Pain responsivity in major depression and bipolar disorder.

Signal detection theory measures of thermal pain responsivity were examined in patients with major depression and bipolar disorder and in control subjects. Patients with major depression had significantly poorer sensory discrimination of painful thermal stimuli than control subjects, but they did not differ from the control subjects in their sensory discrimination of warm thermal stimuli of lower intensity. Patients with bipolar disorder did not differ significantly in sensory discrimination from either the patients with major depression or the control subjects. Patients with major depression had significantly higher (i.e., more stoical) response criteria than the control subjects for the painful thermal stimuli and also for the lower intensity stimuli; patients with bipolar disorder had significantly higher criteria than control subjects for only the lower intensity stimuli. The results suggest that reduced responsivity to pain in major depression may reflect sensory as well as affective abnormalities. Complaints of pain are very common in mood disorders, and continued examination of experimental pain in individuals with these disorders has the potential to enhance our understanding of this phenomenon.