Continuous theta-burst stimulation to the sensorimotor cortex affects contralateral gamma-aminobutyric acid level and resting-state networks

Lack of effects of eight-week left dorsolateral prefrontal theta burst stimulation on white matter macro/microstructure and connection in autism

Whether brain stimulation could modulate brain structure in autism remains unknown. This study explored the impact of continuous theta burst stimulation (cTBS) over the left dorsolateral prefrontal cortex (DLPFC) on white matter macro/microstructure in intellectually able children and emerging adults with autism. Sixty autistic participants were randomized (30 active) and received active or sham cTBS for eight weeks twice per week, 16 total sessions using a double-blind (participant-, rater-, analyst-blinded) design. All participants received high-angular resolution diffusion MR imaging at baseline and week 8. Twenty-eight participants in the active group and twenty-seven in the sham group with good imaging quality entered the final analysis. With longitudinal fixel-based analysis and network-based statistics, we found no significant difference between the active and sham groups in changes of white matter macro/microstructure and connections following cTBS. In addition, we found no association between baseline white matter macro/microstructure and autistic symptom changes from baseline to week 8 in the active group. In conclusion, we did not find a significant impact of left DLPFC cTBS on white matter macro/microstructure and connections in children and emerging adults with autism. These findings need to be interpreted in the context that the current intellectually able cohort in a single university hospital site limits the generalizability. Future studies are required to investigate if higher stimulation intensities and/or doses, other personal factors, or rTMS parameters might confer significant brain structural changes visible on MRI in ASD.

cTBS over primary motor cortex increased contralateral corticomuscular coupling and interhemispheric functional connection

Objective.Transcranial magnetic stimulation is a non-invasive brain stimulation technique that changes the activity of the cerebral cortex. Contralesional continuous theta burst stimulation (cTBS) has been proposed and verified beneficial to stroke motor recovery. However, the underlying mechanism is still unclear.Approach.20 healthy right-handed subjects were recruited in this study, receiving real-cTBS over their left primary motor cortex or sham-cTBS. We designed the finger tapping task (FTT) before and after stimulation and recorded the accuracy and reaction time (RT) of the task. The electroencephalogram and surface electromyogram signals were recorded during the left finger pinching task (FPT) before and after stimulation. We calculated cortico-muscular coherence (CMC) in the contralateral hemisphere and cortico-cortical coherence (CCC) in the bilateral hemisphere. The two-way repeated measures analysis of variance was used to analyze the effect of cTBS.Main results.In the FTT, there was a significant main effect of 'time' on RT (F(1, 38) = 24.739,p< 0.001). In the FPT, the results showed that there was a significant interaction effect on the CMC peak and area in the beta band (peak:F(1, 38) = 8.562,p= 0.006; area:F(1, 38) = 5.273,p= 0.027), on the CCC peak in the alpha band (F(1, 38) = 4.815,p= 0.034) and area in the beta band (F(1, 38) = 4.822,p= 0.034). The post hoc tests showed that the CMC peak (W= 20,p= 0.002), the CMC area (W= 13,p= 0.003) and the CCC peak (t= -2.696,p= 0.014) increased significantly after real-cTBS. However, there was no significant decrease or increase after sham-cTBS.Significance.Our study found that cTBS can improve CMC of contralateral hemisphere and CCC of bilateral hemisphere, indicating that cTBS can strengthen cortico-muscular and cortico-cortical coupling.

Quantitative GABA magnetic resonance spectroscopy as a measure of motor learning function in the motor cortex after subarachnoid hemorrhage

The neural mechanisms underlying gross and fine motor dysfunction after subarachnoid hemorrhage (SAH) remain unknown. The γ-aminobutyric acid (GABA) deficit hypothesis proposes that reduced neuronal GABA concentrations and the subsequent lack of GABA-mediated inhibition cause motor impairment after SAH. This study aimed to explore the correlation between GABA levels and a behavioral measure of motor performance in patients with SAH. Motor cortical GABA levels were assessed in 40 patients with SAH and 10 age-matched healthy controls using proton magnetic resonance spectroscopy. The GABA and N-acetylasparate (NAA) ratio was measured in the normal gray matter within the primary motor cortex. The relationship between GABA concentration and hand-motor performance was also evaluated. Results showed significantly lower GABA levels in patients with SAH's left motor cortex than in controls (GABA/NAA ratio: 0.282 ± 0.085 vs. 0.341 ± 0.031, respectively; p = 0.041). Reaction times (RTs), a behavioral measure of motor performance potentially dependent on GABAergic synaptic transmission, were significantly longer in patients than in controls (936.8 ± 303.8 vs. 440.2 ± 67.3 ms, respectively; p < 0.001). Moreover, motor cortical GABA levels and RTs exhibited a significant positive linear correlation among patients (r = 0.572, rs = 0.327, p = 0.0001). Therefore, a decrease in GABA levels in the primary motor cortex after SAH may lead to impaired cortical inhibition of neuronal function and indicates that GABA-mediated synaptic transmission in the motor cortex is critical for RT.

A systematic review of the neurobiological effects of theta-burst stimulation (TBS) as measured using functional magnetic resonance imaging (fMRI)

Theta burst stimulation (TBS) is associated with the modulation of a range of clinical, cognitive, and behavioural outcomes, but specific neurobiological effects remain somewhat unclear. This systematic literature review investigated resting-state and task-based functional magnetic resonance imaging (fMRI) outcomes post-TBS in healthy human adults. Fifty studies that applied either continuous-or intermittent-(c/i) TBS, and adopted a pretest-posttest or sham-controlled design, were included. For resting-state outcomes following stimulation applied to motor, temporal, parietal, occipital, or cerebellar regions, functional connectivity generally decreased in response to cTBS and increased in response to iTBS, though there were some exceptions to this pattern of response. These findings are mostly consistent with the assumed long-term depression (LTD)/long-term potentiation (LTP)-like plasticity effects of cTBS and iTBS, respectively. Task-related outcomes following TBS were more variable. TBS applied to the prefrontal cortex, irrespective of task or state, also produced more variable responses, with no consistent patterns emerging. Individual participant and methodological factors are likely to contribute to the variability in responses to TBS. Future studies assessing the effects of TBS via fMRI must account for factors known to affect the TBS outcomes, both at the level of individual participants and of research methodology.