Investigating the role of contextual cues and interhemispheric inhibitory mechanisms in response-selective stopping: a TMS study

Abstract

Response-selective stopping requires cancellation of only one component of a multicomponent action. While research has investigated how delays to the continuing action components ("stopping interference") can be attenuated by way of contextual cues of the specific stopping demands ("foreknowledge"), little is known of the underlying neural mechanisms. Twenty-seven, healthy, young adults undertook a multicomponent stop-signal task. For two thirds of trials, participants responded to an imperative (go) stimulus (IS) with simultaneous button presses using their left and right index fingers. For the remaining one third of trials, the IS was followed by a stop-signal requiring cancellation of only the left, or right, response. To manipulate foreknowledge of stopping demands, a cue preceded the IS that informed participants which hand might be required to stop (proactive) or provided no such information (reactive). Transcranial magnetic stimulation (TMS) assessed corticospinal excitability (CSE) as well as short- and long-interval interhemispheric inhibition (SIHI, LIHI) between the primary motor cortices. Proactive cues reduced, but did not eliminate, stopping interference relative to the reactive condition. Relative to TMS measures at cue onset, decreases in CSE (both hands and both cue conditions) and LIHI (both hands, proactive condition only) were observed during movement preparation. During movement cancellation, LIHI reduction in the continuing hand was greater than that in the stopping hand and greater than LIHI reductions in both hands during execution of multicomponent responses. Our results indicate that foreknowledge attenuates stopping interference and provide evidence for a novel role of LIHI, mediated via prefrontal regions, in facilitating continuing action components.

Keywords: Bayes; Inhibitory control; Interhemispheric inhibition; Response inhibition; Selective stopping; Transcranial magnetic stimulation.

Fig. 1

Experimental trials. Participants were visually presented, on a computer screen, a multicomponent stop-signal task, comprising of go trials (2/3^rd of all trials) and stop trials (1/3^rd of all trials). On go trials, an imperative signal (IS) of green arrows pointing to the left (“<”) and right (“>”) required participants to make a bimanual response using their left and right index fingers. On response-selective stop trials, after a stop-signal delay, either the left (left stop) or right (right stop) green IS arrow turned red, requiring participants to cancel their left, or right, index finger, respectively, while continuing to press the other button. In both go and stop trials, the IS was preceded by a warning signal (WS) that was either uninformative (fixation cross: +), probing a) reactive response-selective stopping, or informative (Maybe Stop Left: MSL; Maybe Stop Right: MSR), probing b) proactive response-selective stopping, about potential upcoming stopping demands. Numbers, in parentheses, below trial types indicate total trial numbers and filled lightning bolts indicate one of the four possible time-points (WS, IS, IS150, and SS150) at which TMS was administered on a single trial, noting that SS150 was only possible on stop trials

Fig. 2

Behavioural measures. Boxplots depict, on the ordinate, a) the correct RT (in milliseconds) for go trials (solid), stop trials with RT relative to the imperative signal (dashed), and stop trials with RT relative to the stop-signal (dotted), as well as b) stop-signal reaction-time, for the proactive and reactive conditions. Lower and upper hinges depict the 25^th and 75^th percentile respectively with the lower and upper whiskers depicting values 1.5 times the interquartile range (defined as the distance between the 25^th and 75^th percentile) below and above the hinges, respectively. Data beyond the whiskers are plotted as filled circles

Fig. 3

Neurophysiological measures. Boxplots depict, on the ordinate, a) CSE (in mV), and b) LIHI ratio, at the warning signal (WS), imperative signal (IS), 150 ms after the IS (IS150) and stop-signal (SS150) time-points on the abscissa. These are plotted for various hand statuses, specifically at WS when there is no relevant foreknowledge (unfilled dotted), at IS (proactive condition leading to definitely going—light grey solid—and maybe stopping—dark grey solid, and reactive condition leading to unknown—unfilled solid), at IS150 when the imperativeness of the go-signal dominates (light grey dotted), and at SS150 (continuing hand: light grey dashed; stopping hand: dark grey dashed). LIHI ratios less than and greater than 1 represent inhibitory and facilitatory interactions, respectively. Lower and upper hinges depict the 25^th and 75^th percentile respectively with the lower and upper whiskers depicting values 1.5 times the interquartile range (defined as the distance between the 25^th and 75^th percentile) below and above the hinges, respectively. Data beyond the whiskers are plotted as filled circles