Somatosensory pain is not reliably modulated by weak acoustic stimuli.

Background: Pain induced by electrical stimuli has been found in previous research to be reduced by brief, weak electrical pulses, termed prepulses, presented 40 to 60ms prior to the painful electrical stimulus.

Methods: The present experiment investigated the generality of this effect by presenting weak acoustic stimuli simultaneously with, or 80 or 1000ms prior to, painful electric shocks. In the second half of the experimental session, each participant (N=119) was told that the acoustic stimuli would either increase or decrease the pain induced by the electric shock, to investigate automatic and controlled cognitive processes in the modulation of pain.

Results: Acoustic stimuli presented simultaneously with painful stimulation increased pain slightly (4mm on a 100mm scale). Acoustic stimuli presented 80 and 1000ms prior to painful stimuli had no effect on pain. Information that acoustic stimuli would increase pain did so in females, but only when the acoustic stimulus was presented 80ms prior to the painful stimulus.

Conclusions: The effect of the acoustic stimuli and of information was weak. Failure to replicate previous findings of decreased pain by weak prepulses was most likely due to the sensory modality of the prepulse stimuli. It is recommended that further studies of pain modulation by brief stimulation use electrical and not acoustic prepulse stimuli.