Individual differences in intracortical inhibition predict motor-inhibitory performance.

Studies in which single- and paired-pulse TMS was applied during motor task performance have shed considerable light on the functional relevance of popular TMS-derived neurophysiological biomarkers such as short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI). While it has become well established that corticospinal excitability and intracortical inhibition are modulated during the enactment and cancellation of actions, it has remained unclear as to whether interindividual differences in these neurophysiological markers were associated with an individual's actual ability to restrain and cancel actions. In this study, we found that individual differences in both SICI and LICI were positively associated with relevant performance metrics on the go/no-go task and stop-signal task. Specifically, we found that individuals with greater resting SICI and LICI were faster to respond on go trials of the go/no-go task and were also more accurate at inhibiting their manual responses on both go/no-go and stop-signal tasks. These results are in support of findings from our earlier study and also provide new evidence for a general relationship between individual differences in resting-state GABAergic intracortical inhibitory functioning and motor inhibition.

Impaired motor inhibition in developmental coordination disorder.

This study aimed to evaluate the 'inhibitory deficit' hypothesis of developmental coordination disorder (DCD). We adopted a multifaceted approach, investigating two distinct, yet complimentary facets of motor inhibition: action restraint and action cancellation. This was achieved using carefully constructed versions of the 'Go/No-go' and 'Stop-signal' tasks, respectively. The sample comprised 11 young adults with DCD aged between 18 and 30 years of age and 11 typically developing, age-matched controls. Participants completed both the 'Go/No-go' and 'Stop-signal' tasks to assess action restraint and action cancellation respectively. Individuals with DCD were less efficient than their typically developing peers at performing both action restraint and action cancellation, indicated by significantly reduced action restraint efficiency index scores on the 'Go/No-go' task and a trend towards longer stop-signal reaction times on the 'Stop-signal' task. This work clarifies disparate evidence speaking to the integrity of action restraint in DCD and provides the first account of action cancellation in DCD using a purpose-built measure. In support of the inhibitory deficit hypothesis of DCD, our results suggest that young adults with DCD experience broad difficulties with engaging inhibitory mechanisms during motor behaviour.

Corticospinal excitability during motor imagery is reduced in young adults with developmental coordination disorder.

While a compelling body of behavioral research suggests that individuals with developmental coordination disorder (DCD) experience difficulties engaging motor imagery (MI), very little is known about the neural correlates of this deficit. Since corticospinal excitability is a predictor of MI proficiency in healthy adults, we reasoned that decreased MI efficiency in DCD may be paralleled by atypical primary motor cortex (PMC) activity. Participants were 29 young adults aged 18- 36 years: 8 with DCD (DCD) and 21 controls. Six participants with DCD and 15 controls showed behavioral profiles consistent with the use of a MI strategy (MI users) while performing a novel adaptation of the classic hand laterality task (HLT). Single-pulse transcranial magnetic stimulation (TMS) was administered to the hand node of the left PMC (hPMC) at 50ms, 400ms or 650ms post stimulus presentation during the HLT. Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) via electromyography. As predicted, MI users with DCD were significantly less efficient than MI using controls, shown by poorer performance on the HLT. Importantly, unlike healthy controls, no evidence of enhanced hPMC activity during MI was detected in our DCD group. Our data are consistent with the view that inefficient MI in DCD may be subserved by decreased hPMC activity. These findings are an important step towards clarifying the neuro-cognitive correlates of poor MI ability and motor skill in individuals with DCD.