Challenging the function of motor inhibition: Does it really assist action selection?

Abstract

By applying transcranial magnetic stimulation (TMS) over the primary motor cortex (M1) to elicit motor-evoked potentials (MEPs) in muscles of the contralateral hand during reaction time (RT) tasks, many studies have reported a strong suppression of MEPs during action preparation, a phenomenon called preparatory inhibition. Several hypotheses have been put forward regarding the role of this inhibition, with the predominant view suggesting that it would help action selection. However, this assumption is still a matter of debate. Here, we aimed at directly addressing this idea by comparing MEPs in a task that required subjects to select a finger response within a set of predefined options (choice RT task: left or right index finger abduction) or when subjects simply had to provide the same finger response on every trial, in the absence of choice (simple RT task). Moreover, we minimized any effect that could be associated with other forms of inhibition. In both versions of the task, TMS was applied on both M1 (double-coil protocol) at several time points between the go signal and the left or right index finger response, eliciting MEPs bilaterally in the prime mover (index finger agonist) and in an irrelevant muscle (pinky agonist). Overall, MEP suppression was moderate in this study; it was only found for the irrelevant muscle. As such, MEPs in the index agonist were facilitated when elicited in a responding hand (e.g. left MEPs preceding left responses) and remained mostly unchanged in a non-responding hand (e.g. left MEPs preceding right responses). In contrast, MEPs were almost always suppressed in the pinky muscle when elicited in the non-responding hand and sometimes also in the responding hand. Importantly, this effect was more consistent in the choice than in the simple RT task, supporting the view that preparatory inhibition may assist action selection. Moreover, the fact that it sometimes concerned the responding hand is coherent with the idea of a global process, suppressing broadly the motor system.

Motor training strengthens corticospinal suppression during movement preparation

“…This was expected given that the TMS ‘hotspot’ was determined based on MEPs elicited in the FDI and not the ADM (see Methods section). Still, past studies indicate that this method can provide us with a reliable measure of CS excitability changes occurring in a task-irrelevant effector (Vassiliadis et al, 2018; Quoilin et al, 2019). As evident on Fig.…”

“…It also provided us with a very precise measure of the RTs (precision = 1 ms), while controlling for the initial position of the index fingers. This set-up has been used in previously published work (Quoilin et al, 2016, 2018, 2019; Grandjean et al, 2019).…”

“…, double-coil TMS) eliciting MEPs in one or in both hands, respectively. Importantly, in double-coil trials, a 1-ms interval separated the onset of the two pulses, eliciting MEPs in both hands at a near simultaneous time (Algoet et al, 2018; Grandjean et al, 2018; Vassiliadis et al, 2018; Quoilin et al, 2019). This interval was used to avoid direct electromagnetic interference between the two coils (Cincotta et al, 2005), while preventing transcallosal interactions that would occur between motor areas with longer delays (Ferbert et al, 1992; Hanajima et al, 2001).…”

Experimental and Theoretical Study to Increase the Solar-Organic Rankin Cycle Efficiency

“…12,13 There is a continuous increase in research activity related to ORC energy systems in the past years, which has proven the value of this technology and its ability to improve energy sustainability. 14,15 It was concluded that the maximum efficiency increases with increasing the evaporation temperature and the extraction number, however, it decreases by increasing the superheat temperature, since the work of the turbine grows by increasing evaporation rate and superheat temperatures but decreases with increasing the extraction rates. Organic Rankine cycle (ORC) as a power generation method from medium and low thermal grade heat sources is currently a strong player in the market.…”

Experimental and Theoretical Study to Increase the Solar-Organic Rankine Cycle Efficiency

“…12,13 There is a continuous increase in research activity related to ORC energy systems in the past years, which has proven the value of this technology and its ability to improve energy sustainability. 14,15 It was concluded that the maximum efficiency increases with increasing the evaporation temperature and the extraction number, however, it decreases by increasing the superheat temperature, since the work of the turbine grows by increasing evaporation rate and superheat temperatures but decreases with increasing the extraction rates. Organic Rankine cycle (ORC) as a power generation method from medium and low thermal grade heat sources is currently a strong player in the market.…”