What is biofeedback for mental illness?

Biofeedback is a method that uses the mind to control a body function that the body normally regulates automatically.

Biofeedback is sometimes used as an adjunct treatment for people with mental illness. Biofeedback-assisted relaxation can help people learn to relax. By seeing some aspects of their body on computer screen or hearing a tone that changes in pitch they are able to relax their autonomic nervous system