A TMS investigation of the Perruchet effect

This study sought to investigate how corticospinal excitability (CE) was influenced during the Perruchet effect. In the Perruchet effect a single stimulus (the conditioned stimulus, CS) is paired with a second stimulus (the unconditioned stimulus, US) on half the trials and on the other half the trials the US is not presented. Conditioned responding to the CS is typically found to dissociate from conscious expectancy for the US. In this experiment there were two USs, one requiring participants to make a speeded reaction time response and another the withholding of said response. In order to study changes in CE, motor evoked potentials (MEPs) were recorded as a product of single pulse transcranial magnetic simulation (TMS) applied to the primary motor cortex at different time points throughout the task. Different stimulation points were used to assess whether changes in CE were dictated by CS-US pairings or whether a different mechanism unrelated to the CS was responsible for motor preparation.