Effects of High-Definition Anodal Transcranial Direct Current Stimulation Applied Simultaneously to Both Primary Motor Cortices on Bimanual Sensorimotor Performance

Application of bilateral tDCS over left and right M1 produces asymmetric training and retention effects when learning a rhythmic bimanual task

Many motor skills require precise coordination between the arms to accomplish. The use of transcranial direct current stimulation (tDCS) has helped to reveal hemispheric contributions to bimanual skills. In this study, three bilateral montages were used to explore hemispheric contributions to a rhythmic bimanual skill: anode left M1/cathode right M1 (LARC), anode right M1/cathode left M1 (RALC), and sham. Stimulation lasted 20-minutes during training. Retention was examined 6-hr after training. Participants (n = 46) learned a bimanual 90° relative-phase pattern with a half-cycle movement amplitude goal of 12 cm per arm at self-selected movement frequencies. Greater coordination variability in the 90° pattern emerged early under RALC compared to LARC, with no difference in performance accuracy. Larger movement amplitudes emerged in training with LARC compared to sham but not compared to RALC. tDCS montage had no impact on coordination variability and accuracy of the 90° pattern after the 6-hr delay. Montage was associated with a delayed movement amplitude effect emerging in retention, with larger amplitudes in LARC compared to RALC and sham. The asymmetries observed across training and retention emerged from of an interaction between tDCS and the left-hemisphere's role in the control of bimanual movements in right-handed individuals.

The effects of bilateral M1 anodal tDCS on corticomotor excitability and acquisition the of a bimanual videogame skill

Most activities of daily life involve some degree of coordinated, bimanual activity from the upper limbs. However, compared to single-handed movements, bimanual movements are processed, learned, and controlled from both hemispheres of the brain. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that enhances motor learning by modulating the activity of movement-associated brain regions. While effective in simple, single-handed tasks, tDCS has shown mixed results in complex bimanual tasks. This study investigated the effects of bilateral M1 anodal tDCS (biM1 a-tDCS) on learning and cortical excitability during a customized, bimanual racing videogame task. Thirty-six right-handed adults completed three lab visits (∼48 h apart), practicing the task while receiving either biM1 a-tDCS or SHAM tDCS. Cortical excitability was measured with transcranial magnetic stimulation (TMS) and electromyography (EMG) before and after the first visit. Though all subjects demonstrated improvements over the course of the study, our analyses revealed significantly faster rates of learning on days 1 & 2, but not day 3, of practice in subjects receiving biM1 a-tDCS. Moreover, perhaps due to differences in baseline gaming experience and aptitude, this effect appeared to be stronger in female subjects. Interestingly, no significant differences in corticomotor excitability were observed between conditions. Though biM1 a-tDCS did not appear to impact corticomotor excitability, our results contribute to the growing body of evidence which seems to suggest that multifocal tDCS protocols may be superior to traditional, single-site tDCS for the enhancement of bimanual motor learning.

Effects of transcranial direct current stimulation combined with Bosu ball training on the injury potential during drop landing in people with chronic ankle instability

Purpose

To investigate the effects of transcranial direct current stimulation (tDCS) combined with Bosu ball training on the injury potential during drop landing in people with chronic ankle instability (CAI).

Methods

A total of 40 participants with CAI were recruited and randomly divided into the tDCS + Bosu and Bosu groups. The people in the tDCS + Bosu group received intervention of tDCS combined with Bosu ball training, and those in the Bosu group received intervention of sham tDCS and Bosu ball training, for 6 weeks with three 20-min sessions per week. Before (week0) and after (week7) the intervention, all participants drop-landed on a trap-door device, with their affected limbs on a moveable platform, which could be flipped 24° inward and 15° forward to mimic an ankle inversion condition. The kinematic data were captured using a twelve-camera motion capture system. Two-way ANOVA with repeated measures was used to analyze data.

Results

Significant group-by-intervention interactions were detected in the peak ankle inversion angular velocity (p = 0.047, η2 p = 0.118), the time to peak ankle inversion (p = 0.030, η2 p = 0.139), and the plantarflexion angle at the moment of peak ankle inversion (p = 0.014, η2 p = 0.173). Post hoc comparisons showed that compared with week0, the peak ankle inversion angular velocity and the plantarflexion angle at the moment of peak ankle inversion were reduced, the time to peak ankle inversion was advanced in both groups at week7, and the changes were greater in the tDCS + Bosu group compared to the Bosu group. And, a significant intervention main effect was detected in the peak ankle inversion angle in the two groups (p < 0.001, η2 p = 0.337).

