Electrodermal activity (EDA)

Electrodermal activity (EDA), also known as electrodermal response or galvanic skin response, refers to temporary changes in the skin's ability to resist electricity. When a person is calm and relaxed, his or her skin's electrical resistance increases. Conversely, when a person is emotionally aroused (excited, stressed, fearful, etc.), his or her skin's electrical resistance decreases. This decrease seems to be linked to sweat gland activity, a function of the sympathetic nervous system, which is associated with the "fight or flight" response in humans. Over the years, measurements of EDA, taken with a galvanometer, have been used in a wide variety of scientific studies involving emotions, cognitive processing, psychological conditioning, and reactions to sensory stimuli.

Background

Several scientists began investigating EDA during the late nineteenth century. One of these scientists was French researcher Romain Vigouroux. In 1879, he was the first to note the influence of psychological factors in EDA in patients experiencing hysterical anesthesia. He also theorized that EDA was connected to changes in the body's blood flow.

French neurologist Charles Féré was another early investigator of the phenomenon. Féré used an exosomatic method to measure skin conductance levels in response to various emotions. His experiment involved passing a small electrical current across the skin and measuring the skin's resistance to it using a galvanometer, a device that measures electrical currents. Féré found that the various external stimuli that influenced a person's emotions could also cause a decrease in the skin's electrical resistance, making it a better conductor of electricity. His findings were published in the transactions of the Société de Biologie in 1888.

A year later, Russian scientist Ivan Tarchanoff used another method, known as the endosomatic method, to measure the skin's potential conductance response. Unlike Féré's experiment, this method did not involve the use of an external current of electricity. Instead, Tarchanoff placed two electrodes on a subject's skin and measured the changes in the electrical potential between the electrodes after the introduction of physical or mental stimuli. In contrast to Vigouroux, Tarchanoff believed that EDA was related to sweat gland activity rather than blood flow.

In the early 1900s, Carl Jung, a famous Swiss psychiatrist, measured EDA during his word-association investigations with American scientist Frederick Peterson. Jung wanted to find an objective way to analyze the emotional responses to certain words. He and Peterson found that stimuli related to intense emotions, such as anticipation or embarrassment, led to higher readings on the galvanometer.

In the years that followed, more scientists continued investigating EDA. C.W. Darrow's research into the subject in 1927 seemed to support Tarchanoff's theory that EDA was related to sweat gland activity. During Darrow's research, he measured sweat secretion and EDA at the same time. Because the skin's conductance response began before sweat appeared, Darrow believed this indicated that sweat gland activity itself rather than perspiration was more closely involved in EDA.

During the 1950s, American researchers Richard S. Lazarus and Robert A. McCleary also conducted a word-association experiment that measured EDA. However, in this experiment, the researchers used electric shocks to condition their subjects to become fearful of specific words. Exposure to these words produced an increased response on the galvanometer, even when the subject did not receive a shock.

Overview

Researchers continue to investigate EDA into the twenty-first century. One of the reasons that many scientists take measurements of EDA in experiments is because increases in skin conductance levels are considered responses of the sympathetic nervous system, a subdivision of the autonomic nervous system that induces almost immediate motor action. Such responses to intense psychological stimuli are clear signs of sympathetic activity, whereas measurements of other autonomic nervous system responses (such as changes in pupil diameter or blood pressure) may be sympathetic or parasympathetic, meaning the response may be due to other slow-changing processes in the body. Another advantage to using EDA measurements in an experiment is that recording the data is easy and noninvasive. Researchers may also prefer to measure EDA because it is a relatively inexpensive way to collect data on sympathetic nervous system responses when one considers the cost of magnetic resonance imaging (MRI) or positron emission tomography (PET) scans.

Still, there are some disadvantages to measuring EDA in experiments. One disadvantage is that a skin conductance response can be caused by a variety of stimuli. It is not limited to a certain type of situation or event; therefore, researchers must account for numerous variables.

Another possible disadvantage is that each subject is an individual whose physiological and psychological makeup will differ from every other subject tested during the experiment. For example, some subjects may present high rates of nonspecific skin conductance response (NS-SCR), meaning that the response occurs without the presence of an identifiable stimuli. This trait is referred to as electrodermal lability, and people who exhibit it are called labiles. Alternatively, individuals who display low rates of NS-SCR are known as stabiles. Scientists would need to account for the differences between labiles and stabiles in any experiment. This can be done by computing each individual's range of EDA, but it would likely require additional time and effort on the part of the subjects and the researchers.

Over the years, researchers have used EDA for a variety of purposes. It has been used as a type of lie detector by measuring electrodermal spikes in guilty individuals. EDA has also been used in biofeedback conditioning. There is even hope that measuring EDA could assist in the detection of seizures. In some studies, large spikes in EDA have corresponded to individuals experiencing seizures soon afterward. Some companies have already created devices similar to smartwatches that track changes in skin conductance to try to detect unexpected and possibly deadly seizures. Collecting data regarding changes in at-risk individuals' EDA during their daily activities could provide researchers with information that could help them develop new ways to treat epilepsy and other seizure disorders.

Bibliography

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