The effects of acoustic startle on sensorimotor attenuation prior to movement.

A startling auditory stimulus delivered unexpectedly can activate subcortical structures triggering a prepared movement involuntarily and shortening reaction times. We investigated the effects of the startle acceleration of response on sensory suppression, a phenomenon linked to the voluntary motor command whereby a tactile stimulus is less likely to be perceived on a moving body-part prior to voluntary movement than at rest. Subjects had to detect weak shocks which were delivered to the index finger after a Go signal on some trials. We found that detection rates on movement trials were lower than on non-movement trials, consistent with sensory suppression. In addition, a loud acoustic stimulus was presented at the same time as the Go signal on some trials (startle trials). Reaction times were significantly shorter on startle trials than on other trials, replicating previous startle acceleration of reaction time effects attributed to the operation of subcortical pathways. However, we found no overall difference in premovement sensory suppression effects between baseline and startle movement trials. Rather, startle acceleration of voluntary reactions produced a corresponding acceleration of sensory suppression. Our results provide evidence for a subcortical contribution to sensory suppression and suggest that sensory suppression is a highly general form of motor and sensory interaction.