Conclusion

Compared with the Bosu ball training, the tDCS combined with Bosu ball training was more effective in reducing the injury potential during drop landing in people with CAI.

Simultaneous high-definition transcranial direct current stimulation and robot-assisted gait training in stroke patients

This study investigates whether simultaneous high-definition transcranial direct current stimulation (HD-tDCS) enhances the effects of robot-assisted gait training in stroke patients. Twenty-four participants were randomly allocated to either the robot-assisted gait training with real HD-tDCS group (real HD-tDCS group) or robot-assisted gait training with sham HD-tDCS group (sham HD-tDCS group). Over four weeks, both groups completed 10 sessions. The 10 Meter Walk Test, Timed Up and Go, Functional Ambulation Category, Functional Reach Test, Berg Balance Scale, Dynamic Gait Index, Fugl-Meyer Assessment, and Korean version of the Modified Barthel Index were conducted before, immediately after, and one month after the intervention. The real HD-tDCS group showed significant improvements in the 10 Meter Walk Test, Timed Up and Go, Functional Reach Test, and Berg Balance Scale immediately and one month after the intervention, compared with before the intervention. Significant improvements in the Dynamic Gait Index and Fugl-Meyer Assessment were also observed immediately after the intervention. The sham HD-tDCS group showed no significant improvements in any of the tests. Application of HD-tDCS during robot-assisted gait training has a positive effect on gait and physical function in chronic stroke patients, ensuring long-term training effects. Our results suggest the effectiveness of HD-tDCS as a complementary tool to enhance robotic gait rehabilitation therapy in chronic stroke patients.

Motor learning and tDCS: A systematic review on the dependency of the stimulation effect on motor task characteristics or tDCS assembly specifications

TDCS is one of the most commonly used methods among studies with transcranial electrical stimulation and motor skills learning. Differences between study results suggest that the effect of tDCS on motor learning is dependent on the motor task performed or on the tDCS assembly specification used in the learning process. This systematic review aimed to analyze the tDCS effect on motor learning and verify whether this effect is dependent on the task or tDCS assembly specifications. Searches were performed in PubMed, SciELO, LILACS, Web of Science, CINAHL, Scopus, SPORTDiscus, Cochrane Central Register of Controlled Trials (CENTRAL), Embase, and PsycINFO. Articles were included that analyzed the effect of tDCS on motor learning through pre-practice, post-practice, retention, and/or transfer tests (period ≥24 h). The tDCS was most frequently applied to the primary motor cortex (M1) or the cerebellar cortex (CC) and the majority of studies found significant stimulation effects. Studies that analyzed identical or similar motor tasks show divergent results for the tDCS effect, even when the assembly specifications are the same. The tDCS effect is not dependent on motor task characteristics or tDCS assembly specifications alone but is dependent on the interaction between these factors. This interaction occurs between uni and bimanual tasks with anodal uni and bihemispheric (bilateral) stimulations at M1 or with anodal unihemispheric stimulations (unilateral and centrally) at CC, and between tasks of greater or lesser difficulty with single or multiple tDCS sessions. Movement time seems to be more sensitive than errors to indicate the effects of tDCS on motor learning, and a sufficient amount of motor practice to reach the "learning plateau" also seems to determine the effect of tDCS on motor learning.

Bimanual motor skill learning after stroke: Combining robotics and anodal tDCS over the undamaged hemisphere: An exploratory study

Background

Since a stroke can impair bimanual activities, enhancing bimanual cooperation through motor skill learning may improve neurorehabilitation. Therefore, robotics and neuromodulation with transcranial direct current stimulation (tDCS) are promising approaches. To date, tDCS has failed to enhance bimanual motor control after stroke possibly because it was not integrating the hypothesis that the undamaged hemisphere becomes the major poststroke hub for bimanual control.

Objective

We tested the following hypotheses: (I) In patients with chronic hemiparetic stroke training on a robotic device, anodal tDCS applied over the primary motor cortex of the undamaged hemisphere enhances bimanual motor skill learning compared to sham tDCS. (II) The severity of impairment correlates with the effect of tDCS on bimanual motor skill learning. (III) Bimanual motor skill learning is less efficient in patients than in healthy individuals (HI).

