Nyeonju Kang

Transcranial direct current stimulation facilitates motor learning post-stroke: a systematic review and meta-analysis

Transcranial direct current stimulation (tDCS) is an attractive protocol for stroke motor recovery. The current systematic review and meta-analysis investigated the effects of tDCS on motor learning post-stroke. Specifically, we determined long-term learning effects by examining motor improvements from baseline to at least 5 days after tDCS intervention and motor practise. 17 studies reported long-term retention testing (mean retention interval=43.8 days; SD=56.6 days) and qualified for inclusion in our meta-analysis. Assessing primary outcome measures for groups that received tDCS and motor practise versus sham control groups created 21 valid comparisons: (1) 16 clinical assessments and (2) 5 motor skill acquisition tests. A random effects model meta-analysis showed a significant overall effect size=0.59 (p<0.0001; low heterogeneity, T2=0.04; I2=22.75%; and high classic fail-safe N=240). 4 moderator variable analyses revealed beneficial effects of tDCS on long-term motor learning: (1) stimulation protocols: anodal on the ipsilesional hemisphere, cathodal on the contralesional hemisphere, or bilateral; (2) recovery stage: subacute or chronic stroke; (3) stimulation timing: tDCS before or during motor practise; and (4) task-specific training or conventional rehabilitation protocols. This robust meta-analysis identified novel long-term motor learning effects with tDCS and motor practise post-stroke.

Does transcranial direct current stimulation enhance cognitive and motor functions in the ageing brain? A systematic review and meta- analysis.

The use of transcranial direct current stimulation (tDCS) to enhance cognitive and motor functions has enjoyed a massive increase in popularity. Modifying neuroplasticity via non-invasive cortical stimulation has enormous potential to slow or even reverse declines in functions associated with ageing. The current meta-analysis evaluated the effects of tDCS on cognitive and motor performance in healthy older adults. Of the 81 studies identified, 25 qualified for inclusion. A random effects model meta-analysis revealed a significant overall standardized mean difference equal to 0.53 (SE=0.09; medium heterogeneity: I(2)=57.08%; and high fail-safe: N=448). Five analyses on moderator variables indicated significant tDCS beneficial effects: (a) on both cognitive and motor task performances, (b) across a wide-range of cognitive tasks, (c) on specific brain areas, (d) stimulation offline (before) or online (during) the cognitive and motor tasks. Although the meta-analysis revealed robust support for enhancing both cognitive and motor performance, we outline a number of caveats on the use of tDCS.

Force control in chronic stroke.

Force control deficits are common dysfunctions after a stroke. This review concentrates on various force control variables associated with motor impairments and suggests new approaches to quantifying force control production and modulation. Moreover, related neurophysiological mechanisms were addressed to determine variables that affect force control capabilities. Typically, post stroke force control impairments include: (a) decreased force magnitude and asymmetrical forces between hands, (b) higher task error, (c) greater force variability, (d) increased force regularity, and (e) greater time-lag between muscular forces. Recent advances in force control analyses post stroke indicated less bimanual motor synergies and impaired low-force frequency structure. Brain imaging studies demonstrate possible neurophysiological mechanisms underlying force control impairments: (a) decreased activation in motor areas of the ipsilesional hemisphere, (b) increased activation in secondary motor areas between hemispheres, (c) cerebellum involvement, and (d) relatively greater interhemispheric inhibition from the contralesional hemisphere. Consistent with identifying neurophysiological mechanisms, analyzing bimanual motor synergies as well as low-force frequency structure will advance our understanding of post stroke force control.

Non-Invasive Brain Stimulation Improves Paretic Limb Force Production: A Systematic Review and Meta-Analysis

BACKGROUND Non-invasive brain stimulation (NIBS) facilitates motor improvements post stroke. Transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) are representative NIBS techniques frequently used in stroke motor rehabilitation. Our primary question is: Do these two techniques improve force production capability in paretic limbs? OBJECTIVE The current systematic review and meta-analysis investigated the effects of tDCS and rTMS on paretic limb force production in stroke survivors. METHODS Our comprehensive search identified 23 studies that reported changes in force production following tDCS or rTMS interventions. Each used random assignment and a sham control group. The 23 qualified studies in our meta-analysis generated 29 comparisons: 14 tDCS and 15 rTMS comparisons. RESULTS Random effects models indicated improvements in paretic limb force after tDCS and rTMS rehabilitation. We found positive effects on force production in the two sets of stimulation protocols: (a) increasing cortical activity in the ipsilesional hemisphere and (b) decreasing cortical activity in the contralesional hemisphere. Moreover, across acute, subacute, and chronic phases, tDCS and rTMS improved force production. CONCLUSION Cumulative meta-analytic results revealed that tDCS and rTMS rehabilitation protocols successfully improved paretic limb force production capabilities.

Bimanual force variability in chronic stroke: With and without visual information

Visual information is critical to producing and controlling force output to achieve targeted levels. This study investigated bimanual force control in chronic stroke individuals while manipulating visual information. Nine chronic stroke individuals and nine age-matched controls executed bimanual wrist and finger extension at 5% of maximum voluntary contraction. Bimanual force control outcome measures included: (a) coefficient of variation, (b) approximate entropy, and (c) bimanual coordination. Without visual information, chronic stroke individuals displayed less force variability and more regular force production in comparison to age-matched controls. These findings suggest that chronic stroke individuals depended on visual information during bimanual force execution.

