The Galvanic Skin Response (GSR) is defined as a change in the electrical properties of the skin. The signal can be used for capturing the autonomic nerve responses as a parameter of the sweat gland function. The measurement is relatively simple, and has a good repeatability. Therefore the GSR measurement can be considered to be a simple and useful tool for examination of the autonomous nervous system function, and especially the peripheral sympathetic system.
Several terms are used for this phenomena, such as EDA (electrodermal activity), EDR (electrodermal response), EDL (electrodermal level), SCA (skin conductance activity), SCR (skin conductance response), and a lot more.
Out of the number of terms used for this phenomenon, it is clear that GSR has more than one property. It can be described in terms of conductance, resistance and electro¬physiological potential. The electro-physiological signal is generated by the sweat glands, and the sweat is probably the origin of the variation in resistance and conductivity, although the vaso-dilatation and -constriction may also play an important role.
In most cases, the GSR is measured using a part of the skin having a lot of sweat glands. As a reference you can use a part of the skin with less or no sweat glands, or measure in the same area as the active electrode.