Methods

A total of 17 patients with chronic hemiparetic stroke and 7 healthy individuals learned a complex bimanual cooperation skill on the REAplan® neurorehabilitation robot. The bimanual speed/accuracy trade-off (biSAT), bimanual coordination (biCo), and bimanual force (biFOP) scores were computed for each performance. In patients, real/sham tDCS was applied in a crossover, randomized, double-blind approach.

Results

Compared to sham, real tDCS did not enhance bimanual motor skill learning, retention, or generalization in patients, and no correlation with impairment was noted. The healthy individuals performed better than patients on bimanual motor skill learning, but generalization was similar in both groups.

Conclusion

A short motor skill learning session with a robotic device resulted in the retention and generalization of a complex skill involving bimanual cooperation. The tDCS strategy that would best enhance bimanual motor skill learning after stroke remains unknown.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT02308852, identifier: NCT02308852.

Modulation of Interhemispheric Synchronization and Cortical Activity in Healthy Subjects by High-Definition Theta-Burst Electrical Stimulation

Background

Various forms of theta-burst stimulation (TBS) such as intermittent TBS (iTBS) and continuous TBS (cTBS) have been introduced as novel facilitation/suppression schemes during repetitive transcranial magnetic stimulation (rTMS), demonstrating a better efficacy than conventional paradigms. Herein, we extended the rTMS-TBS schemes to electrical stimulation of high-definition montage (HD-TBS) and investigated its neural effects on the human brain.

Methods

In a within-subject design, fifteen right-handed healthy adults randomly participated in 10 min and 2 mA HD-TBS sessions: unilateral (Uni)-iTBS, bilateral (Bi)-cTBS/iTBS, and sham stimulation over primary motor cortex regions. A 20-channel near-infrared spectroscopy (NIRS) system was covered on the bilateral prefrontal cortex (PFC), sensory motor cortex (SMC), and parietal lobe (PL) for observing cerebral hemodynamic responses in the resting-state and during fast finger-tapping tasks at pre-, during, and poststimulation. Interhemispheric correlation coefficient (IHCC) and wavelet phase coherence (WPCO) from resting-state NIRS and concentration of oxyhemoglobin during fast finger-tapping tasks were explored to reflect the symmetry between the two hemispheres and cortical activity, respectively.

Results

The IHCC and WPCO of NIRS data in the SMC region under Bi-cTBS/iTBS showed relatively small values at low-frequency bands III (0.06–0.15 Hz) and IV (0.02–0.06), indicating a significant desynchronization in both time and frequency domains. In addition, the SMC activation induced by fast finger-tapping exercise was significantly greater during Uni-iTBS as well as during and post Bi-cTBS/iTBS sessions.

Conclusions

It appears that a 10 min and 2 mA Bi-cTBS/iTBS applied over two hemispheres within the primary motor cortex region could effectively modulate the interhemispheric synchronization and cortical activation in the SMC of healthy subjects. Our study demonstrated that bilateral HD-TBS approaches is an effective noninvasive brain stimulation scheme which could be a novel therapeutic for inducing effects of neuromodulation on various neurological disorders caused by ischemic stroke or traumatic brain injuries.

Gamma-transcranial alternating current stimulation on the cerebellum and supplementary motor area improves bimanual motor skill

BACKGROUND

Bimanual movements require sophisticated coordination of both hands. For improving bimanual motor skills, previous studies employed non-invasive brain stimulation methods to evaluate their effects on symmetrical and/or gross bimanual motor skills. However, asymmetrical and elaborate movements were not sufficiently improved. Studies using non-invasive brain stimulation have examined the effects of stimulation on the primary and supplementary motor areas (SMA),) but not on the cerebellar regions.

OBJECTIVE

We investigated whether the transcranial alternating current stimulation (tACS), which modulates oscillations in the cerebral cortex, of the cerebellum and SMA improves bimanual movements.

METHODS

Bimanual movements were assessed in 22 healthy young adults (mean age: 21.3 ± 1.5 years) via 13 trials of the Purdue Pegboard Test (PPT). A DC stimulator delivered 70Hz tACS (γ-tACS) at 1mA intensity via electrodes placed over the SMA, cerebellum and left shoulder in 5s fade in/out cycles of 5s for a total stimulus duration of 60s for in each trial. Four stimulation conditions were applied and compared for statistical differences.

