Hypothalamic influences on the activity of superior colliculus neurons in cats

Experimens on immobilized unanesthetized cats showed that hypothalamic stimulation effectively modifies background and evoked activity of superior colliculus neurons. Some differences in the nature of influences from different hypothalamic areas were revealed. Stimulation of the AHA and HL often caused depression of the background impulsation with initial inhibition, especially during stimulation of HL. Cyclic modulation of background activity was also revealed. The influence of these structures on the activity evoked by light was mostly of modulating character. Stimulation of the ventromedial nucleus produced both inhibitory and excitatory effects on the activity of tectal neurons with a tendency to an increased rate of the latter when using repetitive stimulation.