Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation used for improving cognitive functions via delivering weak electrical stimulation with a certain frequency. This systematic review and meta-analysis investigated the effects of tACS protocols on cognitive functions in healthy young adults. We identified 56 qualified studies that compared cognitive functions between tACS and sham control groups, as indicated by cognitive performances and cognition-related reaction time. Moderator variable analyses specified effect size according to (a) timing of tACS, (b) frequency band of simulation, (c) targeted brain region, and (b) cognitive domain, respectively. Random-effects model meta-analysis revealed small positive effects of tACS protocols on cognitive performances. The moderator variable analyses found significant effects for online-tACS with theta frequency band, online-tACS with gamma frequency band, and offline-tACS with theta frequency band. Moreover, cognitive performances were improved in online- and offline-tACS with theta frequency band on either prefrontal and posterior parietal cortical regions, and further both online- and offline-tACS with theta frequency band enhanced executive function. Online-tACS with gamma frequency band on posterior parietal cortex was effective for improving cognitive performances, and the cognitive improvements appeared in executive function and perceptual-motor function. These findings suggested that tACS protocols with specific timing and frequency band may effectively improve cognitive performances.

Objective:To provide clear evidence in support of the use of exercise to improve depressive symptoms in patients with Parkinson’s disease (PD), and to investigate whether this effect differs by exercise type and intensity.Methods:Three independent reviewers searched for randomized controlled trials that applied exercise interventions with depressive symptoms as an outcome measure for patients with PD on PubMed and Web of Science up to February 28, 2022. Random effects meta-analyses were performed, in which standardized mean differences (SMDs) between the effects of exercise and control interventions on depressive symptoms with 95% confidence intervals (CIs) were calculated.Results:A total of 19 randomized controlled trials including 1,302 PD patients were eligible for meta-analysis, and we obtained 23 comparisons from the included studies for data synthesis. Physical exercise interventions showed significant effects on the reduction in depressive symptoms in PD patients (SMD=0.829; 95% CI=0.516 to 1.142; P<0.001). Moderator analyses on exercise type revealed significant positive effects for combined exercise interventions (SMD=1.111; 95% CI=0.635 to 1.587; P<0.001), whereas aerobic training alone failed to show significant effects (SMD=0.202; 95% CI =-0.045 to 0.449; P=0.108). With respect to exercise intensity, both light-to-moderate intensity exercises (SMD=0.971; 95% CI=0.521 to 1.421; P<0.001) and moderate-to-vigorous intensity exercises (SMD=0.779; 95% CI=0.407 to 1.152; P<0.001) significantly improved depressive symptoms with a small difference between the exercise intensities.Conclusion:Our results suggest that physical exercise has significant antidepressant effects in PD patients. These effects appeared to be more closely associated with exercise type than intensity. Different types of exercise interventions may result in greater benefit and require further investigation.

Transcranial direct current stimulation (tDCS) is one of the non-invasive brain stimulation techniques that can improve motor functions. As bimanual motor actions require high motor cortical activations between hemispheres, applying bilateral anodal stimulation on left and right sides of primary motor cortex (M1) can improve for improvements in bimanual motor tasks. This study investigated which bilateral tDCS protocol effectively improves bimanual hand-grip force control capabilities in healthy young adults. We used three different bilateral tDCS protocols: (a) dual-anodal stimulation on the M1 of bilateral hemispheres (Bi-AA), (b) anodal–cathodal stimulation on the M1 of dominant and nondominant hemispheres (Bi-AC), and (c) sham stimulation (Sham). The results indicated that applying the Bi-AA significantly improved bilateral motor synergies estimated by uncontrolled manifold analysis relative to Sham. However, these differences were not observed in the comparison between Bi-AA and Bi-AC as well as between Bi-AC and Sham. These findings suggest that facilitating motor cortical activations between both hemispheres may be an additional option for advancing interlimb motor coordination patterns.