Inhibitory and excitatory binocular convergence to visual cortical neurons of the cat.

Responses of 182 visual cortical (VC) neurons to electrical stimulation of both optic nerves (ON) were recorded intra- and extracellularly, and their eye dominance determined with visual stimuli. Many VC neurons could not be excited by ON stimulation without simultaneous activation by visual stimulation of the eye of the other side. The ON-excited units (25 simple and 71 complex cells) had essentially the same response latency from both ONs. In almost all VC neurons including those not driven from the ON, ON stimulation elicited inhibition which was shown to be post-synaptic in all neurons recorded intra- or quasi-intracellularly. The onset latency of IPSPs not preceded by an action potential or EPSP was 4.2+/-1.0 msec, suggesting that intracortical inhibition was initiated by afferent impulses mediated through fast conducting fibers. In visually monocular neurons, ON stimulation of the non-driving side also elicited primary inhibition. Visually binocular, but monocular-dominant neurons responded more reliably to ON stimulation of the dominant side than to the other. In most binocular neurons with equal visual responsiveness to both eyes, inhibition and excitation evoked from both ONs had about the same latency and magnitude.