Characteristics of habituation of the sympathetic skin response to repeated electrical stimuli in man

Objectives: To study the effect of repeating electrical peripheral nerve st imulation on latency, duration and amplitude of the sympathetic skin respon se (SSR). Methods: SSRs were elicited in all limbs by median and peroneal nerves stim uli. In 10 subjects, 20 stimuli were applied at random time intervals (15-2 0 s). Another test was performed in 7 subjects using the same protocol, but switching the stimulation site every 5 or 10 stimuli without warning. Results: The mean amplitude of right palmar response to right peroneal nerv e stimulation decreased from 5.05 +/- 0.76 (SEM) mV at the first stimulus t o 1.23 +/- 0.42 mV at the 20th stimulus (P < 0.001). The latency did not ch ange significantly (1473 +/- 82 to 1550 +/- 90 ms, P > 0.1), while the dura tion increased (1872 +/- 356 to 3170 +/- 681 ms, P < 0.001). Stimulation an d recording at other sites showed similar trends. Changing the stimulation site failed to alter the adaptation process in terms of amplitude, latency or duration. Conclusions: Changes in amplitude and duration of the SSRs to repeated elec trical stimuli can occur in presence of constant latency and appear to be i ndependent of the source of sensory input. Peripheral sweat gland mechanism s may be involved in the loss of amplitude and increase in duration of the SSR during habituation. (C) 2001 Published by Elsevier Science Ireland Ltd.