Local cold effect on the excitability recovery curve of the sympathetic skin response

The sympathetic skin response (SSR) is an established technique used to assess the activity of the sympathetic sudomotor pathway, but it is limited in application by the habituation process. The nature of habituation is not clear. In this study we aimed to further understand the role of the peripheral mechanism in the habituation of the SSR. We recorded SSRs to paired stimuli with interstimulus intervals of 1, 2, 3, 4 and 5 seconds on both hands of 15 volunteers simultaneously, while the right hand was cooled to 23-24 degrees C and the left hand was between 32 and 33 degrees C. The amplitude and latency generated by the first stimulus (SSR1) and the second stimulus (SSR2) were measured. While SSR2 first occurred at ISI 2 in 7 subjects and ISI 3 in 8 subjects on the normal side, SSR2 first occurred at ISI 4 in 7 subjects and ISI 3 in 8 subjects on the cooled side. The SSR amplitude recovery percentage, which was obtained by dividing the amplitude of SSR2 by the amplitude of SSR1, was significantly different on the cooled side. No significant differences were found between SSR1 and SSR2 latencies, which were measured at ISI 3, 4 and 5 on the normal side and at ISI 5 on the cooled side. Our findings further support that a peripheral component might be involved in the modification and habituation of the SSR in terms of amplitude, but not of latency.