Activity of somatic origin evoked in the superior colliculus of the cat

Abstract

Electric stimulation of the four limbs evokes two types of responses in the superior colliculus of the cat: a short latency response and a long latency one. The visual cortex influences the long latency responses recorded from the ipsilateral colliculus. After surgical ablation or pharmacological depression of the visual cortex the long latency collicular responses completely disappear. Enhancement of the long latency responses was obtained by strychninization of the visual cortex. Effects of continuous retinal illumination or ischemic deafferentation resemble those of cortical strychninization and are similarly affected by depression or surgical ablation of the visual cortex. These procedures do not affect the short latency collicular responses. These results suggest that the visual cortex constitutes a relay in the pathway followed by the long latency collicular responses. Unilateral section of the anterolateral funiculus at the thoracic level diminishes the amplitude of both somatic responses recorded from the superior colliculus to the stimulation of any of the hind limbs. After a bilateral section of the ventrolateral funiculi both somatic collicular responses disappear. Electric stimulation of the medial bulbar reticular formation at the region of the nucleus reticularis gigantocellularis elicits short and long latency collicular responses identical to those evoked by peripheral stimulation. These findings suggest that the peripheral impulses which evoke both types of collicular response follow a common pathway up to the bulbar level.