Biofeedback is a method of learning to control body processes that are not ordinarily thought of as being under voluntary control. People have learned to regulate their blood flow, blood pressure, body temperature, brain waves, heartbeat, and other internal body functions. Normally, the autonomic (self-regulating) part of the nervous system controls such processes automatically. People can also use biofeedback to relearn to use muscles no longer under their voluntary control because of an accident, stroke, or brain damage.