Cortical activation during temporal preparation assessed by transcranial magnetic stimulation

Preparatory modulations relative to the timing of upcoming stimuli may involve activation or suppression mechanisms. Here, we assessed the interplay between these mechanisms with transcranial magnetic stimulation (TMS) of the motor cortex. Single- or paired-pulse TMS with 3- or 15-ms interstimulus intervals was delivered during the interval between the warning and the imperative stimuli (i.e., the foreperiod) of a choice reaction time task. Temporal uncertainty was manipulated through between-block variation of the foreperiod duration (500 or 2500 ms). The shortening of reaction time for the short foreperiod was accompanied with a decrease in amplitude of the single-pulse motor evoked potential (MEP), indicating corticospinal suppression. The co-occurring increase in amplitude of both paired-pulse MEPs (3 and 15 ms) expressed relative to single-pulse MEPs reveals released short intracortical inhibition (SICI) and enhanced intracortical facilitation (ICF). These results suggest that temporal preparation is associated with both corticospinal suppression and cortical activation.

Research highlights▶ Reduction of temporal uncertainty shortened choice reaction time. ▶ Single-pulse MEP evoked by TMS of the motor cortex decreased during the foreperiod. ▶ Conditioned paired-pulse MEPs (3 and 15 ms) increased during the foreperiod. ▶ Corticospinal suppression and cortical activation occur during temporal preparation. ▶ Activation involves released cortical inhibition and enhanced cortical facilitation.