Influences of cortico-tectal and intertectal connections on visual responses in the cat's superior colliculus

Summary Our experiments, utilizing electrical shocks applied to the lateral- or supra-sylvian gyrus of the cortex, demonstrate an initially excitatory (latency 2–10 msec) but predominantly inhibitory influence of cortico-tectal afferents on the discharge of tectal neurons. Primary or secondary inhibition in tectal cells after cortical stimulation suppressed spontaneous or visually driven activity and limited the frequency of stimulation which tectal neurons could follow.The main influence of the contralateral colliculus on visual responses of tectal cells is inhibitory but again some principally monosynaptic intertectal connections evoked initial excitation (latency 3–10 msec) after electrical stimulation of the contralateral optic tract.Removal of the visual areas 17, 18 and 19 did not cause a loss of movement- or direction-selectivity in neurons of the superior colliculus. Cooling of the occipital cortex, while recording from direction-selective tectal neurons did not alter their essential response characteristics. The response to cortical shocks disappeared in tectal neurons during cooling but could be restored by rewarming of the cortex.It could not be confirmed in our experiments that excitation and movement- or direction-selectivity of neurons in the superior colliculus depend on a specific input from areas 17, 18 and 19 of the cortex.