The overall objective of the proposed research is to obtain an understanding of the brain stem mechanisms of facial pain in Macaca mulatta. To this end, we have proposed two temporally overlapping programs of experimentation. The first makes use of the acute preparation to provide bulbar structures which are fundamentally involved in trigeminal pain: the somatosensory lateral reticular formation and the dorsolateral zones (lamine I-III) of the trigenimal nucleus caudalis. The second incorporates physiological, lesioning and psychophysical techniques in the awake, unanesthetized monkey to further study the involvement of these structures in facial pain. We anticipate that these structures operate in a regulatory fashion, modulating the centripetal flow of nociceptive information from the periphery.