Some functions in the body occur automatically, outside of conscious control (such as heart rate and blood pressure). Biofeedback is a method of making those “involuntary” processes something you can do at will.

The basic method is quite simple. In biofeedback, a machine gives you direct information regarding the bodily process in question (the “feedback” part of the term “biofeedback”). Given this information, you can find a way to control it, just like you can learn to wiggle your ears if you try hard enough.

For example, your blood pressure might be displayed on a screen. Blood pressure naturally goes up and down from time to time. When it goes down, you’ll notice that and feel pleased; when it goes up, you’ll feel displeased. Pleasure and displeasure act like the reward and punishment technique used for training animals. When a rat in a maze is rewarded with food for going the right way and given an electric shock for going the wrong way, it will soon learn to go the right way. Similarly, the unconscious parts of the nervous system figure out a way to get a "reward" instead of receive "punishment." In the case just described, this means reducing blood pressure.

The display screen provides the feedback because normally we can’t detect our own blood pressure. Using a machine to provide that information allows the person to achieve conscious control. This process generally works, at least to a modest extent. After a number of sessions, most people reach a place where they can lower their blood pressure simply by thinking, “I want my blood pressure to fall.” They don’t know how they're doing it (any more than ear wigglers know how they’ve accomplished that); nonetheless, they can cause the desired effect.

In addition to measuring blood pressure and heart rate, there are biofeedback machines in fairly common use that measure muscle tension, skin temperature, skin resistance to electricity, and brain wave activity.

Probably the most common use of biofeedback is to treat stress and stress-related conditions, including anxiety, insomnia, high blood pressure, fibromyalgia, muscle pain, migraine headaches, and tension headaches.