Centrifugal and centripetal connections of the cat visual cortex

In experiments on curarized cats unit responses in the dorsal lateral geniculate body to stimulation of various zones in area 17 of the visual cortex were analyzed. Of all cells tested 69% were found to respond antidromically and 8% orthodromically; in 7.6% of cells IPSPs occurred either after an initial antidromic spike or without it. The velocities of conduction of excitation along the corticopetal fibers of the optic radiation varied from 28 to 4.3 m/sec, but the three commonest groups of fibers had conduction velocities of 28-19, 14-12, and 10-9.5 m/sec. A difference between latent periods of antidromic responses of the same neurons was found to stimulation of different zones of the visual cortex; this indicates that axons of geniculo-cortical fibers split into several branches which form contacts with several neurons in area 17 of the visual cortex. The degree and possible mechanisms of cortical influences on neurons of the lateral geniculate body are discussed.