The role of the primary motor cortex in motor imagery: A theta burst stimulation study.

While mentally simulated actions activate similar neural structures to overt movement, the role of the primary motor cortex (PMC) in motor imagery remains disputed. The aim of the study was to use continuous theta burst stimulation (cTBS) to modulate corticospinal activity to investigate the putative role of the PMC in implicit motor imagery in young adults with typical and atypical motor ability. A randomized, double blind, sham-controlled, crossover, offline cTBS protocol was applied to 35 young adults. During three separate sessions, adults with typical and low motor ability (developmental coordination disorder [DCD]), received active cTBS to the PMC and supplementary motor area (SMA), and sham stimulation to either the PMC or SMA. Following stimulation, participants completed measures of motor imagery (i.e., hand rotation task) and visual imagery (i.e., letter number rotation task). Although active cTBS significantly reduced corticospinal excitability in adults with typical motor ability, neither task performance was altered following active cTBS to the PMC or SMA, compared to performance after sham cTBS. These results did not differ across motor status (i.e., typical motor ability and DCD). These findings are not consistent with our hypothesis that the PMC (and SMA) is directly involved in motor imagery. Instead, previous motor cortical activation observed during motor imagery may be an epiphenomenon of other neurophysiological processes and/or activity within brain regions involved in motor imagery. This study highlights the need to consider multi-session theta burst stimulation application and its neural effects when probing the putative role of motor cortices in motor imagery.

Frequency and Intensity of Premonitory Urges-to-Tic in Tourette Syndrome Is Associated With Supplementary Motor Area GABA+ Levels.

BACKGROUND: Individuals with Tourette syndrome (TS) often report that they express tics as a means of alleviating the experience of unpleasant sensations. These sensations are perceived as an urge to act and are referred to as premonitory urges. Premonitory urges have been the focus of recent efforts to develop interventions to reduce tic expression in those with TS. OBJECTIVE: The aim of this study was to examine the contribution of brain γ-aminobutyric acid (GABA) and glutamate levels of the right primary sensorimotor cortex (SM1), supplementary motor area (SMA), and insular cortex (insula) to tic and urge severity in children with TS. METHODS: Edited magnetic resonance spectroscopy was used to assess GABA+ (GABA + macromolecules) and Glx (glutamate + glutamine) of the right SM1, SMA, and insula in 68 children with TS (MAge = 10.59, SDAge = 1.33) and 41 typically developing control subjects (MAge = 10.26, SDAge = 2.21). We first compared GABA+ and Glx levels of these brain regions between groups. We then explored the association between regional GABA+ and Glx levels with urge and tic severity. RESULTS: GABA+ and Glx of the right SM1, SMA, and insula were comparable between the children with TS and typically developing control subjects. In children with TS, lower levels of SMA GABA+ were associated with more severe and more frequent premonitory urges. Neither GABA+ nor Glx levels were associated with tic severity. CONCLUSIONS: These results broadly support the role of GABAergic neurotransmission within the SMA in the experience of premonitory urges in children with TS. © 2021 International Parkinson and Movement Disorder Society.

Mental rotation performance in young adults with and without developmental coordination disorder.

While there have been consistent behavioural reports of atypical hand rotation task (HRT) performance in adults with developmental coordination disorder (DCD), this study aimed to clarify whether this deficit could be attributed to specific difficulties in motor imagery (MI), as opposed to broad deficits in general mental rotation. Participants were 57 young adults aged 18-30 years with (n = 22) and without DCD (n = 35). Participants were compared on the HRT, a measure of MI, and the letter number rotation task (LNRT), a common visual imagery task. Only participants whose behavioural performance on the HRT suggested use of a MI strategy were included in group comparisons. Young adults with DCD were significantly less efficient compared to controls when completing the HRT yet showed comparable performance on the LNRT relative to adults with typical motor ability. Our data are consistent with the view that atypical HRT performance in adults with DCD is likely to be attributed to specific difficulties engaging in MI, as opposed to deficits in general mental rotation. Based on the theory that MI provides insight into the integrity of internal action representations, these findings offer further support for the internal modelling deficit hypothesis of DCD.