To Your Health

Can galvanic skin response tests be trusted?

Q. Is the galvanic skin response a reliable way to tell which foods are bad for me?

A. The galvanic skin response has gone through many phases of interest over the past 100 years. GSR, also known as the Tarchanoff Phenomenon first described by Jean de Tarchanoff in 1890, is a change in the electrical properties of the skin in response to stress or anxiety. Like so many other observations, GSR has been used for decades with no real understanding of how it works. The reduced resistance of the skin to the passage of a very small electric current was originally thought to be entirely due to an increase in perspiration, but the change is much too rapid for this explanation to be correct. Axons that are part of the autonomic, or "involuntary", nervous system are clearly involved, but so are certain prostaglandins, the chemical messengers used in the inflammatory response.

GSR has been used by law enforcement as a lie detector, by Scientologists in spiritual counseling, by physicians to treat epilepsy, by acupuncturists to locate meridians, and by psychologists for biofeedback conditioning. Some health-care providers have also used it in their efforts to diagnose food allergies and select appropriate treatments. The U.S. Food and Drug Administration and the attorneys general of several states consider the latter use fraudulent and have vigorously prosecuted some health-care providers who use instruments based on GSR in their practices.

The measurement of GSR is amazingly simple. You can pay thousands of dollars for a computerized instrument, but you can also build your own from about $5 worth of parts. It is the interpretation of the results of the measurements that is extremely difficult and controversial. The major problem with the application of GSR readings to human health is that the mind as well as the body has a profound effect on these readings. One of the reasons that GSR is useful as a lie detector is that the mind knows when a statement is a lie and changes the GSR reading. But the readings are also affected by what we remember and even what we imagine while the test is being done. Testing the GSR response to a food reflects not only the immunological response but also the associations of that food to prior experiences.

It appears that GSR is basically a measure of stress, and Dr. Hans Selye demonstrated long ago that stress is a body response, not an event. While GSR measurements may not be appropriate for detection of food allergies or food intolerance, even though these events are stressful, researchers still find many uses for it. For instance, detecting elevated stress in students using a computer-based training system allows adjustments in the pace of the training. Similarly, patients recovering from oral-cancer surgery often experience considerable frustration as they learn again how to talk. GSR is an indication of the level of their dissatisfactions with themselves as they practice their pronunciation of words and a signal for the need to change methods of speech therapy. In other experiments, GSR was used to determine the extent of nerve damage in diabetic patients and to measure the intensity of taste sensations.

With such a large number of reasonable uses for GSR, it seems unproductive to try to apply it in a situation to which it is not well suited.

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