Influence of a local inactivation in the superior colliculus on lateral geniculate responses in rabbits

The influence of the superficial layers of the superior colliculus (SC) on responses of the lateral geniculate nucleus was studied in anesthetized and paralyzed rabbits. Fifty to one hundred nanoliters of inactivating drugs were injected through a micropipette positioned in the SC in register with the geniculate cells. The latter were tested with discrete moving and stationary targets presented in random sequences. Results revealed that the SC exerted a dual facilitative (n = 19) and inhibitory (n = 25) influence. The latter segment of the response pattern was modified while the initial portion remained unchanged. In some cases differential effects were observed, that is, the responses to one particular stimulus were more affected than responses to other modalities. However, in the majority of cells it was the on-off responses which were most affected. These findings point toward complex influences of the SC upon geniculate responses in rabbits. This complexity is also supported by findings that in cats the colliculo-geniculate synapses are of various types.