Single unit activity in lateral geniculate body and optic tract of unrestrained cats

In two recent studies of the cat's striate cortex (Hubel, 1959; Hubel & Wiesel, 1959) single units were shown to react to light stimuli in a highly specific manner. Most units responded either feebly or not at all to stimulation of the retina with diffuse light, but gave brisk responses to stationary or moving restricted spots of light. Responses to moving spots often varied with the direction of movement. It was clear that such responses must be the result of complex integrative mechanisms. The present study was undertaken to find out whether similar responses occur in retinal ganglion cells or cells of the dorsal lateral geniculate body. Lateral geniculate units have not previously been studied with restricted light stimulation, and although the cat's retinal ganglion cell has been extensively investigated by Kuffler and his co-workers (Kuffler, 1953; iKuffler, FitzHugh & Barlow, 1957), responses to moving spots were not examined. Thus it has not been possible to say whether the complex activity of cortical units originates in the cortex itself, or at lower levels. Methods for stereotaxic depth recordings in the unanaesthetized unrestrained animal were developed in order to make cortical and depth studies under similar conditions. These techniques make it possible to record from single units from virtually any part of the brain of the freely moving animal.