A feedback dermograph measures the electrical conductance or electrical potential in the individual's skin. The galvanic skin response (GSR) biofeedback machine can monitor minute changes in the concentration of salt and water in sweat gland ducts. The natural metabolism of cells produces a slight voltage
Biofeedback that varies as sweat gland activity changes. The lower the measurable voltage, in millivolts, the less there is of sweat gland activity. With skin conductance techniques an imperceptible electric current is passed through the skin. As the sweat glands become more active, the monitor registers the skin's increased ability to conduct electricity. The reverse of this procedure is called skin resistance.
The GSR has been used in lie detectors as a measure of emotional arousal. The sympathetic branch of the autonomic nervous system controls sweating. GSR biofeedback helps the individual gain control of the arousal produced by the autonomic nervous system. Two sensors or electrodes are usually placed on the ends of two fingers. Many clinicians prefer not to use GSR responses because they change rapidly and often respond to irrelevant stimuli.
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