Biofeedback involves non-invasive, simple electronic monitoring to observe the body's functions and provide information useful to the healing processes, especially with stress. Biofeedback instruments record continuous information about subtle changes in physiological stress responses (such as muscle tension, hand temperature, respiration, or heart rate). Using this information, guided relaxation techniques allow awareness, and methods to control the particular body reactions underlying symptoms are learned. Treatments may address anxiety, asthma, chronic pain, menstrual pain, hypertension, insomnia, migraine headaches, muscle spasms, and other stress-related disorders.