Prepulses reduce the pain of cutaneous electrical shocks

Objective: Both the startle reflex elicited by an intense acoustic or tactile stimulus and the perceived intensity of that stimulus can be diminished by a weak "prepulse" that precedes the startling stimulus. The present study examined whether prepulses can also diminish the pain produced by an intense electrical stimulus similar to that used to treat life-threatening cardiac arrhythmias in conscious patients with implantable cardioverter/defibrillators or transcutaneous pacemakers. Methods: Perceptual and pain thresholds for electrical shocks to the arm were determined in 20 adults. Participants then rated the painfulness of 25 electrical shocks that were 1.5 times the pain threshold (mean shock intensity, approximate to 160 V) and either presented alone or preceded (at 40-60 ms) by weak electrical prepulses equal to or 25% above the perceptual threshold, Results: Prepulses significantly reduced the pain produced by the intense shocks. Individuals with the lowest pain thresholds experienced the greatest pain reduction with prepulses, In these more sensitive individuals, the most effective prepulses reduced perceived pain by 26% across the entire test session and by 54% in the initial block of five shocks, Conclusions: Prepulses may be useful in diminishing the pain associated with the therapeutic electrical shocks used to treat cardiac arrhythmias.