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Description: The recently proposed pause-then-cancel model (PTC) of action inhibition in humans proposes that inhibition unfolds in two stages: 1) a pause phase that exerts broad suppression over the whole motor system and 2) a cancel phase that entails more selective motor suppression to cancel or otherwise adjust ongoing movements (Diesburg & Wessel, 2021, Neurosci Biobehav Rev). In addition to proposing these distinct sources of inhibition, a key temporal assumption of the PTC model is that the pause phase peaks before the cancel phase. As a proxy for cortical spinal excitability (CSE), single-pulse transcranial magnetic stimulation (TMS) can be administered over M1 while recording surface electromyography from a stimulated muscle. Using this technique with the stop signal task, it is well documented that MEPs are reduced on successful stop compared to go trials both in task-relevant responding muscles and in completely task-irrelevant muscles (e.g., Badry et al., 2009, Clin Neurophysiol). We will have participants alternate between a manual and vocal stop-signal task while single-pulse TMS is administered to left M1 and MEPs are measured from the flexor digitorum superficialis (FDS). Importantly, this enables manipulating the task relevance of the FDS within-subjects using the same stimulus conditions and with stop signal tasks with similar time parameters (as suggested by literature and our own pilot study detailed in the Other section). We will thus examine both selective and non-selective CSE at three TMS stimulation times locked to the stop signal (150, 200, and 250 ms). We predict that additional selective suppression will be evident from the task-relevant muscle, indicating that stop-signals elicit both selective and non-selective suppression of CSE. We further predict that this selective suppression will become maximal at a later time point (e.g., 250 ms) than when non-selective CSE suppression is maximal (e.g., 150 or 200 ms). Finally, we will examine individual differences with the prediction that most individuals (by virtue of effect sizes) will show these patterns.