Neurophysiological and behavioural effects of dual-hemisphere transcranial direct current stimulation on the proximal upper limb

Effects of repeated unihemispheric concurrent dual-site tDCS and virtual reality games on motor coordination of sedentary adolescent girls

BACKGROUND

This study investigated the effects of repetitive unihemispheric concurrent dual-site anodal transcranial direct current stimulation (a-tDCSUHCDS) associated with the use of virtual reality games (VR) on the motor coordination of sedentary adolescent girls.

METHODS

Thirty-six inactive adolescent girls were randomly assigned into 3 groups (n = 12 per group): (1) VR + a-tDCSUHCDS, (2) VR + sham-tDCSUHCDS, and (3) Control. The VR + a-tDCSUHCDS and VR + s-tDCSUHCDS groups received the intervention three times a week for four weeks. In each experimental session, participants first received either 20 min of a-tDCSUHCDS (2 mA at each anodal electrode) targeting the primary motor cortex (M1) and the left dorsolateral prefrontal cortex (DLPFC) or sham and then performed VR for 1 h. The control group received no intervention. Eye-hand coordination (EHC) and bimanual coordination (BC) were measured at baseline, post-intervention, and two weeks later (retention test) using the automatic scoring mirror tracer and continuous two-arm coordination test, respectively.

RESULTS

Results showed that the EHC was significantly higher in the VR + a-tDCS and VR + s-tDCS groups at post-intervention (all ps< 0.001) and the retention test (all ps< 0.001) compared to the control group. Moreover, the EHC was significantly higher in the VR + a-tDCS group compared to the VR + s-tDCS group (p = 0.024) at the retention. Similarly, VR + a-tDCS and VR + s-tDCS improved BC compared to the control group at post-intervention (all ps< 0.001) and retention test (all ps< 0.001). In addition, higher BC was observed in the VR + a-tDCS group compared to the VR + s-tDCS group (p< 0.001) at the retention test.

CONCLUSIONS

Our results suggest that adding a-tDCSUHCDS to VR over 12 sessions may have an additional effect on VR training for improving and retaining motor coordination in sedentary adolescent girls.

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.

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.

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.

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.