Evidence for Two Concurrent Inhibitory Mechanisms during Response Preparation

Abstract

Inhibitory mechanisms are critically involved in goal-directed behaviors. To gain further insight into how such mechanisms shape motor representations during response preparation, motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) and H-reflexes were recorded from left hand muscles during choice reaction time tasks. The imperative signal, which indicated the required response, was always preceded by a preparatory cue. During the postcue delay period, left MEPs were suppressed when the left hand had been cued for the forthcoming response, suggestive of a form of inhibition specifically directed at selected response representations. H-reflexes were also suppressed on these trials, indicating that the effects of this inhibition extend to spinal circuits. In addition, left MEPs were suppressed when the right hand was cued, but only when left hand movements were a possible response option before the onset of the cue. Notably, left hand H-reflexes were not modulated on these trials, consistent with a cortical locus of inhibition that lowers the activation of task-relevant, but nonselected responses. These results suggest the concurrent operation of two inhibitory mechanisms during response preparation: one decreases the activation of selected responses at the spinal level, helping to control when selected movements should be initiated by preventing their premature release; a second, upstream mechanism helps to determine what response to make during a competitive selection process.

Age-related differences in corticospinal excitability during a choice reaction time task

“…The most reasonable interpretation of these findings is that slowing in RTs among older individuals is directly associated with a decline in preparatory processes in the dominant hemisphere. Evidence from earlier studies showed that decrease of RTs in short (500-1,000 ms) preparatory periods is accompanied by reduction in CS excitability at the expected onset of the imperative stimulus (Davranche et al 2007;Duque and Ivry 2009;Duque et al 2010;Fujiyama et al 2011;Hasbroucq et al 1997Hasbroucq et al , 1999Hammond 2008, 2009;Tandonnet et al 2003Tandonnet et al , 2010). In the current study, lower suppression of MEPs yet longer RTs in the older individuals may appear seemingly contradictory.…”

“…Nonetheless, there is no direct evidence to estimate the actual contribution of those brain areas to preparatory suppression of MEPs observed in the present study. Finally, preparatory suppression of MEPs can also be associated with subcortical and/or spinal levels of the motor system (Duque and Ivry 2009;Duque et al 2010;Fujiyama et al 2011;Hammond 2008, 2009;Tandonnet et al 2011).…”

Attention to baseline: does orienting visuospatial attention really facilitate target detection?

“…Alternatively, this effect may also be due to an early release of the proactive inhibitory control imposed by the mixed design: the presentation of the spatial cue may help release the inhibition of the superior colliculus on the ocular motoneurons that help to keep the eyes stationary on a visual target (Lo et al 2009). This hypothesis assumes, however, that proactive inhibitory control may be spatially selective (see Duque et al 2010 for an extended discussion about the selectivity of inhibitory mechanisms during response preparation). Such an interpretation is in line with studies suggesting that exogenous visuospatial attention specifically facilitates saccade planning rather than visual target processing (Khan et al 2010).…”

“…In particular, predictive cues elicit automatic motor activations, which, in turn, call for response inhibition to prevent false alarms, i.e., to withhold automatic responses to cues Sumner and Husain 2008; see also Allport 1993 for an early discussion). Such cue-related response inhibition probably involves multiple executive and motor mechanisms (Duque et al 2010;Stinear et al 2009;Van Der Lubbe et al 2005). Importantly, this inhibitory control relies not only on postcue responsive mechanisms but also on precue proactive mechanisms that depend on the subject's expectations of the trial structure (Jaffard et al 2007Boulinguez et al 2008Boulinguez et al , 2009Boy et al 2010;Chen et al 2010).…”

Foresight beats hindsight: The neural correlates underlying motor preparation in the pro‐/anti‐cue paradigm

“…Interestingly, the putamen was also more active in the long pro‐cue condition than in the long anti‐cue condition. One possible interpretation of this finding is that inhibition may also be necessary to prevent the premature execution of an already selected response, especially with longer preparation intervals (Duque, Lew, Mazzocchio, Olivier, & Ivry, 2010). …”