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Electrodermal activity ( EDA) is the property of the human body that causes continuous variation in the electrical characteristics of the Human 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 in the skin. Sweating is controlled by the sympathetic nervous system, (2025). 9780130615671, Benjamin Cummings. ISBN 9780130615671 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 glands activity also increases, which in turn increases skin conductivity. In this way, skin conductivity can be a measure of emotional and sympathetic responses. But the theory associating sweat and EDA was already debated decades ago since individuals without sweat glands have an EDA signal : "" The source of the skin potential is presumed to be the sweat glands and the epidermis, although it is present in subjects with congenital absence of sweat glands ... this is not a test of “sweat” function, it is often included in this category as a measure of sudomotor activity".". This debate is ongoing since more recent technology (see Electrochemical skin conductance) demonstrated a real measure of sweat conductivity with several medical applications. A good way to differentiate both is to look at measures values and type :
More research is needed and inclusion of additional phenomena (resistance, potential, impedance, Electrochemical skin conductance, and admittance, sometimes responsive and sometimes apparently spontaneous) suggest that EDA is more complex than it seems. There is a knowledge limitation, as wearable brands have included an EDA measure as a feature : " This aspect leads to the conclusion that the reliability of consumer wearables must be further investigated, especially by combining raw data collection with specific preprocessing techniques".
Vigouroux (France, 1879), working with emotionally distressed patients, was the first researcher to relate EDA to psychological activity. In 1888, the French neurologist Féré demonstrated that skin resistance activity could be changed by emotional stimulation and that activity could be inhibited by drugs.
In 1889 in Russia, Ivane Tarkhnishvili observed variations in skin electrical potentials in the absence of any external stimuli, and he developed a meter to observe the variations as they happened in real time.Handbook of Clinical and Experimental Neuropsychology (eds. Gianfranco Denes, Luigi Pizzamiglio). Psychology Press, 1999. . Page 33.
The scientific study of EDA began in the early 1900s. One of the first references to the use of EDA instruments in psychoanalysis is the book by C. G. Jung entitled Studies in Word Analysis, published in 1906. The Biofeedback Monitor Jung and his colleagues used the meter to evaluate the emotional sensitivities of patients to lists of words during word association. Jung was so impressed with EDA monitoring, he allegedly cried, "Aha, a looking glass into the unconscious!" Jung described his use of the device in counseling in his book, Studies in Word Association, and such use has continued with various practitioners.
The controversial Austrian psychoanalyst Wilhelm Reich also studied EDA in his experiments at the Psychological Institute at the University of Oslo, in 1935 and 1936, to confirm the existence of a bio-electrical charge behind his concept of vegetative, pleasurable "streamings".Reich, W. "Experimentelle Ergebnisse ueber die electrische Funktion von Sexualitat und Angst" (Sexpolverlag, Copenhagen, 1937). Translated as "Experimental investigation of the electrical function of sexuality and anxiety" in Journal of Orgonomy, Vol. 3, No. 1-2, 1969.
By 1972, more than 1500 articles on electrodermal activity had been published in professional publications, and today EDA is regarded as the most popular method for investigating human psychophysiological phenomena. As of 2013, EDA monitoring was still on the increase in clinical applications.
Human extremities, including fingers, palms, and soles of feet display different bio-electrical phenomena. They can be detected with an EDA meter, a device that displays the change in electrical conductance between two points over time. The two current paths are along the surface of the skin and through the body. Active measuring involves sending a small amount of current through the body.
Some studies include the human skin's response to alternating current, including recently deceased bodies.
The combined changes between electrodermal resistance and electrodermal potential make up electrodermal activity. Galvanic skin resistance (GSR) is an older term that refers to the recorded electrical resistance between two electrodes when a very weak current is steadily passed between them. The electrodes are normally placed about an inch apart, and the resistance recorded varies according to the emotional state of the subject. Galvanic skin potential (GSP) refers to the voltage measured between two electrodes without any externally applied current. It is measured by connecting the electrodes to a voltage amplifier. This voltage also varies with the emotional state of the subject.
EDA is highly responsive to emotions in some people. Fear, anger, startled response, orienting response, and sexual feelings are among the reactions that may be reflected in EDA. These responses are utilized as part of the polygraph or lie detector test.
EDA in regular subjects differs according to feelings of being treated fairly or unfairly, but psychopaths have been shown to manifest no such differences.Oshumi, T., Ohira, H. "The positive side of psychopathy: Emotional detachment in psychopathy and rational decision-making in the ultimatum game". Personality and Individual Differences 49, 2010, pp. 451-456 This indicates that the EDA record of a polygraph may be deceptive in a criminal investigation.
Phasic changes (EDR) are short-lasting changes in EDA that appear as a response to a distinct stimulus. EDRs can also appear spontaneously without an observable external stimulus. These types of EDRs are referred to as "nonspecific EDR" (NS.EDR). The phasic EDR is useful when investigating multifaceted attentional processes. (2025). 9780511279072, Cambridge University Press. ISBN 9780511279072
Tonic changes (EDL) are based on the phasic parameters. The spontaneous fluctuations of nonspecific EDR can be used to evaluate tonic EDA. More specifically by using the frequency of "nonspecific EDR" as an index of EDA during a specific time period, e. g. 30–60 seconds. Tonic EDA is considered useful in investigations of general arousal and alertness.
EDA has also been studied as a method of pain assessment in premature born infants.
Often, EDA monitoring is combined with the recording of heart rate, respiratory rate, and blood pressure, because they are all autonomically dependent variables. EDA measurement is one component of modern polygraph devices, which are often used as lie detectors.
The E-meter used by the Church of Scientology as part of its practice of "auditing" and "security checking", is a custom EDA measurement device.
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