Abstract
Background: During recovery from stroke, the contralesional motor cortex (M1) may undergo maladaptive changes that contribute to impaired interhemispheric inhibition (IHI). Transcranial direct current stimulation (tDCS) with the cathode over contralesional M1 may inhibit this maladaptive plasticity, normalize IHI, and enhance motor recovery.Objective: The objective of this systematic review and meta-analysis was to evaluate available evidence to determine whether cathodal tDCS on contralesional M1 enhances motor re-learning or recovery post-stroke more than sham tDCS.Methods: We searched OVID Medline, Embase, and the Cochrane Central Register of Controlled Trials for participants with stroke (>1 week post-onset) with motor impairment and who received cathodal or sham tDCS to contralesional M1 for one or more sessions. The outcomes included a change in any clinically validated assessment of physical function, activity, or participation, or a change in a movement performance variable (e.g., time, accuracy). A meta-analysis was performed by pooling five randomized controlled trials (RCTs) and comparing the change in Fugl–Meyer upper extremity scores between cathodal and sham tDCS groups.Results: Eleven studies met the inclusion criteria. Qualitatively, four out of five cross-over design studies and three out of six RCTs reported a significant effect of cathodal vs. sham tDCS. In the quantitative synthesis, cathodal tDCS (n = 65) did not significantly reduce motor impairment compared to sham tDCS (n = 67; standardized mean difference = 0.33, z = 1.79, p = 0.07) with a little observed heterogeneity (I2 = 5%).Conclusions: The effects of cathodal tDCS to contralesional M1 on motor recovery are small and consistent. There may be sub-populations that may respond to this approach; however, further research with larger cohorts is required.
Highlights
More than 60% of stroke survivors have persistent motor deficits for months to years after stroke (1)
We performed a systematic review and meta-analysis to determine whether the existing evidence indicates that cathodal Transcranial direct current stimulation (tDCS) to contralesional M1 enhances motor performance and/or recovery after stroke
The pooled effect estimate favored cathodal tDCS in participants with chronic stroke: cathodal tDCS (n = 19) significantly reduced motor impairment compared to sham tDCS (n = 21) (SMD = 0.77, 95% CI = 0.11 to 1.44, p = 0.02, Figure 2)
Summary
More than 60% of stroke survivors have persistent motor deficits for months to years after stroke (1). Many tDCS applications in stroke are based on a model of interhemispheric inhibition (IHI) (4, 5) thought to regulate cortical excitability between left and right motor cortex via transcallosal fibers. The IHI model postulates that recovery is hindered because of reduced inhibition from ipsilesional motor cortex (M1) to contralesional M1. This leads to “over-active” contralesional networks that are thought to be less efficient or to even inhibit recruitment of damaged ipsilesional networks. During recovery from stroke, the contralesional motor cortex (M1) may undergo maladaptive changes that contribute to impaired interhemispheric inhibition (IHI). Transcranial direct current stimulation (tDCS) with the cathode over contralesional M1 may inhibit this maladaptive plasticity, normalize IHI, and enhance motor recovery
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