Evoked autonomic skin potentials (Present views of the mechanisms)

This article presents the present views on the mechanisms of the evoked autonomic skin potentials (EASP). Consideration is given to the research history of the electrodermal phenomena, methodological features of EASP recording, and possibilities of their implementation in clinical neurology. The EASP is a suprasegmental somatoautonomic reflex, whose effector is presented by sweat glands, and the posterior hypothalamus acts as a response “generator.” Besides the afferent and efferent parts, the reflex arc includes the hierarchical CNS structures that modulate the response expression. The EASP recorded from healthy humans in supine position in the state of rest under the usual ambient temperature is presented by a triphase curve. The first phase is manifested by a slight positive deflection from the baseline. It is associated with the initial decrease in perspiration in response to stimulation. The amplitude of this deflection reflects the activity of the hypothalamic centers that inhibit perspiration and is a measure of parasympathetic activity. The following second phase consists of the ascending and descending parts. The ascending part reflects the increase in perspiration in response to stimulation and is represented by a pronounced negative deflection of the potential. The descending part of the second phase is associated with the recovery of the normal (tonic) perspiration level. The amplitude of the second phase reflects the activity of the suprasegmental (primarily, hypothalamic) sympathetic centers. The third phase represents the trace wave, the mechanisms of which are still vague. The EASP latencies reflect a synaptic delay in the structures of the CNS and ganglia of the sympathetic trunk as well as the time of impulse conduction by the postganglionic sympathetic fibers. The EASP changes under conditions of exposure to high temperature and humidity and under the influence of some drugs (Reserpine [Rauwolfia alcaloid], Pyrroxanum, Sydnocarb [syn. Mesocarbum], Aethimizolum, Gammalon [syn. Aminalonum, GABA], and Phenazepamum) are considered.