Significance of cognitive function in the elicitation of sympathetic skin response in healthy humans

The sympathetic skin response (SSR) is used as an index of sudomotor sympathetic function. However, the central processing of this response is not fully understood. To clarify this point, we assessed the relevance of cognitive function in the elicitation of SSR in 14 healthy subjects by recording simultaneously the somatosensory event-related potential (ERP) and SSR evoked by electric stimuli. The ERP paradigm consisted of three types of stimuli, task-relevant target, task-irrelevant electric shock which is equivalent to the common stimulus for eliciting SSR, and task-irrelevant standard stimuli. ERPs were recorded at Fz, Ct, and Pt on the scalp. SSRs were recorded in both palms and soles of the subject after each stimulus in the ERP paradigm. Target stimuli generated a P300 (P3b) and elicited a variety of SSRs from subject to subject. Electric shock stimuli generated a novelty P300 with a shorter peak latency and a higher amplitude than the P3b, with stable elicitation of SSR in the four limbs of all subjects. P300 amplitude showed a significant positive correlation with SSR amplitude with electric shock stimuli. This correlation predominated in the frontal region (Fz), as compared with the parietal region (Pt). A negative correlation between P300 latency and SSR amplitude with electric shock stimuli was also observed. These findings indicate that the elicitation of SSR is influenced by the generation of novelty P300, that is, cognitive function. The frontal region may play a key role in the elicitation of SSR. We believe that the assessment of novelty P300 is required for a precise interpretation of the SSR.