Planning face, hand, and leg movements: anatomical constraints on preparatory inhibition

Abstract

Motor-evoked potentials (MEPs), elicited by transcranial magnetic stimulation (TMS) over the motor cortex, are reduced during the preparatory period in delayed response tasks. In this study we examined how MEP suppression varies as a function of the anatomical organization of the motor cortex. MEPs were recorded from a left index muscle while participants prepared a hand or leg movement in experiment 1 or prepared an eye or mouth movement in experiment 2. In this manner, we assessed if the level of MEP suppression in a hand muscle varied as a function of the anatomical distance between the agonist for the forthcoming movement and the muscle targeted by TMS. MEP suppression was attenuated when the cued effector was anatomically distant from the hand (e.g., leg or facial movement compared with finger movement). A similar effect was observed in experiment 3 in which MEPs were recorded from a muscle in the leg and the forthcoming movement involved the upper limb or face. These results demonstrate an important constraint on preparatory inhibition: it is sufficiently broad to be manifest in a muscle that is not involved in the task, but it is not global, showing a marked attenuation when the agonist muscle belongs to a different segment of the body. NEW & NOTEWORTHY Using transcranial magnetic stimulation, we examined changes in corticospinal excitability as people prepared to move. Consistent with previous work, we observed a reduction in excitability during the preparatory period, an effect observed in both task-relevant and task-irrelevant muscles. However, this preparatory inhibition is anatomically constrained, attenuated in muscles belonging to a different body segment than the agonist of the forthcoming movement.

A TMS study of preparatory suppression in binge drinkers

“…Our findings in BDs clearly question this first reading of our data and emphasize the importance of considering task-irrelevant effectors to assess preparatory suppression. As such, the suppression effect is known to expand to various muscles within the moving limb, even if they are not involved in the task ( Labruna et al, 2019 ), as also supported by the current study. Moreover, irrelevant effectors are not (or little) influenced by facilitatory inputs that are mainly centered on the prime mover.…”

“…The resting motor threshold (rMT) was determined as the minimal TMS intensity required to evoke MEPs of at least 50 µV peak-to-peak in all 3 muscles for at least 5 out of 10 consecutive trials ( Derosiere et al, 2020 , Derosiere et al, 2019 , Duque et al, 2016 , Labruna et al, 2019 , Vassiliadis et al, 2019 ). In practice, most of the time it consisted in finding the rMT for the ADM, which was usually a bit higher than the rMT of the 2 other muscles.…”

“…Inhibitory control is particularly strong in stop-signal tasks where the successful suppression of actions following stop signals relies on a decrease in the excitability of the CS tract ( Duque et al, 2017 , Wessel et al, 2013 , Wessel and Aron, 2017 ). Interestingly, not only stopping but also preparing motor acts is associated with a robust CS suppression ( Duque et al, 2017 , Duque et al, 2012 , Duque et al, 2010 ), a phenomenon referred to as preparatory suppression (or inhibition) ( Derosiere, 2018 , Duque et al, 2017 , Greenhouse et al, 2015b , Hasbroucq et al, 1997 , Labruna et al, 2019 , Quoilin et al, 2019 , Vassiliadis et al, 2018 , Wilhelm et al,2017 ). An advantage of the latter measure of inhibitory control is that it is obtained in a context that is quite representative of everyday life (we continuously need to prepare actions and avoid selecting inappropriate ones) while stop-signal tasks are more artificial: most situations require inhibitory control to be internally generated, in the absence of explicit stop-signals.…”

Motor training strengthens corticospinal suppression during movement preparation

“…Preparatory suppression was present from the first blocks and was overall broad, concerning the prime-mover and task-irrelevant muscles, in both the selected and non-selected hands (Labruna et al, 2019). Most importantly, preparatory suppression became stronger over the course of practice and this effect concerned all the investigated effectors.…”

Considering Motor Excitability During Action Preparation in Gambling Disorder: A Transcranial Magnetic Stimulation Study

“…Accordingly, a drastic suppression of motor activity has been reported when subjects are in the process of stopping an action (6,7), but also during the preparation of motor acts (8,9). In particular, by measuring motor-evoked potentials (MEPs) elicited by single-pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (M1), studies have monitored changes in the excitability of the corticospinal pathway during instructed-delay choice reaction time (RT) tasks (10)(11)(12)(13)(14). Such tasks typically require participants to choose between responding with the left of the right hand according to an informative preparatory cue, and to withhold their response until the onset of an imperative signal.…”