No matter how great your poker face might be, your skin can’t keep a secret. A window into the human mind through physiology exists beyond crystal balls, witches, or horrific psychological control. The very electricity that we associate with changing brain activity in horror movies can serve as a hidden gateway into your mind.
Electrodermal activity (EDA) recordings, particularly of palmar and plantar skin, are one of the original methods of recording psychophysiological responses, like stress, having been used as an evaluative tool in psychophysiological research since the late 19th century (Boucsein et al. 2012). Today, EDA is a useful, noninvasive, and low-cost way of studying emotional and sympathetic responses during cognitive or emotional stimulation (Banganho et al. 2022; Rahma et al. 2022). EDA serves as a valuable diagnostic tool utilized in research on stress, anxiety, and even neurological conditions like epilepsy (Banganho et al. 2022).
Underlying these applications is a physiological link between the sympathetic nervous system (SNS) and the integumentary system, through the skin (Greco et al. 2016). EDA is controlled by the SNS, or fight-or-flight response, which exhibits particular bodily responses, like stress, upon detection of a threat-like stimulus. Eccrine glands, or sweat glands, are supplied by nonmyelinated class C fibers, which are regulated by the hypothalamus, alongside components of the limbic and reticular system. The SNS innervates eccrine glands through cholinergic fibers and adrenergic fibers. Cholinergic fibers are key in the body’s thermoregulation, causing varying discharge of sweat with changes in temperature. On the other hand, adrenergic fibers present on the soles and palms activate during emotional stress, allowing them to be leveraged when determining psychological arousal through EDA (Banganho et al. 2022).
The physical mechanism of EDA lies in the structure of the skin and its likeness to an electrical network of resistors and capacitors. The skin’s resistance varies according to ionic concentration in components like blood, sweat, and interstitial fluid, while membranes behave as capacitors by storing electric potential through ion-selective permeability. Sweat ducts contain ionic fluid, and upon sympathetic activation, increased eccrine sweat gland activity leads to changes in the skin’s electrical conductance. Since conductance is related to resistance inversely through the relationship conductance = 1/resistance, a decrease in electrical resistance through sweating increases skin conductance. These changes can be seen as an EDA signal, where the stimulus inducing the change in conductance is also causing the emotional arousal (Figure 1) (Banganho et al. 2022; Greco et al. 2016).
EDA ultimately provides an advantageous means of understanding human psychophysiology through the nervous system. While its longstanding role in research as a measure of physiological arousal has proven useful, it lacks the ability to distinguish between emotions and mental states. Further innovation and improvement in this area of diagnostics may yield results specifying emotional states and expand the breadth of its application in psychological and neurological assessments.
References
Banganho, Antonio, Marcelino Santos, and Hugo Placido da Silva. 2022. “Electrodermal Activity: Fundamental Principles, Measurement, and Application.” IEEE Potentials 41 (5): 35–43. https://doi.org/10.1109/mpot.2020.2983381.
Boucsein, Wolfram, Don C. Fowles, Sverre Grimnes, et al. 2012. “Publication Recommendations for Electrodermal Measurements.” Psychophysiology 49 (8): 1017–34. https://doi.org/10.1111/j.1469-8986.2012.01384.
Greco, Alberto, Gaetano Valenza, and Enzo Pasquale Scilingo. 2016. Advances in Electrodermal Activity Processing With Applications for Mental Health. Springer.
Posada-Quintero, Hugo F., and Ki H. Chon. 2020. “Innovations in Electrodermal Activity Data Collection and Signal Processing: A Systematic Review.” Sensors 20 (2): 479. https://doi.org/10.3390/s20020479.
Rahma, Osmalina Nur, Alfian Pramudita Putra, Akif Rahmatillah, et al. 2022. “Electrodermal Activity for Measuring Cognitive and Emotional Stress Level.” Journal of Medical Signals and Sensors 12 (2): 155–62. https://doi.org/10.4103/jmss.JMSS_78_20.
Winter, Michael, Rüdiger Pryss, Thomas Probst, and Manfred Reichert. 2020. “Towards the Applicability of Measuring the Electrodermal Activity in the Context of Process Model Comprehension: Feasibility Study.” Sensors 20 (16): 4561. https://doi.org/10.3390/s20164561.
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