Formative Mechanism of Skin Potential Activity and Relationships between Skin Potential and Skin Impedance

Electrodermal activity (EDA) is well known as sensing emotional activity and autonomous nerve activity easily. There are skin resistance change (SRC), skin impedance change (SIC) and skin potential activity (SPA) for measurement of EDA. SPA consisted of skin potential level (SPL) and skin potential reflex (SPR) has been used well in recent years. However, there are various kinds of patterns in SPR, and not enough is known about the formative mechanism of SPA. Then, we examined these things. In the measurement of SPL, we require a rigid standard electrode accompanied by removing of stratum corneum. This treatment accompanies by some pain to subjects. Inadequate removing of the stratum corneum will tend to bring uncertainty of measurement result. Therefore, if the relationship between the degree of fall of SIL and fall of SPL accompanied by removing of stratum corneum are clarified, and sufficient removing for construction of standard electrode is checked by impedance, this approach is reasonable. Then we proposed, in the standard electrode site, the stratum corneum should be abraded when the skin impedance is less than about 0.8 kohm. The SPL of standard electrode expected to be under 2mV. Next, we proposed the equivalent electrical circuit model of measuring system for SPA, which was based on EDA model proposed by Edelberg. We described the complex SPR phenomena by the model. Furthermore, by the relation with environmental temperature, EDA measurements in various body surface parts were performed, and the relevance of thermal perspiration and mental perspiration was considered. The EDA in skin of palm and forearm were characterized by independency and a relationship between sweating due to thermal agents and sweating due to mental or sensory agents. The relativity of sweating at every point of human body to mental and sensory activity was emphasized at the high room temperature condition.