Bimanual force variability and chronic stroke: asymmetrical hand control.

The purpose of this study was to investigate force variability generated by both the paretic and non-paretic hands during bimanual force control. Nine chronic stroke individuals and nine age-matched individuals with no stroke history performed a force control task with both hands simultaneously. The task involved extending the wrist and fingers at 5%, 25%, and 50% of maximum voluntary contraction. Bimanual and unimanual force variability during bimanual force control was determined by calculating the coefficient of variation. Analyses revealed two main findings: (a) greater bimanual force variability in the stroke group than the control group and (b) increased force variability by the paretic hands during bimanual force control in comparison to the non-paretic hands at the 5% and 25% force production conditions. A primary conclusion is that post stroke bimanual force variability is asymmetrical between hands.

Paretic hand unimanual force control: Improved submaximal force production and regularity.

The purpose was to investigate force control capabilities in paretic hands during unimanual movements after coupled bimanual movement training and neuromuscular stimulation on impaired muscles. Nineteen chronic stroke participants completed 90 min of rehabilitation per week for six consecutive weeks. Before and after training, volunteers performed unimanual submaximal force control tasks at 5% and 50% of maximum voluntary contraction with their paretic and non-paretic hands. Force control measures included submaximal force production, force variability, accuracy, and regularity. Two major findings on paretic hands after training revealed: (a) greater submaximal force production across force levels and (b) less regular force outputs. Paretic hand control improved after coupled bimanual movement training as evidenced by submaximal force production and force regularity.

Age-related differences in bimanual movements: A systematic review and meta-analysis

Background: With increasing age motor functions decline. The additional challenges of executing bimanual movements further hinder motor functions in older adults. The current systematic review and meta‐analysis determined the effects of healthy aging on performance in bimanual movements as compared to younger adults. Methods: Our comprehensive search identified 27 studies that reported bimanual movement performance measures. Each study included a between groups comparison of older (mean age = 68.79 years) and younger adults (mean age = 23.14 years). The 27 qualified studies generated 40 total outcome measure comparisons: (a) accuracy: 18, (b) variability: 14, and (c) movement time: eight. Results: Our meta‐analysis conducted on a random effects model identified a relatively large negative standardized mean difference effect (ES = −0.93). This indicates that older adults exhibited more impaired bimanual movement performance in comparison to younger adults in our group of studies. Specifically, a moderator variable analysis revealed large negative effects in both accuracy (ES = −0.94) and variability (ES = −1.00), as well as a moderate negative effect (ES = −0.71) for movement time. These findings indicate that older adults displayed reduced accuracy, greater variability, and longer execution time when executing bimanual movements. Conclusion: These meta‐analytic findings revealed that aging impairs bimanual movement performance. HighlightsPrevious bimanual movements and aging studies report conflicting results.Current meta‐analysis revealed impaired bimanual movements in older adults.Older adults showed less accuracy, more variability, and longer movement time.

Bilateral synergy as an index of force coordination in chronic stroke

Dysfunction in bilateral coordination post-stroke is responsible for impaired bilateral movements. This study examined bilateral synergies using the uncontrolled manifold (UCM) approach while individuals in a chronic stage after stroke executed bilateral isometric force control at three submaximal force levels. Nine patients with stroke and nine age-matched healthy controls performed 24 trials of wrist and fingers extension at 5, 25, and 50% of MVC. The UCM findings revealed: (a) decreased bilateral synergies in patients with stroke as compared to controls at 50% of MVC and (b) reduced good variability and increased bad variability components in patients with stroke at 50% of MVC. Moreover, correlation analyses across both groups showed that a reduction of bilateral synergies was related to increased force error at 50% of MVC and an inconsistent force ratio between the two hands across multiple trials correlated with increased good and bad variability at 5% of MVC. Current findings indicate that quantifying bilateral synergies may provide meaningful profiles for estimating impairments as well as improvements of cooperative behaviors between two hands post-stroke.

Increased visual information gain improves bimanual force coordination.

Bimanual force control requiring asymmetrical forces between limbs is more challenging than bimanual force control when the limbs produce symmetrical forces. Previous studies investigated visual information gains between 8 and 80 pixels/N to facilitate asymmetrical force control. Given that previous studies limited visual information gain to 80 pixels/N, the current experiment expanded the range by increasing visual information gains (8, 80, 256, and 512 pixels/N). A second manipulation involved three task constraint coefficients imposed on bimanual force control: (a) left-biased, (b) right-biased, and (c) equal-biased. Analyses of 15 right-handed adult volunteers revealed a decrease in bimanual force variability and more negative correlation coefficient with increased visual information gain in the equal biased condition. Significant reductions in bimanual force variability were found between 8 and 80 pixels/N. In contrast, significant improvements in coordination patterns between hands continued up to 256 pixels/N. These novel findings demonstrate that bimanual force coordination was more sensitive to an increase in visual information gains (>80 pixels/N) than bimanual force variability.