The psycho-galvanic reflex: a pharmacological study of the peripheral mechanism.

The psycho-galvanic reflex is a decrease in the electrical resistance of the skin which occurs in response to a wide variety of stimuli. The physiological basis of this autonomic measure, known also as the galvanic skin response or electro-dermal response, has not yet been fully elucidated. There are two principal theories accounting for the phenomenon. The vascular theory, proposed by Fire (1888) and elaborated by McDowall (1933), maintains that it is caused by a change in tone of the blood vessels of the skin. The second theory, with many more adherents, was advanced by Tarchanoff (1890), who suggested that it was due to changes in the secretory activity of the sweat glands. This was later modified to changes in the pre-secretory activity of the sweat glands, and the studies of Darrow (1927) lent strong support to this view. Investigators who have tested the secretory theory have sought to do so by attempting to prevent secretory activity by means of atropine. The results, however, have been conflicting, as exemplified by two of the more recent investigations in this field. In the first of these Carmichael, Honeyman, Kolb, and Stewart (1941) found that local atropinization by iontophoresis did not abolish the psychogalvanic reflex. On the other hand, Montagu (1958), using the same technique and dosage, obtained opposite results. The vascular theory has been tested by determining the effect on the psycho-galvanic reflex of exsanguinating an extremity with an Esmarch's bandage. By this means workers have succeeded in producing either a marked reduction (Carmichael et al., 1941) or complete abolition (Goadby and Goadby, 1949) of the psycho-galvanic reflex. The recent introduction of post-ganglionic, adrenergic, neurone-blocking agents such as bretylium (N-o-bromobenzyl-Nethyl-NN-dimethyl-ammonium) seemed to the authors to afford a more convenient means of modifying vasomotor activity. The object of this paper is to report two series of experiments in which the skin resistance and the pulse volume were recorded simultaneously from the same finger. In one series, atropine was administered locally by iontophoresis in order to paralyse the cholinergically innervated sweat glands; in the other, bretylium was used in a similar fashion to paralyse the adrenergic nerve endings governing vasomotor tone.