RESULTS

The γ-tACS of the cerebellum, γ-tACS of the SMA and simultaneous stimulation of both regions caused significant improvement in PPT performance scores. The γ-tACS of the cerebellum improved PPT performance in all subjects and was more effective than the γ-tACS of the SMA.

CONCLUSION

The γ-tACS of the cerebellum effectively and reliably improves complex bimanual motor skills. Although the neural mechanisms of the stimulation effect remain unclear, these results can guide the future development of new stimulation methods for improving bimanual motor skills.

Noninvasive neuromodulation and rehabilitation to promote functional restoration in persons with spinal cord injury

PURPOSE OF REVIEW

This review will focus on the use of clinically accessible neuromodulatory approaches for functional restoration in persons with spinal cord injury (SCI).

RECENT FINDINGS

Functional restoration is a primary rehabilitation priority for individuals with SCI. High-tech neuromodulatory modalities have been used in laboratory settings to improve hand and walking function as well as to reduce spasticity and pain in persons with SCI. However, the cost, limited accessibility, and required expertise are prohibitive for clinical applicability of these high-tech modalities. Recent literature indicates that noninvasive and clinically accessible approaches targeting supraspinal, spinal, and peripheral neural structures can modulate neural excitability. Although a limited number of studies have examined the use of these approaches for functional restoration and amelioration of secondary complications in SCI, early evidence investigating their efficacy when combined with training is encouraging.

SUMMARY

Larger sample studies addressing both biomarker identification and dosing are crucial next steps in the field of neurorehabilitation research before novel noninvasive stimulation approaches can be incorporated into standard clinical practice.

Neuromodulatory effects of HD-tACS/tDCS on the prefrontal cortex: A resting-state fNIRS-EEG study

Transcranial direct and alternating current stimulation (tDCS and tACS, respectively) can modulate human brain dynamics and cognition. However, these modalities have not been compared using multiple imaging techniques concurrently. In this study, 15 participants participated in an experiment involving two sessions with a gap of 10 d. In the first and second sessions, tACS and tDCS were administered to the participants. The anode for tDCS was positioned at point FpZ, and four cathodes were positioned over the left and right prefrontal cortices (PFCs) to target the frontal regions simultaneously. tDCS was administered with 1 mA current. tACS was supplied with a current of 1 mA (zero-to-peak value) at 10 Hz frequency. Stimulation was applied concomitantly with functional near-infrared spectroscopy and electroencephalography acquisitions in the resting-state. The statistical test showed significant alteration (p < 0.001) in the mean hemodynamic responses during and after tDCS and tACS periods. Between-group comparison revealed a significantly less (p < 0.001) change in the mean hemodynamic response caused by tACS compared with tDCS. As hypothesized, we successfully increased the hemodynamics in both left and right PFCs using tDCS and tACS. Moreover, a significant increase in alpha-band power (p < 0.01) and low beta band power (p < 0.05) due to tACS was observed after the stimulation period. Although tDCS is not frequency-specific, it increased but not significantly (p > 0.05) the powers of most bands including delta, theta, alpha, low beta, high beta, and gamma. These findings suggest that both hemispheres can be targeted and that both tACS and tDCS are equally effective in high-definition configurations, which may be of clinical relevance.

Effects of Transcranial Direct Current Stimulation and High-Definition Transcranial Direct Current Stimulation Enhanced Motor Learning on Robotic Transcranial Magnetic Stimulation Motor Maps in Children

Introduction: Conventional transcranial direct current stimulation (tDCS) and high-definition tDCS (HD-tDCS) may improve motor learning in children. Mechanisms are not understood. Neuronavigated robotic transcranial magnetic stimulation (TMS) can produce individualised maps of primary motor cortex (M1) topography. We aimed to determine the effects of tDCS- and HD-tDCS-enhanced motor learning on motor maps. Methods: Typically developing children aged 12-18 years were randomised to right M1 anodal tDCS, HD-tDCS, or Sham during training of their left-hand on the Purdue Pegboard Task (PPT) over 5 days. Bilateral motor mapping was performed at baseline (pre), day 5 (post), and 6-weeks retention time (RT). Primary muscle was the first dorsal interosseous (FDI) with secondary muscles of abductor pollicis brevis (APB) and adductor digiti minimi (ADM). Primary mapping outcomes were volume (mm²/mV) and area (mm²). Secondary outcomes were centre of gravity (COG, mm) and hotspot magnitude (mV). Linear mixed-effects modelling was employed to investigate effects of time and stimulation type (tDCS, HD-tDCS, Sham) on motor map characteristics. Results: Twenty-four right-handed participants (median age 15.5 years, 52% female) completed the study with no serious adverse events or dropouts. Quality maps could not be obtained in two participants. No effect of time or group were observed on map area or volume. LFDI COG (mm) differed in the medial-lateral plane (x-axis) between tDCS and Sham (p = 0.038) from pre-to-post mapping sessions. Shifts in map COG were also observed for secondary left-hand muscles. Map metrics did not correlate with behavioural changes. Conclusion: Robotic TMS mapping can safely assess motor cortex neurophysiology in children undergoing motor learning and neuromodulation interventions. Large effects on map area and volume were not observed while changes in COG may occur. Larger controlled studies are required to understand the role of motor maps in interventional neuroplasticity in children.

