Regional brain responses associated with thermogenic and psychogenic sweating events in humans
Sweating events occur in response to mental stress (psychogenic) or with increased body temperature (thermogenic). We previously found that both were linked to activation of common brain stem regions, suggesting that they share the same output pathways: a putative common premotor nucleus was identified in the rostral-lateral medulla (Farrell MJ, Trevaks D, Taylor NA, McAllen RM. Am J Physiol Regul Integr Comp Physiol 304: R810-R817, 2013). We therefore looked in higher brain regions for the neural basis that differentiates the two types of sweating event. Previous work has identified hemispheric activations linked to psychogenic sweating, but no corresponding data have been reported for thermogenic sweating. Galvanic skin responses were used to measure sweating events in two groups of subjects during either psychogenic sweating (n = 11, 35.3 ± 11.8 yr) or thermogenic sweating (n = 11, 34.4 ± 10.2 yr) while regional brain activation was measured by BOLD signals in a 3-Tesla MRI scanner. Common regions activated with sweating events in both groups included the anterior and posterior cingulate cortex, insula, premotor cortex, thalamus, lentiform nuclei, and cerebellum (Pcorrected < 0.05). Psychogenic sweating events were associated with significantly greater activation in the dorsal midcingulate cortex, parietal cortex, premotor cortex, occipital cortex, and cerebellum. No hemispheric region was found to show statistically significantly greater activation with thermogenic than with psychogenic sweating events. However, a discrete cluster of activation in the anterior hypothalamus/preoptic area was seen only with thermogenic sweating events. These findings suggest that the expected association between sweating events and brain regions implicated in "arousal" may apply selectively to psychogenic sweating; the neural basis for thermogenic sweating events may be subcortical.