Biofeedback

Biofeedback is a method for teaching people how to control various physiological functions in their own bodies. The individual wears various physiological sensors that pick up electrical signals generated by various parts of the body or other kinds of body activity that can be assessed by other kinds of sensors—for example, stretch sensors to assess breathing, pressure sensors to assess tightness of sphincters, or thermal sensors to assess temperature in various parts of the body. The measures are usually shown on a computer screen, although sometimes the physiological information is conveyed through auditory or simple visual stimuli (light bars, etc.), without the use of a computer.

Although some measurement technologies are highly complicated and require considerable training to perform, some are quite simple. For example, a simple indoor-outdoor thermometer with a fast time constant can be used to measure finger temperature, and many electrical sensors are available for a very low cost that assess sweating from the fingers, which is often used as a measure of stress. Individuals then can use the information generated from these sensors to control their own bodies. By looking at a screen and seeing how their temperature is fluctuating, they can gradually acquire the skill to change the temperature in various parts of the body, for example, the fingers. They also can learn to control muscle tension, brain waves (electroencephalographic, or EEG, activity), heart rate variability, blood levels of carbon dioxide, and a variety of other physiological functions.

The first applications of biofeedback began in the 1950s, when investigators found that people were able to exert voluntary control over functions that previously seemed beyond the reach of voluntary control. The first of these studies, by Ralph Hefferline at Columbia University, investigated very small muscle twitches, so small that the individuals did not know when they occurred. Using biofeedback, people learned to both increase and decrease the occurrence of these muscle twitches.

The first studies of vegetative activity, controlled by the autonomic nervous system, were done on sweating from the palms, measured by skin conductance. A small current was passed through the hand (so small that the person could not feel it), allowing assessment of the resistance or its opposite, conductance, of the skin. These studies, by David Shapiro and his colleagues at Harvard University and by H. Kimmel and his colleagues in Florida, found that people were able to both increase and decrease skin conductance or electrical potentials from the palmar skin. This work was soon extended to demonstrating control over heart rate, blood pressure, and finger temperature. One of the first questions that arose at the time was whether people “really” exerted direct control over these functions or whether they achieved these results through control of muscle tension, which indirectly produced effects on other measures. This possibility was quickly eliminated. Scientists found that changes in heart rate and other functions were not correlated with changes in muscle tension. Also, a few very brave individuals volunteered to have the drug curare administered to them. This drug eliminates all muscle tension and, in fact, makes the individual totally paralyzed and helpless. Indeed, artificial ventilation is needed, through a respirator, to keep the individual alive. Even under the influence of curare, people were able to control their skin conductance, hand temperature, and heart rates within certain limits.

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