This revised proposal outlines studies designed to assess the capacity of patients with temporomandibular disorders (TMD) to process nociceptive stimuli. The hypothesis that guides this work is that central nervous system inhibitory mechanisms are deficient in TMD patients compared to cohort controls and that this, in turn, results in the abnormal CNS processing of nociceptive sensory information. The proposed studies are designed to identify and characterize maladaptive pain inhibitory mechanisms in TMD patients. Two systems that exert central neural inhibitory effects will be evaluated: 1) the endogenous opioid system and 2) the carotid sinus baroreceptor system. Objective psychophysiological procedures will be used to measure and compare the thermal pain tolerance values, thermal pain discrimination, and time-intensity profiles to cutaneous thermal pain of TMD patients and control subjects. It is hypothesized that endogenous pain regulatory systems are impaired in TMD patients and that this results in an alteration in the perceptual responses to noxious cutaneous stimuli. The outcomes of these studies should provide a better understanding of the perceptual consequences of systematic variations in the activity of central nervous system pain modulatory systems and may provide new insight into the pathophysiology of TMD.