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Non-thermal sweating in humans: an investigation of mental sweating from non-glabrous skin surfaces

C.A. Machado-Moreira, J.N. Caldwell, A.K. Meijer, F. Wilmink and N.A.S. Taylor, School of Health Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.

Human eccrine sweat glands are cholinergically innervated, possibly being transformed from adrenergic pathways during postnatal development. Some glabrous (non-hairy) regions receive cholinergic and adrenergic stimulation. Such sites are powerfully influenced by changes in mental or emotional states, but it is generally regarded that non-glabrous surfaces do not participate in such sweating. Herein are reported experiments to test the hypothesis that non-thermal (mental) sudomotor drive in the heat would elevate sweat secretion from non-glabrous surfaces of the head. Ten, resting (sitting) males were heated using a water-perfusion suit (46°C) and a climate-controlled chamber (36°C, 60% relative humidity). Subjects were shaved and instrumented. Mean body temperature was elevated (1.9°C) to induce generalised thermal sweating. Sweat rate was measured (0.2 Hz: 3.16 cm2 capsules) at ten sites (forehead plus nine sites inside the hair line). After 25 min, subjects performed a cognitive-function task, requiring considerable concentration and mental effort. Sudomotor responses were evaluated during 5 min preceding (20-25 min), and 2 min immediately after that task (25-27 min). Since mean body temperature changes were minimal from 20-27 min (<0.04°C), differences in sudomotor sensitivity (over time) between these two periods were compared. At all sites, the mental task increased this sensitivity at least 5.5-fold, with these differences being significant (P<0.05), except at the occipital region. These observations demonstrate that the non-thermal (mental) sudomotor drive is not restricted just to glabrous skin. We are currently investigating the extent of this phenomenon, and its neuropharmacological significance.