Comparison of Motor Inhibition in Variants of the Instructed-Delay Choice Reaction Time Task

Abstract

Using instructed-delay choice reaction time (RT) paradigms, many previous studies have shown that the motor system is transiently inhibited during response preparation: motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) over the primary motor cortex are typically suppressed during the delay period. This effect has been observed in both selected and non-selected effectors, although MEP changes in selected effectors have been more inconsistent across task versions. Here, we compared changes in MEP amplitudes in three different variants of an instructed-delay choice RT task. All variants required participants to choose between left and right index finger movements but the responses were either provided “in the air” (Variant 1), on a regular keyboard (Variant 2), or on a response device designed to control from premature responses (Variant 3). The task variants also differed according to the visual layout (more concrete in Variant 3) and depending on whether participants received a feedback of their performance (absent in Variant 1). Behavior was globally comparable between the three variants of the task although the propensity to respond prematurely was highest in Variant 2 and lowest in Variant 3. MEPs elicited in a non-selected hand were similarly suppressed in the three variants of the task. However, significant differences emerged when considering MEPs elicited in the selected hand: these MEPs were suppressed in Variants 1 and 3 whereas they were often facilitated in Variant 2, especially in the right dominant hand. In conclusion, MEPs elicited in selected muscles seem to be more sensitive to small variations to the task design than those recorded in non-selected effectors, probably because they reflect a complex combination of inhibitory and facilitatory influences on the motor output system. Finally, the use of a standard keyboard seems to be particularly inappropriate because it encourages participants to respond promptly with no means to control for premature responses, probably increasing the relative amount of facilitatory influences at the time motor inhibition is probed.

Effect of Aging on Motor Inhibition during Action Preparation under Sensory Conflict

“…Interestingly, the MEP data revealed that this behavioral gain was associated with a strengthened suppression of motor activity at the onset time of the imperative signal. That is, although MEPs were systematically suppressed at this time, as frequently reported in the past (Klein et al, 2012, 2016; Greenhouse et al, 2015b; Bestmann and Duque, 2016; Quoilin et al, 2016; Wilhelm et al, 2016), this effect was much stronger when conflict was expected than when it was not. Besides, we also found that, during actions selection, the motor representations were less affected by the presence of irrelevant distractors.…”

“…The optimal scalp position for eliciting an MEP in the left first dorsal interosseous muscle (FDI), so-called the hotspot, was identified and marked on a head cap fitted on the participant’s head to provide a reference landmark throughout the experimental session (Vandermeeren et al, 2009). We focused on a left hand muscle because the motor correlates of inhibitory control processes are thought to be more evident in the non-dominant compared to the dominant hand (Leocani et al, 2000; Duque et al, 2007; Quoilin et al, 2016; Wilhelm et al, 2016), but see also Klein et al (2016). The resting motor threshold (rMT) was determined at the hotspot as the minimal TMS intensity required to evoke MEPs of about 50 μV peak-to-peak in the relaxed FDI muscle in 5 out of 10 consecutive trials.…”

Physiological Markers of Motor Inhibition during Human Behavior

“…That is, MEPs probed following preparatory cues in a selected effector also become smaller relative to baseline. Moreover, this inhibition is often stronger than that observed when the same muscle is not selected for the forthcoming response [77, 84] (but see also [85, 86]), especially when probed at the end of the delay period (Fig. 3CD, right panel) [18].…”

“…4, lower leftward panel). However, inhibition is reliably observed in task-irrelevant muscle representations, either during a delay period [13, 86, 95, 96] or during a pre-movement period [78]. Thus, preparatory inhibition is not limited to non-selected effectors, but extends to task-irrelevant motor representations.…”

“…These findings, in combination with the consistent picture of inhibition in task-irrelevant muscles, present a major challenge to a model in which preparatory inhibition is assumed to result from reciprocal inhibitory interactions between alternative responses competing for selection. Rather, action preparation seems to entail a broadly-tuned inhibition of the motor output system, irrespective of the effector(s) involved in the action that is being prepared [13, 78, 86, 95]. …”