high velocity of motion are dependent on the integrity of the Y input; (ii) the 'spontaneous' (i.e. not photically evoked) discharges of Y retinal ganglion cells exert a facilitatory influence on the responses of AEV cells to photic stimuli; (iii) although the responses of AEV neurons are dominated by the Y inputs, AEV neurons also receive significant non-Y excitatory inputs; and (iv) the strong direction selectivity revealed in most AEV neurons does not dependent on the integrity of Y input.