Superior colliculus cells respond to noxious stimuli.

Neuronal recordings were made in all laminae of the hamster superior colliculus. Specialized cells were encountered in the intermediate and deeper layers which were preferentially, or only, activated by noxious stimuli. Responses to noxious stimuli were blocked by the analgesic drug, etorphine and were reinstated after administering the narcotic antagonist, naloxone. However, these drugs had no obvious effects upon responses to innocuous stimuli. These findings offer direct physiological evidence for the involvement of superior colliculus cells in pain.