Premovement suppression of corticospinal excitability may be a necessary part of movement preparation

Abstract

In a warned reaction time (RT) task, corticospinal excitability (CSE) decreases in taskrelated muscles at the time of the imperative signal (preparatory inhibition). Because RT tasks emphasise speed of response, it is impossible to distinguish whether preparatory inhibition reflects a mechanism preventing premature reactions, or whether it is an inherent part of movement preparation. We used transcranial magnetic stimulation (TMS) to study CSE changes preceding RT movements and movements that were either selfpaced (SP) or performed at predictable times to coincide with an external event (PT).Results show that CSE changes over a similar temporal profile in all cases, suggesting that preparatory inhibition is a necessary state in planned movements allowing the transition between rest and movement. Additionally, TMS given shortly before the times to move speeded the onset of movements in both RT and SP contexts, suggesting that their initiation depends on a form of trigger that can be conditioned by external signals.On the contrary, PT movements do not show this effect, suggesting the use of a mechanistically different triggering strategy. This relative immunity of PT tasks to be biased by external events may reflect a mechanism that ensures priority of internal predictive signals to trigger movement onset.

SICI during changing brain states: Differences in methodology can lead to different conclusions

“…Finally, single-pulse TMS using 1mV WS intensity at RT-200 resulted in significantly smaller MEP amplitudes than at WS (t ¼ 3.916, p ¼ 0.001), confirming that corticospinal excitability decreased during movement preparation (Fig. 1D) [16].…”

Premovement inhibition can protect motor actions from interference by response‐irrelevant sensory stimulation

“…The results we present here, and previous findings that preparatory inhibition is present before self‐timed movements (Ibáñez et al . 2020), are then inconsistent with the impulse control hypothesis (Duque & Ivry, 2009; Duque et al . 2010).…”

“…2011; Ibáñez et al . 2020). There are three main explanations which have been put forward regarding the role of this suppression of motor circuits before movement onset.…”

“…2018), and CS suppression is observed in self‐timed actions which do not rely on initiation taking place at a particular time (Ibáñez et al . 2020), findings of which are incompatible with preparatory inhibition acting to prevent premature initiation. Finally, the spotlight account is incompatible with the observation of CS suppression in non‐selected muscles – it could be argued that this would be maladaptive in that it may lead to an increased risk of unintentionally triggering task‐irrelevant actions.…”

Dissecting two distinct interneuronal networks in M1 with transcranial magnetic stimulation

“…The first TMS experiment applied in this context showed that cortical excitability is reduced during movement preparation (Hasbrouq et al 1997 ). While this was initially interpreted as an inhibitory signal that helps to prevent actions from being executed prematurely (Duque and Ivry 2009 ), the preparatory suppression effect is still a matter of debate (Ibáñez et al 2019b ).…”