Electrodermal Activity (EDA)
Even though we are not aware of it, our skin is active most of the time, in the sense that it’s electrical properties such as the skin conductance and the skin potential change over time and display waves which can occur every few seconds. The seat of this phenomenon is mainly the sweating.
Electrical equivalent model of skin admittance and skin potential (left) and an example skin conductance measurement of the same subject during different levels of stress (right).
The electrical conductance of the outermost layer of dead skin cells is very low, but when sweat is expulsed through the sweat ducts, the conductance increases rapidly, also leading to a change in the skin potential. As the sweating is governed by the sympathetic nervous system, this measurement provides an indirect but sensitive and non-invasive representation of the sympathetic nervous activity, especially when measuring in the palms where this sensitivity is highest. As shown by example in the above figure to the right, there are generally few skin conductance waves during relaxation (blue), but the activity is much higher during stress (red).
This type of measurement has been suggested for a vast array of medical applications including hyperhidrosis, epilepsy, anesthesia, diabetes and neuropsychiatry to name a few areas.
In order to provide the best clinical use of this technology, it is important to have a good knowledge about what we are measuring, and the sources of errors are many. This includes proper use of electrodes, proper instrumentation and proper interpretation of the signals.
Oslo Bioimpedance Group has conducted research on electrodermal activity for more than 30 years, and has contributed significantly to the understanding we have today of this phenomenon. Our group has developed the first portable multichannel skin AC conductance device, and is continuously performing basic research and further developing the measuring technology.