Transcranial direct current stimulation on prefrontal and parietal areas enhances motor imagery

Effects of neurofeedback training combined with transcranial direct current stimulation on motor imagery: A randomized controlled trial

Introduction

Neurofeedback (NFB) training and transcranial direct current stimulation (tDCS) have been shown to individually improve motor imagery (MI) abilities. However, the effect of combining both of them with MI has not been verified. Therefore, the aim of this study was to examine the effect of applying tDCS directly before MI with NFB.

Methods

Participants were divided into an NFB group (n = 10) that performed MI with NFB and an NFB + tDCS group (n = 10) that received tDCS for 10 min before MI with NFB. Both groups performed 60 MI trials with NFB. The MI task was performed 20 times without NFB before and after training, and μ-event-related desynchronization (ERD) and vividness MI were evaluated.

Results

μ-ERD increased significantly in the NFB + tDCS group compared to the NFB group. MI vividness significantly increased before and after training.

Discussion

Transcranial direct current stimulation and NFB modulate different processes with respect to MI ability improvement; hence, their combination might further improve MI performance. The results of this study indicate that the combination of NFB and tDCS for MI is more effective in improving MI abilities than applying them individually.

Non-invasive brain stimulation in modulation of mental rotation ability: A systematic review and meta-analysis

Mental rotation, the ability to manipulate mental images, is an important function in human cognition. This systematic review and meta-analysis investigates the potential of non-invasive brain stimulation in modulation of this component of visuo-spatial perception. The PubMed database was reviewed prior to 31 September 2020 on randomized controlled trials investigating the effects of repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), and transcranial alternating current stimulation (tACS) on the mental rotation ability in healthy persons. A total of 17 studies (including 485 subjects) matched our inclusion criteria. Within their scope, overall, 46 sham-controlled experiments were performed. Methodology and results of each experiment are presented in a meta-analysis. The data show a large variety of methods and effects. The influence of (1) stimulation-technique (tDCS, tACS, and rTMS), (2) stimulation protocol (anodal, cathodal, bilateral tDCS, tACS, high-frequency rTMS, low-frequency rTMS, paired pulse rTMS, and theta burst stimulation), (3) stimulation timing (preconditioning and simultaneous), (4) stimulation location (left, right hemisphere, frontal, and parietal area), and (5) stimulus type (bodily and non-bodily) is discussed. The data indicate a beneficial effect of anodal tDCS and of tACS and no effect of cathodal tDCS on the mental rotation ability. Bilateral tDCS protocols both improved and worsened the parameters assessed. The small effect sizes obtained in mostly rTMS experiments require cautious interpretation.

Effect of transcranial direct current stimulation on the psychomotor, cognitive, and motor performances of power athletes

In sports science, transcranial direct current stimulation (tDCS) has many unknown effects on neuromuscular, psychomotor and cognitive aspects. Particularly, its impact on power performances remains poorly investigated. Eighteen healthy young males, all trained in a jumping sport (parkour) performed three experimental sessions: anodal tDCS applied either on the left dorsolateral prefrontal cortex (dlPFC, cathode in supraorbital area) or on the primary motor cortex (M1, cathode on contralateral shoulder), and a placebo condition (SHAM), each applied for 20 min at 2 mA. Pre and post, maximal vertical and horizontal jumps were performed, associated to leg neuromuscular assessment through electromyography and peripheral nerve stimulations. Actual and imagined pointing tasks were also performed to evaluate fine motor skills, and a full battery of cognitive and psychomotor tests was administered. M1 tDCS improved jump performance accompanied by an increase in supraspinal and spinal excitabilities. dlPFC stimulation only impacted the pointing tasks. No effect on cognitive tests was found for any of the tDCS conditions. To conclude, the type of performance (maximal versus accurate) affected depended upon the tDCS montage. Finally, athletes responded well to tDCS for motor performance while results to cognitive tests seemed unaffected, at least when implemented with the present rationale.

Influence of iTBS on the Acute Neuroplastic Change After BCI Training

Objective: Brain-computer interface (BCI) training is becoming increasingly popular in neurorehabilitation. However, around one third subjects have difficulties in controlling BCI devices effectively, which limits the application of BCI training. Furthermore, the effectiveness of BCI training is not satisfactory in stroke rehabilitation. Intermittent theta burst stimulation (iTBS) is a powerful neural modulatory approach with strong facilitatory effects. Here, we investigated whether iTBS would improve BCI accuracy and boost the neuroplastic changes induced by BCI training. Methods: Eight right-handed healthy subjects (four males, age: 20-24) participated in this two-session study (BCI-only session and iTBS+BCI session in random order). Neuroplastic changes were measured by functional near-infrared spectroscopy (fNIRS) and single-pulse transcranial magnetic stimulation (TMS). In BCI-only session, fNIRS was measured at baseline and immediately after BCI training. In iTBS+BCI session, BCI training was followed by iTBS delivered on the right primary motor cortex (M1). Single-pulse TMS was measured at baseline and immediately after iTBS. fNIRS was measured at baseline, immediately after iTBS, and immediately after BCI training. Paired-sample t-tests were used to compare amplitudes of motor-evoked potentials, cortical silent period duration, oxygenated hemoglobin (HbO2) concentration and functional connectivity across time points, and BCI accuracy between sessions. Results: No significant difference in BCI accuracy was detected between sessions (p > 0.05). In BCI-only session, functional connectivity matrices between motor cortex and prefrontal cortex were significantly increased after BCI training (p's < 0.05). In iTBS+BCI session, amplitudes of motor-evoked potentials were significantly increased after iTBS (p's < 0.05), but no change in HbO2 concentration or functional connectivity was observed throughout the whole session (p's > 0.05). Conclusions: To our knowledge, this is the first study that investigated how iTBS targeted on M1 influences BCI accuracy and the acute neuroplastic changes after BCI training. Our results revealed that iTBS targeted on M1 did not influence BCI accuracy or facilitate the neuroplastic changes after BCI training. Therefore, M1 might not be an effective stimulation target of iTBS for the purpose of improving BCI accuracy or facilitate its effectiveness; other brain regions (i.e., prefrontal cortex) are needed to be further investigated as potentially effective stimulation targets.

Anodal transcranial direct current stimulation over the posterior parietal cortex enhances three-dimensional mental rotation ability

Prior neuroimaging and neurophysiological studies have found that the right posterior parietal cortex (PPC) plays an important role in mental rotation ability. Transcranial direct-current stimulation (tDCS) has been shown the potential to enhance cognitive ability by delivering a low current to the brain cortex of interest, via electrodes on the scalp. Here, we tested whether stimulating the PPC with tDCS can improve three-dimensional mental rotation performance and narrow gender difference. The classic three-dimensional Shepard-Metzler task was measured after three stimulation conditions (right PPC, left PPC, sham stimulation). The results indicated that stimulating the right PPC induced an improvement in accuracy and response time of mental rotation relative to sham stimulation. Stimulating the left PPC caused an enhancement in the accuracy but not in the response time. Gender difference during mental rotation was diminished after stimulation. These findings indicated that the PPC regions played a causal role in mental rotation ability. tDCS could be used as a promising non-invasive method to improve mental rotation skills in individuals with lower ability and to provide an effective therapeutic tool for neurological disorder rehabilitation.