The effects of physical training versus combined action observation and motor imagery in conjunction with physical training on upper-extremity performance

INTRODUCTION

Combined action observation and motor imagery training (AO+MI training), which involves motor imagery during action observation and physical training, has been attracting attention as an effective strategy for learning motor skills. However, little has been reported on the effects of AO+MI training. In the present study, we compared the effects of AO+MI training to the effects of physical training on upper-extremity performance.

MATERIALS AND METHODS

Ninety-six healthy participants were randomly assigned to either the control group or the experimental group. Sport stacking, which is often used to evaluate upper-extremity performance, was adopted for the task. The experiment was scheduled for three days. The training was 20 min per day. The control group performed only physical training, while the experimental group performed four 5-min AO+MI training sessions. Time taken to complete a sport stacking try (task completion time) was defined as the index of speed of upper-extremity performance and number of fallen cups as the index of its accuracy. The outcomes within each group and between the two groups were compared.

RESULTS

Both AO+MI training and physical training showed reduced task completion time and increased number of fallen cups. There were no significant differences in the degree of changes between the groups.

CONCLUSION

Results from the present study showed that AO+MI training and physical training had almost the same influence on upper-extremity performance in the early stages of learning sport stacking. This result suggests that AO+MI training may be an effective and low-burden training method for participants.

Prefrontal high definition cathodal tDCS modulates executive functions only when coupled with moderate aerobic exercise in healthy persons

Transcranial direct current stimulation (tDCS) is a promising tool to enhance cognitive performance. However, its effectiveness has not yet been unequivocally shown. Thus, here we tested whether coupling tDCS with a bout of aerobic exercise (AE) is more effective in modulating cognitive functions than tDCS or AE alone. One hundred twenty-two healthy participants were assigned to five randomized controlled crossover experiments. Two multimodal target experiments (EXP-4: anodal vs. sham tDCS during AE; EXP-5: cathodal vs. sham tDCS during AE) investigated whether anodal (a-tDCS) or cathodal tDCS (c-tDCS) applied during AE over the left dorsolateral prefrontal cortex (left DLPFC) affects executive functioning (inhibition ability). In three unimodal control experiments, the participants were either stimulated (EXP-1: anodal vs. sham tDCS, EXP-2: cathodal vs. sham tDCS) or did AE (EXP-3: AE vs. active control). Participants performed an Eriksen flanker task during ergometer cycling at moderate intensity (in EXP. 3-5). Only c-tDCS during AE had a significant adverse effect on the inhibition task, with decreased accuracy. This outcome provides preliminary evidence that c-tDCS during AE over the left DLPFC might effectively modulate inhibition performance compared to c-tDCS alone. However, more systematic research is needed in the future.

The Effect of Parietal and Cerebellar Transcranial Direct Current Stimulation on Bimanual Coordinated Adaptive Motor Learning

