According to Katrina Berne, Ph.D., "Biofeedback applications are relevant to a number of CFS/FMS symptoms, including muscle tension, pain, and headache. The basic principle is simple: to provide auditory or visual feedback when a desired physiological change is produced. Brain waves, blood flow, and muscle tension can be measured with electrodes taped to various body points, with sounds or lights offering feedback in regard to muscle tension or other relevant functions. By associating the desired state with positive feedback, the behavior change is learned and reinforced, becoming easier to achieve over time. Ultimately, the patient is able to produce the response without the aid of equipment and apply the techniques in daily life." (Source: Chronic Fatigue Syndrome, Fibromyalgia and Other Invisible Illnesses, by Katrina Berne, Ph.D. Published by Hunter House and available at www.hunterhouse.com or by calling 1-800-266-5592.