Skin conductance

Electrodermal activity (EDA), is the property of the human body that causes continuous variation in the electrical characteristics of the skin. Historically, EDA has also been known as skin conductance, galvanic skin response (GSR), electrodermal response (EDR), psychogalvanic reflex (PGR), skin conductance response (SCR), sympathetic skin response (SSR) and skin conductance level (SCL). The long history of research into the active and passive electrical properties of the skin by a variety of disciplines has resulted in an excess of names, now standardized to electrodermal activity (EDA).

The traditional theory of EDA holds that skin resistance varies with the state of sweat glands in the skin. Sweating is controlled by the sympathetic nervous system, and skin conductance is an indication of psychological or physiological arousal. If the sympathetic branch of the autonomic nervous system is highly aroused, then sweat gland activity also increases, which in turn increases skin conductance. In this way, skin conductance can be a measure of emotional and sympathetic responses. More recent research and additional phenomena (resistance, potential, impedance, and admittance, sometimes responsive and sometimes apparently spontaneous) suggest that EDA is more complex than it seems, and research continues into the source and significance of EDA.

The study of EDA has led to such important and vital tools as the electrocardiograph (ECG or EKG) and the electroencephalograph (EEG).

In 1849, Dubois-Reymond in Germany first observed that human skin was electrically active. He immersed the limbs of his subjects in a zinc sulfate solution and found that electric current flowed between a limb with muscles contracted and one that was relaxed. He therefore attributed his EDA observations to muscular phenomena. Thirty years later, in 1878 in Switzerland, Hermann and Luchsinger demonstrated a connection between EDA and sweat glands. Hermann later demonstrated that the electrical effect was strongest in the palms of the hands, suggesting that sweat was an important factor.

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