Abstract. Many daily activities, such as typing, eating, playing the piano, and passing the ball in volleyball, require the proficient coordination of both hands. In this study, the effects of anodal transcranial direct current stimulation (atDCS) on the acquisition, retention, and transfer of bimanual adaptive motor tasks were investigated. To this end, 64 volunteers ( Mage = 24.36 years; SD = 2.51; 16 females) participated in this double-blind study and were categorized randomly into 4 groups. During the pretest, posttest, 24-h and 48-h retention, and transfer tests, two forms of bimanual coordination (BC) of the Vienna test system were performed. Between the pretest and posttest, all participants were trained in a bimanual coordination adaptive task with concurrent brain stimulation (1.5 mA for 15 min) for two consecutive days. The first experimental group (parietal-stim) received atDCS over the right parietal cortex (P4), while the second experimental group (cerebellar-stim) received atDCS over the bilateral cerebellum (2.5 cm bilateral to the inion). The third group (sham) received a sham stimulation. Finally, the control group did not receive any stimulation at all (control). Repeated-measure analysis of variance (ANOVARM) results indicated that parietal tDCS affected motor performance in the posttest, while overall mean duration and overall error mean duration of movement decreased. The results also revealed a significant impact of cerebellar tDCS on the posttest, 24-h and 48-h retention, and transfer tests. The overall mean duration and overall error mean durations of movement in this group were significantly lower than those in the other groups. Accordingly, we found evidence that atDCS over the cerebellum leads to more improvement in motor performance and transfer in a bimanual coordination task than atDCS over the right parietal. Finally, these results point to the possibly beneficial application of atDCS for learning and recovery of bimanual motor skills, especially when subjects are faced with a new challenging situation.

Beyond the target area: an integrative view of tDCS-induced motor cortex modulation in patients and athletes

Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique used to modulate neural tissue. Neuromodulation apparently improves cognitive functions in several neurologic diseases treatment and sports performance. In this study, we present a comprehensive, integrative review of tDCS for motor rehabilitation and motor learning in healthy individuals, athletes and multiple neurologic and neuropsychiatric conditions. We also report on neuromodulation mechanisms, main applications, current knowledge including areas such as language, embodied cognition, functional and social aspects, and future directions. We present the use and perspectives of new developments in tDCS technology, namely high-definition tDCS (HD-tDCS) which promises to overcome one of the main tDCS limitation (i.e., low focality) and its application for neurological disease, pain relief, and motor learning/rehabilitation. Finally, we provided information regarding the Transcutaneous Spinal Direct Current Stimulation (tsDCS) in clinical applications, Cerebellar tDCS (ctDCS) and its influence on motor learning, and TMS combined with electroencephalography (EEG) as a tool to evaluate tDCS effects on brain function.

The Impact of Transcranial Direct Current Stimulation on Upper-Limb Motor Performance in Healthy Adults: A Systematic Review and Meta-Analysis

Background: Transcranial direct current stimulation (tDCS) has previously been reported to improve facets of upper limb motor performance such as accuracy and strength. However, the magnitude of motor performance improvement has not been reviewed by contemporaneous systematic review or meta-analysis of sham vs. active tDCS.

Objective: To systematically review and meta-analyse the existing evidence regarding the benefits of tDCS on upper limb motor performance in healthy adults.

Methods: A systematic search was conducted to obtain relevant articles from three databases (MEDLINE, EMBASE, and PsycINFO) yielding 3,200 abstracts. Following independent assessment by two reviewers, a total of 86 articles were included for review, of which 37 were deemed suitable for meta-analysis.

Results: Meta-analyses were performed for four outcome measures, namely: reaction time (RT), execution time (ET), time to task failure (TTF), and force. Further qualitative review was performed for accuracy and error. Statistically significant improvements in RT (effect size −0.01; 95% CI −0.02 to 0.001, p = 0.03) and ET (effect size −0.03; 95% CI −0.05 to −0.01, p = 0.017) were demonstrated compared to sham. In exercise tasks, increased force (effect size 0.10; 95% CI 0.08 to 0.13, p < 0.001) and a trend towards improved TTF was also observed.

Conclusions: This meta-analysis provides evidence attesting to the impact of tDCS on upper limb motor performance in healthy adults. Improved performance is demonstrable in reaction time, task completion time, elbow flexion tasks and accuracy. Considerable heterogeneity exists amongst the literature, further confirming the need for a standardised approach to reporting tDCS studies.

