Cortical Contributions to Attentional Orienting and Response Cancellation in Action Stopping.

Action cancellation involves the termination of planned or ongoing movement, likely initiated in the cortex by the pre-supplementary motor area (preSMA) and inferior frontal gyrus (IFG). It is frequently examined using the stop-signal task; electromyography (EMG) studies have shown action cancellation (in stop trials) can involve the partial activation of the responding muscles, which does not result in an overt behavioral response. The neural correlates of these partial responses are not well understood. Here, we combined functional near-infrared spectroscopy (fNIRS) and EMG to examine the neural correlates of terminated actions (partial responses) in a response- and stimulus-selective stop signal task, controlling for attentional confounds by comparing neural activity in stop and ignore trials. fNIRS analyses revealed increased preSMA activity in successful stop compared to ignore trials, but no such differences in the IFG, consistent with postulations that the preSMA is involved uniquely in action cancellation, while the IFG responds generically to unexpected stimuli. Critically, preSMA activity was greater in trials without partial muscle activation, potentially due to proactive inhibitory processes pre-emptively suppressing motor output in these trials. These findings advance understanding of some of the neurophysiological dynamics involved in action cancellation and highlight the utility of combining fNIRS with EMG in this domain.