Convergence of retinal inputs onto visual cortical cells: II. A study of the cells disynaptically excited from the lateral geniculate body.

Spike discharges were recorded extracellularly from cells located in the superficial layer of cat's visual cortex. These cells were disynaptically excited and trisynaptically inhibited from the lateral geniculate cells. The vast majority of them responded to stationary and moving light stimuli. Their ON and OFF responses to a flash of light slit consisted of three components: (1) initial excitation, (2) depression and (3) later rebound. The three components were evoked from a broad area of the retinal receptive field. In one group of these cells, exploration of the receptive field with light slits of different lengths revealed a strong depressant zone at one or both ends of the excitatory receptive area, the characteristics property of 'hypercomplex' cell of Hubel and Wiesel. Another population of cells, however, did not show such length-specificity, and apparently correspond to 'complex' cell. In both groups of cells electrical stimulation at the excitatory receptive area produced a sequence of excitation, depression and later rebound, but only depression was evoked from the depressant zones. The latency of the excitation (6 msec) and the depression (7 msec) are in accordance with the view that the excitation is transmitted through disynaptic pathway and the depression through trisynaptic pathway after being mediated by the lateral geniculate cells.