A Review of Acute Aerobic Exercise and Transcranial Direct Current Stimulation Effects on Cognitive Functions and Their Potential Synergies

Today, several pharmaceutic and non-pharmaceutic approaches exist to treat psychiatric and neurological diseases. Because of the lack of treatment procedures that are medication free and without severe side effects, transcranial direct current stimulation (tDCS) and aerobic exercise (AE) have been tested to explore the potential for initiating and modulating neuroplasticity in the human brain. Both tDCS and AE could support cognition and behavior in the clinical and non-clinical context to improve the recovery process within neurological or psychiatric conditions or to increase performance. As these techniques still lack meaningful effects, although they provide multiple beneficial opportunities within disease and health applications, there is emerging interest to find improved tDCS and AE protocols. Since multimodal approaches could provoke synergetic effects, a few recent studies have begun to combine tDCS and AE within different settings such as in cognitive training in health or for treatment purposes within clinical settings, all of which show superior effects compared to single technique applications. The beneficial outcomes of both techniques depend on several parameters and the understanding of neural mechanisms that are not yet fully understood. Recent studies have begun to directly combine tDCS and AE within one session, although their interactions on the behavioral, neurophysiological and neurochemical levels are entirely unclear. Therefore, this review: (a) provides an overview of acute behavioral, neurophysiological, and neurochemical effects that both techniques provoke within only one single application in isolation; (b) gives an overview regarding the mechanistic pathways; and (c) discusses potential interactions and synergies between tDCS and AE that might be provoked when directly combining both techniques. From this literature review focusing primarily on the cognitive domain in term of specific executive functions (EFs; inhibition, updating, and switching), it is concluded that a direct combination of tDCS and AE provides multiple beneficial opportunities for synergistic effects. A combination could be useful within non-clinical settings in health and for treating several psychiatric and neurologic conditions. However, there is a lack of research and there are several possibly interacting moderating parameters that must be considered and more importantly must be systematically investigated in the future.

Physics of Transcranial Direct Current Stimulation Devices and Their History

Transcranial direct current stimulation (tDCS) devices apply direct current through electrodes on the scalp with the intention to modulate brain function for experimental or clinical purposes. All tDCS devices include a current controlled stimulator, electrodes that include a disposable electrolyte, and headgear to position the electrodes on the scalp. Transcranial direct current stimulation dose can be defined by the size and position of electrodes and the duration and intensity of current applied across electrodes. Electrode design and preparation are important for reproducibility and tolerability. High-definition tDCS uses smaller electrodes that can be arranged in arrays to optimize brain current flow. When intended to be used at home, tDCS devices require specific device design considerations. Computational models of current flow have been validated and support optimization and hypothesis testing. Consensus on the safety and tolerability of tDCS is protocol specific, but medical-grade tDCS devices minimize risk.

Effects of tDCS on Bimanual Motor Skills: A Brief Review

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that allows the modulation of cortical excitability as well as neuroplastic reorganization using a weak constant current applied through the skull on the cerebral cortex. TDCS has been found to improve motor performance in general and motor learning in particular. However, these effects have been reported almost exclusively for unimanual motor tasks such as serial reaction time tasks, adaptation tasks, or visuo-motor tracking. Despite the importance of bimanual actions in most activities of daily living, only few studies have investigated the effects of tDCS on bimanual motor skills. The objectives of this review article are: (i) to provide a concise overview of the few existing studies in this area; and (ii) to discuss the effects of tDCS on bimanual motor skills in healthy volunteers and patients suffering from neurological diseases. Despite considerable variations in stimulation protocols, the bimanual tasks employed, and study designs, the data suggest that tDCS has the potential to enhance bimanual motor skills. The findings imply that the effects of tDCS vary with task demands, such as complexity and the level of expertise of the participating volunteers. Nevertheless, optimized stimulation protocols tailored to bimanual tasks and individual performance considering the underlying neural substrates of task execution are required in order to probe the effectiveness of tDCS in greater detail, thus creating an opportunity to support motor recovery in neuro-rehabilitation.

Cathodal Transcranial Direct Current Stimulation Improves Focal Hand Dystonia in Musicians: A Two-Case Study

Focal hand dystonia (FHD) in musicians is a movement disorder causing abnormal movements and irregularities in playing. Since weak electrical currents applied to the brain induce persistent excitability changes in humans, cathodal tDCS was proposed as a possible non-invasive approach for modulating cortical excitability in patients with FHD. However, the optimal targets and modalities have still to be determined. In this pilot study, we delivered cathodal (2 mA), anodal (2 mA) and sham tDCS over the motor areas bilaterally for 20 min daily for five consecutive days in two musicians with FHD. After cathodal tDCS, both patients reported a sensation of general wellness and improved symptoms of FHD. In conclusion, our pilot results suggest that cathodal tDCS delivered bilaterally over motor-premotor (M-PM) cortex for 5 consecutive days may be effective in improving symptoms in FHD.