A global pause generates nonselective response inhibition during selective stopping

Common and unique neurophysiological signatures for the stopping and revising of actions reveal the temporal dynamics of inhibitory control

Inhibitory control is a crucial cognitive-control ability for behavioral flexibility that has been extensively investigated through action-stopping tasks. Multiple neurophysiological features have been proposed to represent 'signatures' of inhibitory control during action-stopping, though the processes signified by these signatures are still controversially discussed. The present study aimed to disentangle these processes by comparing simple stopping situations with those in which additional action revisions were needed. Three experiments in female and male humans were performed to characterize the neurophysiological dynamics involved in action-stopping and - changing, with hypotheses derived from recently developed two-stage 'pause-then-cancel' models of inhibitory control. Both stopping and revising an action triggered an early broad 'pause'-process, marked by frontal EEG β-bursts and non-selective suppression of corticospinal excitability. However, partial-EMG responses showed that motor activity was only partially inhibited by this 'pause', and that this activity can be further modulated during action-revision. In line with two-stage models of inhibitory control, subsequent frontocentral EEG activity after this initial 'pause' selectively scaled depending on the required action revisions, with more activity observed for more complex revisions. This demonstrates the presence of a selective, effector-specific 'retune' phase as the second process involved in action-stopping and -revision. Together, these findings show that inhibitory control is implemented over an extended period of time and in at least two phases. We are further able to align the most commonly proposed neurophysiological signatures to these phases and show that they are differentially modulated by the complexity of action-revision.

Selective cancellation of reactive or anticipated movements: Differences in speed of action reprogramming, but not stopping

The ability to inhibit movements is an essential component of a healthy executive control system. Two distinct but commonly used tasks to assess motor inhibition are the stop signal task (SST) and the anticipated response inhibition (ARI) task. The SST and ARI tasks are similar in that they both require cancelation of a prepotent movement; however, the SST involves cancelation of a speeded reaction to a temporally unpredictable signal, while the ARI task involves cancelation of an anticipated response that the participant has prepared to enact at a wholly predictable time. 33 participants (mean age = 33.3 years, range = 18-55 years) completed variants of the SST and ARI task. In each task, the majority of trials required bimanual button presses, while on a subset of trials a stop signal indicated that one of the presses should be cancelled (i.e., motor selective inhibition). Additional variants of the tasks also included trials featuring signals which were to be ignored, allowing for insights into the attentional component of the inhibitory response. Electromyographic (EMG) recordings allowed detailed comparison of the characteristics of voluntary action and cancellation. The speed of the inhibitory process was not influenced by whether the enacted movement was reactive (SST) or anticipated (ARI task). However, the ongoing (non-cancelled) component of anticipated movements was more efficient than reactive movements, as a result of faster action reprogramming (i.e., faster ongoing actions following successful motor selective inhibition). Older age was associated with both slower inhibition and slower action reprogramming across all reactive and anticipated tasks.

Stopping Speed in Response to Auditory and Visual Stop Signals Depends on Go Signal Modality

Past research has found that the speed of the action cancellation process is influenced by the sensory modality of the environmental change that triggers it. However, the effect on selective stopping processes (where participants must cancel only one component of a multicomponent movement) remains unknown, despite these complex movements often being required as we navigate our busy modern world. Thirty healthy adults (mean age = 31.1 years, SD = 10.5) completed five response-selective stop signal tasks featuring different combinations of "go signal" modality (the environmental change baring an imperative to initiate movement; auditory or visual) and "stop signal" modality (the environmental change indicating that action cancellation is required: auditory, visual, or audiovisual). EMG recordings of effector muscles allowed detailed comparison of the characteristics of voluntary action and cancellation between tasks. Behavioral and physiological measures of stopping speed demonstrated that the modality of the go signal influenced how quickly participants cancelled movement in response to the stop signal: Stopping was faster in two cross-modal experimental conditions (auditory go - visual stop; visual go - auditory stop), than in two conditions using the same modality for both signals. A separate condition testing for multisensory facilitation revealed that stopping was fastest when the stop signal consisted of a combined audiovisual stimulus, compared with all other go-stop stimulus combinations. These findings provide novel evidence regarding the role of attentional networks in action cancellation and suggest modality-specific cognitive resources influence the latency of the stopping process.

Corticospinal excitability reductions during action preparation and action stopping in humans: Different sides of the same inhibitory coin?

Motor functions and cognitive processes are closely associated with each other. In humans, this linkage is reflected in motor system state changes both when an action must be prepared and stopped. Single-pulse transcranial magnetic stimulation showed that both action preparation and action stopping are accompanied by a reduction of corticospinal excitability, referred to as preparatory and response inhibition, respectively. While previous efforts have been made to describe both phenomena extensively, an updated and comprehensive comparison of the two phenomena is lacking. To ameliorate such deficit, this review focuses on the role and interpretation of single-coil (single-pulse and paired-pulse) and dual-coil TMS outcome measures during action preparation and action stopping in humans. To that effect, it aims to identify commonalities and differences, detailing how TMS-based outcome measures are affected by states, traits, and psychopathologies in both processes. Eventually, findings will be compared, and open questions will be addressed to aid future research.

Examining motor evidence for the pause-then-cancel model of action-stopping: Insights from motor system physiology

Stopping initiated actions is fundamental to adaptive behavior. Longstanding, single-process accounts of action-stopping have been challenged by recent, two-process, 'pause-then-cancel' models. These models propose that action-stopping involves two inhibitory processes: 1) a fast Pause process, which broadly suppresses the motor system as the result of detecting any salient event, and 2) a slower Cancel process, which involves motor suppression specific to the cancelled action. A purported signature of the Pause process is global suppression, or the reduced corticospinal excitability (CSE) of task-unrelated effectors early on in action-stopping. However, unlike the Pause process, few (if any) motor system signatures of a Cancel process have been identified. Here, we used single- and paired-pulse TMS methods to comprehensively measure the local physiological excitation and inhibition of both responding and task-unrelated motor effector systems during action-stopping. Specifically, we measured CSE, short-interval intracortical inhibition (SICI), and the duration of the cortical silent period (CSP). Consistent with key predictions from the pause-then-cancel model, CSE measurements at the responding effector indicated that additional suppression was necessary to counteract Go-related increases in CSE during-action-stopping, particularly at later timepoints. Increases in SICI on Stop-signal trials did not differ across responding and non-responding effectors, or across timepoints. This suggests SICI as a potential source of global suppression. Increases in CSP duration on Stop-signal trials were more prominent at later timepoints. SICI and CSP duration therefore appeared most consistent with the Pause and Cancel processes, respectively. Our study provides further evidence from motor system physiology that multiple inhibitory processes influence action-stopping.