Influence of the visual cortex on responses of retinal ganglion cells in the rat.

The objective of the present investigation was to answer the following question: Does the visual cortex affect the neuronal firing of retinal ganglion cells in the rat? To test this hypothesis, the visual cortex was inactivated by a reversible cryoblockade. Action potentials of a ganglion cell were recorded from its axon at the optic tract level prior to, during, and following cortical blockade. The results indicated that indeed the visual cortex influenced the retinal output since its inactivation led to a modification of the firing pattern evoked in response to a flash of light. In most cases the modification was an increase of the bursting pattern of the evoked discharges. By contrast cooling nonvisual areas failed to modify ganglion cells' discharge. A comparison between cortico-geniculate and cortico-retinal feedback loops seems to suggest that the first path is involved mostly with the spatial organization of center-surround receptive fields, whereas the second path is associated with temporal aspects of the retinal responses in the rat.