Effects of eye movements upon excitability of cat superior colliculus as tested by electrical stimulation of the cortico-collicular pathway.

Influences of saccadic eye movements upon excitability of superior colliculus (SC) were examined in chronic cats carrying implanted electrodes and in encéphale isolé cats. Excitability of SC was assessed by recording responses of SC to electrical stimulation of cortico-collicular (CC) pathway. The SC response to stimulation of CC fibers consisted of two componenets, i.e. presynaptic T and postsynaptic R. Eye movements enhanced R but did little change T. Enhancement of the postsynaptic component R was ascribable to a central factor on the basis of the following results: 1) Enhancement of R occurred independently of whether the ambient illumination was present or not. 2) Saccade-like movements of a slit of light in front of immobilized eyes never induced enhancement of R. 3) PRF stimulation, effective to cause saccade-like eye movements, always elicited enhancement of R, independent of the ambient condition of eyes and even after eyes had been immobilized.