Biofeedback:

A medical technique used especially for stress-related conditions, such as asthma, migraines, insomnia, and high blood pressure, biofeedback is a way of monitoring minute metabolic changes in one's own body (for example, temperature changes, heart rate, and muscle tension) with the aid of sensitive machines. By consciously visualizing, relaxing, or imagining while observing light, sound, or metered feedback, the client learns to make subtle adjustments to move toward a more balanced internal state.