The comparative effects of anodal and cathodal trans-cranial direct current stimulation on balance and posture: A systematic review of literature and meta-analysis.

Application of anodal trans-cranial direct current stimulation (a-tDCS) versus cathodal tDCS (c-tDCS) can influence the physiological results of tDCS intervention on postural control and balance in patients or healthy adults. According to the evidence, some studies demonstrated that postural control or balance is facilitated by the application of the a-tDCS more than the c-tDCS. On the other hand, some studies indicated that there were no significant differences between a-tDCS and c-tDCS. In contrast, other studies have shown a more significant effect of c-tDCS than a-tDCS on postural control and balance. This study aimed to systematically review the studies which investigated the effectiveness of a-tDCS and c-tDCS intervention on postural control and balance. The search was performed from databases in Google Scholar, PubMed, Elsevier, Medline, Ovid, and Science Direct with the keywords of balance, balance test, postural control, postural stability, postural sway, posture, postural balance, trans-cranial direct current stimulation, tDCS, neuromodulator, neurostimulation, tDCS, a-tDCS or anodal tDCS, c-tDCS or cathodal tDCS from 2000 to 2022. The results confirmed that the study population was a key factor in determining the study's findings. Data meta-analysis showed no significant differences between active tDCS and sham tDCS on postural control in healthy individuals (P > 0.05). In addition, the results indicated the efficacy of both a-tDCS over the affected motor cortex (M1) and c-tDCS over unaffected M1 as compared to sham tDCS on postural improvement in patients with stroke (P < 0.05), however, there were no differences between the two techniques on posture and balance in these patients.

Does anodal trans-cranial direct current stimulation of the damaged primary motor cortex affects wrist flexor muscle spasticity and also activity of the wrist flexor and extensor muscles in patients with stroke?: a Randomized Clinical Trial.

Spasticity is a common symptom in stroke survivors. This study is double-blinded, sham-controlled randomized, clinical trial with three parallel arms. The aim of the study was to investigate the effects of anodal trans-cranial direct current stimulation (a-tDCS) over the damaged primary motor cortex (M1) on spasticity of the wrist flexor and also the activity of wrist flexor and extensor muscles in sub-acute stroke patients. This study was performed on 32 stroke patients. The patients are assigned to three groups (intervention, sham, and control). All participants in the first two groups received 20-min concurrent M1 a-tDCS or sham tDCS and functional electrical stimulation (FES) for 10 sessions (5 sessions per week), while participants in control group were given only 20-min FES for 10 sessions. Modified Ashworth scale of wrist flexors and also electromyography (EMG) activity of flexor carpi radialis (FCR) and extensor carpi radialis (ECR) were recorded before, immediately, and 1 month after the interventions. A significant reduction was shown in the MAS and EMG activity of FCR muscle at passive rest position of the wrist, immediately and 1 month after the intervention in M1 a-tDCS compared to sham and control groups (p < 0.001). Also, the EMG activity of FCR and ECR muscles during active wrist flexion and extension increased immediately and 1 month after intervention in M1 a-tDCS compared to the other groups, respectively (p < 0.001). M1 a-tDCS can significantly decrease the spasticity of wrist flexor muscle and also increase the wrist flexor and extensor muscles activity in stroke patients during active flexion and extension.

The comparative effects of unilateral and bilateral transcranial direct current stimulation on motor learning and motor performance: A systematic review of literature and meta-analysis.

Application of unilateral tDCS (Uni-tDCS) vs. bilateral tDCS (Bi-tDCS) is another important factor that can affect the physiological results of tDCS intervention on motor learning and motor performance. According to the evidence, some studies indicated that motor performance or motor learning are facilitated in healthy individuals by application of the Bi-tDCS more than the Uni-tDCS. On the other hand, some studies showed that there was no significant differences between Uni-tDCS and Bi-tDCS; and both techniques were more effective than sham stimulation. In contrast, the other studies have shown more significant effectiveness of Uni-tDCS than Bi-tDCS on motor performance and motor learning. The aim of this study was to systematically review the studies which investigated the effectiveness of Uni-tDCS and Bi-tDCS intervention on the motor learning and motor performance. The search was performed from databases in the Google Scholar, PubMed, Elsevier, Medline, Ovid and Science Direct with the keywords of motor behavior, motor performance, motor learning, Bi-tDCS or bilateral tDCS, dual tDCS, Uni-tDCS or unilateral tDCS, anodal tDCS and cathodal tDCS from 2000 to 2019. The results indicated that the study population was a key factor in determining study's findings. Data meta-analysis showed that Uni-tDCS was more effective than Bi-tDCS in patients with stroke, while, Bi-tDCS was more effective than Uni-tDCS to improve motor learning and motor performance in healthy individuals.