Non-selective inhibition of the motor system following unexpected and expected infrequent events

Abstract

Motor inhibition is a key control mechanism that allows humans to rapidly adapt their actions in response to environmental events. One of the hallmark signatures of rapidly exerted, reactive motor inhibition is the non-selective suppression of cortico-spinal excitability (CSE): unexpected sensory stimuli lead to a suppression of CSE across the entire motor system, even in muscles that are inactive. Theories suggest that this reflects a fast, automatic, and broad engagement of inhibitory control, which facilitates behavioral adaptations to unexpected changes in the sensory environment. However, it is an open question whether such non-selective CSE suppression is truly due to the unexpected nature of the sensory event, or whether it is sufficient for an event to be merely infrequent (but not unexpected). Here, we report data from two experiments in which human subjects experienced both unexpected and expected infrequent events during a simple reaction time task while CSE was measured from a task-unrelated muscle. We found that expected infrequent events can indeed produce non-selective CSE suppression -but only when they occur during movement initiation. In contrast, unexpected infrequent events produce non-selective CSE suppression even in the absence of movement initiation. Moreover, CSE suppression due to unexpected events occurs at shorter latencies compared to expected infrequent events. These findings demonstrate that unexpectedness and stimulus infrequency have qualitatively different suppressive effects on the motor system. They also have key implications for studies that seek to disentangle neural and psychological processes related to motor inhibition and stimulus detection.

Towards a two-stage model of action-stopping: Attentional capture explains motor inhibition during early stop-signal processing

“…This is in line with the proposal that this ERP reflects a process that is unique to outright action-stopping (de Jong et al, 1990;Kok et al, 2004), and with the proposal that the onset latency of this ERP index the onset of processing that distinguishes successful from failed stopping (Wessel & Aron, 2015). Second, with regards to CSE suppression, these results confirm earlier studies showing that such effects can be observed not just after STOP signals, but also after surprising or merely infrequent events Dutra et al, 2018;Iacullo et al, 2020). The current results substantially add to these findings by demonstrating that STOP signals and IGNORE signals do not differ in the degree to which they suppress CSE early on (here, at 150ms post-stimulus).…”

“…The copyright holder for this preprint this version posted February 27, 2021. ; https://doi.org/10.1101/2021.02.26.433098 doi: bioRxiv preprint Non-selective CSE suppression. We first aimed to replicate the established findings of nonselective CSE suppression in the task related muscle following both STOP (Badry et al, 2009) and IGNORE signals (Iacullo et al, 2020). As can be seen in Figure 3 Time, there was only anecdotal evidence to support this difference (BF10 = 1.28, t(27) = 1.86, pHolm = .068, d = .35).…”

“…Non-selective CSE suppression. We first aimed to replicate the established findings of nonselective CSE suppression in the task related muscle following both STOP (Badry et al, 2009) and IGNORE signals (Iacullo et al, 2020). As can be seen in Figure 3 ( When STOP trials were distinguished by stopping success, further interesting patterns emerged.…”

“…The sample size was determined by an a priori analysis computed in G*Power (Faul et al, 2009) for repeated measures ANOVAs for 1 group and 3 measurements. Based on a recent study that showed non-selective CSE suppression in following infrequent events (Iacullo et al, 2020), we sought 80% power to identity a medium effect (f = .25) using a pre-defined alpha level of .05 (other G*power parameters were left to default). Two additional participants were collected to replace participants with insufficient trial counts.…”

“…Additionally, recent research on the presence of reactive, automatic inhibitory control following salient, surprising, or merely infrequent signals adds another layer of nuance to this discussion. Both EEG (Waller et al, 2019;Novembre et al, 2018; and CSE studies Dutra et al, 2018;Iacullo et al, 2020) have consistently shown that even without an instruction to stop an ongoing or impending action, such salient, surprising, or merely infrequent events automatically induce purportedly inhibitory signatures such as non-selective CSE suppression. This clearly raises the question of which purported inhibitory signatures are uniquely related to outright action-stopping, and which are observable after any type of salient event.…”