Should we split? Using covert muscle activation as a mean to separate action cancellation processes in a novel stop signal task : a behavioural and neuroimaging study

The ability to cancel already initiated movement in response to new stimuli is crucial for traversing our world. Common testing of individuals using the Stop-Signal Task (SST) uses an adaptive ‘staircase’ of stop signal presentation to achieve 50% accuracy on stop trials to ensure reactive responses. However, this staircasing of signal presentation may be confounding behavioural and cortical results due to the potential inclusion of trials that did not require activation of the inhibitory network. Through electromyography (EMG) researchers can register when a participant executed a partial burst of muscle activation that was cancelled before the movement was finalised (a partial burst). In this study, participants (N=30) completed a variant of the SST whilst attached to EMG and fNIRS equipment to measure partial burst presence and cortical activation levels between three distinct brain regions. Subsequent EMG data was used to partition trials by the presence of partial bursts to assess if significant behaviour and cortical differences could be found between trials with and without partial EMG activation. Behavioural results indicate that when partitioned by partial burst presence, that both ignore and stop trials had significantly slower reaction times than trials without partial bursts (p<.001). Qualitative inspection of fNIRS traces revealed possible significant differences in activation levels between successful stop trials with and without partial bursts, and minimal activation level difference in ignore trials with and without partial bursts. Specific brain regions were associated with neurally distinct activations for both stop and ignore trials with and without partial bursts.