To Act and Not to Act: Multimodal Investigations of Selective Stopping

Abstract

Selective stopping is a complex form of response inhibition where a person must execute and cancel part of an action at the same time. A need for selective stopping can emerge in behaviours that require the coordination of multiple effectors guided by various stimuli. The complexity of selective stopping is exemplified by a persistent response delay in an action’s executed (non-stopped) components. This stopping-interference effect may arise from a global response inhibition mechanism. However, behavioural observations indicate that the magnitude of the stopping-interference effect is modifiable. This thesis aimed to determine the neural basis and modulating factors of response inhibition during selective stopping. A multimodal approach was used across four studies with healthy adult human participants, selective stopping paradigms, and electrophysiological measures of response inhibition from electroencephalography (EEG), transcranial magnetic stimulation (TMS), and electromyography (EMG). In the first study, stopping-interference was less during decoupled than coupled responses, but both were marked by a nonselective increase in sensorimotor beta-power measured with EEG. In the second study, informative selective stopping cues led to less stopping-interference through proactive adjustments to the stopped and non-stopped hand measured with EMG. However, cue-related improvements in stopping selectivity were not matched by concomitant modulation of facilitatory or inhibitory interhemispheric influences measured with TMS. A novel selective stopping toolbox was presented in the third study. Behavioural comparisons between two prominent selective stopping paradigms demonstrated that anticipatory variants favour experiments requiring strict control of response times. In contrast, stop-signal variants favour experiments where modelling of response inhibition latency is required. In the fourth experiment, beta-bursts measured with EEG and gammaaminobutyric acid (GABA)-mediated inhibition measured with TMS were increased nonselectively after selective stop and ignore signals, while the overall stopping-interference effect was twice as large in the former. Together, these studies indicate that the stoppinginterference effect is a ubiquitous feature of selective stopping generated by nonselective response inhibition but modifiable based on response preparation. The findings from this thesis exemplify how investigating response inhibition can provide new insights into the cognitive control of action.