Further studies of the neural mechanisms of ketamine-induced anesthesia in the rhesus monkey.

Bipolar stimulation of tooth pulp was used to elicit evoked potentials in the cortex, thalamus, and midbrain reticular formation (MBRF) of 4 monkeys. Averaged evoked potentials in MBRF and medial thalamic nuclei were either completely obliterated or markedly reduced in amplitude by anesthetic dosages of ketamine. In contrast, little effect was observed upon the primary response elicited in the ventrobasal complex of the thalamus. These results suggest that anesthetic doses of ketamine block afferent signals concerned with the affective-emotional components of pain perception, but conduction of signals related to the localization of somatic stimuli in time and space may be relatively unimpaired.