Within-subject consistency of sympathetic-skin-response waveform across different modalities of stimulation

This study was conducted to investigate the intra-subject consistency of the waveform type and the size of the sympathetic skin response (SSR) evoked by different modalities of stimulation. Thirty-eight normal volunteers were enrolled as subjects. SSRs were obtained using three different modalities of stimulations: auditory (a-SSR), electrical (e-SSR), and magnetic (m-SSR). Four stimuli of each modality were applied. The waveforms were classified into two types, P (positive component larger the than negative component) and N (vice versa). P-type waveforms were less frequent in the a-SSR than in the e- and m-SSR. The occurrence of the respective waveforms and the values of maximum amplitudes were significantly correlated among the SSRs evoked by different types of stimulation. Judging from these results, the SSR waveforms and size seemed to be consistent in individuals. The results also suggested that endogenous factors in an individual related to the development of SSRs e.g., individual's emotional state, susceptibility to the surprise effect, and anatomical characteristic were important determinants of the SSR waveforms and maximum amplitude.