Until the early 1960s, psychologists believed that animals could not learn complex tasks. Then came pioneering behaviorist B. F. Skinner, Ph.D., who devised a simple system of rewards and punishments that he called operant conditioning. He used operant conditioning to teach pigeons to peck a button only when certain combinations of lights flashed. He also trained mice to build towers out of plastic blocks.

Dr. Skinner thought operant conditioning might also help with toilet training children and performing other human tasks. But Neal Miller, Ph.D., then head of the Laboratory of Physiological Psychology at Rockefeller University in New York City, believed the technique had more profound implications.

Dr. Miller was fascinated by reports that Indian yoga masters and Japanese Zen masters could voluntarily control pulse, blood pressure, and metabolic rate-bodily functions that physiologists had long considered completely involuntary. He speculated that the yogis and Zen masters might be using a form of internal operant conditioning to alter their physiology.

In a classic series of experiments, Dr. Miller used a Skinnerian system of rewards and punishments to teach rats to raise and lower their heart rates, blood pressures, ear temperatures, kidney functions, and intestinal muscle contractions. When his research was published in a 1969 issue of Science, the nation's top research journal, it forever changed how Western scientists viewed learning. They realized that "involuntary" biological processes could be voluntarily modified with the right rewards, or feedback-hence the name biofeedback.

Your Mind Speaks, Your Body Listens

By the late 1970s, biofeedback had become an industry. Manufacturers developed simple, inexpensive biofeedback devices to monitor breathing, pulse rate, temperature, muscle tension, or minute changes in perspiration. By regulating these bodily functions, the theory goes, people can make their bodies relax. And that enables them not only to manage stress but also to treat specific medical conditions.

"Biofeedback is not a cure-all," says Francine Butler, Ph.D., executive director of the Association for Applied Psychophysiology and Biofeedback in Wheat Ridge, Colorado. "But it helps treat stress-related health problems." Among those problems are tension headaches, migraines, asthma, and incontinence. There's also evidence that biofeedback can help with temporomandibular disorder (TMD) and congestive heart failure.

TMD is a condition characterized by chronic pain around the temporomandibular joint, which connects the jaw to the skull. It has several possible causes, including chronic tension in the jaw muscles. Studies by Leonard Hukzinski, Ph.D., director of biofeedback services in the department of psychiatry at the Ochsner Medical Foundation in New Orleans, have shown that biofeedback provides effective long?term relief from tension-related TMD.

This therapy may also help people who have congestive heart failure. Researchers gave biofeedback training to 20 people with congestive heart failure, theorizing that biofeedback could improve circulatory efficiency. And they were right: The patients showed significant increases in the diameter of their blood vessels, which enhanced circulation and boosted their hearts' blood output.

One Therapy, Many Forms

Today, several thousand certified biofeedback therapists teach the" necessary skills to tens of thousands of people every year. Thousands more people learn biofeedback on their own, using small home devices and the instruction books that come with them. (Home biofeedback equipment is available in some department stores and through some health-oriented mail-order catalogs.)

Just how does a biofeedback machine work? Well, suppose that you're feeling tense. Anxiety causes the tiny blood vessels in your hands to constrict, and, in turn, the skin temperature of your hands drops a few degrees. The biofeedback machine has a temperature-sensitive pad that's attached to a thermometer. When you touch the pad, the thermometer displays your skin temperature and, depending on the model, emits a high-pitched tone. Then as you relax, the number on the thermometer goes higher, while the tone goes lower.

Biofeedback neophytes often have trouble adjusting their skin temperatures. But with a little coaching, they learn to breathe deeply and to notice small but important changes in the thermometer reading and tone. Pretty soon, they can warm their hands at will-and as they do, they feel more relaxed.

Not all biofeedback machines monitor skin temperature. As mentioned earlier, various models can track an assortment of bodily functions, including temperature, pulse, breathing, muscle tension, and brain waves. One type of biofeedback even tests the electrical conductivity of the skin, or galvanic skin response (GSR). This type of biofeedback is used to treat anxiety, insomnia, obesity, and chemical dependencies like drug addiction. It's also helpful for controlling overactive sweat glands (a condition called hyperhydrosis). Home biofeedback devices typically measure GSR.