Modulation of short intra-cortical inhibition during action reprogramming.

Actions are selected in the context of environmental demands and internal goals. Since both change continuously it is often necessary to inhibit a prepared action plan in favour of an alternative, a process we refer to as action reprogramming. Previous studies have established that a frontal/basal ganglia network exerts top-down control over the primary motor cortex (M1) during action reprogramming. The current study focuses on the role of M1 itself during action reprogramming. Participants were asked to perform a behavioural task that required them to either execute a prepared response or to reprogram an alternative response. Paired-pulse TMS was used to investigate short-interval intra-cortical inhibition (SICI) during these action execution and action reprogramming trials. Normal action execution was associated with sustained SICI in the M1 during both trials in which the contralateral hand was to respond and trials in which the ipsilateral hand was to respond. In contrast, reprogramming towards an alternative action was associated with a progressive release of SICI in M1 involved in the execution of the novel response. This release started 125 ms after the cue telling the participants to reprogram their action. This time point is consistent with previous results showing a facilitatory influence of the pre-supplementary motor area (pre-SMA) on the M1 at the same delay. Hence, SICI might be a potential candidate mechanism through which frontal lobe areas could influence primary motor cortex output.