Abstract
BackgroundDual transcranial direct current stimulation (tDCS) to the bilateral primary motor cortices (M1s) has potential benefits in chronic stroke, but its effects in subacute stroke, when behavioural effects might be expected to be greater, have been relatively unexplored. Here, we examined the neurophysiological effects and the factors influencing responsiveness of dual-tDCS in subacute stroke survivors.MethodsWe conducted a randomized sham-controlled crossover study in 18 survivors with first-ever, unilateral subcortical ischaemic stroke 2–4 weeks after stroke onset and 14 matched healthy controls. Participants had real dual-tDCS (with an ipsilesional [right for controls] M1 anode and a contralesional M1 [left for controls] cathode; 2 mA for 20mins) and sham dual-tDCS on separate days, with concurrent paretic [left for controls] hand exercise. Using transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG), we recorded motor evoked potentials (MEPs), the ipsilateral silent period (iSP), short-interval intracortical inhibition, and finger movement-related cortical oscillations before and immediately after tDCS.ResultsStroke survivors had decreased excitability in ipsilesional M1 with a relatively excessive transcallosal inhibition from the contralesional to ipsilesional hemisphere at baseline compared with controls, as quantified by decreased MEPs and increased iSP duration. Dual-tDCS led to increased MEPs and decreased iSP duration in ipsilesional M1. The magnitude of the tDCS-induced MEP increase in stroke survivors was predicted by baseline contralesional-to-ipsilesional transcallosal inhibition (iSP) ratio. Baseline post-movement synchronization in α-band activity in ipsilesional M1 was decreased after stroke compared with controls, and its tDCS-induced increase correlated with upper limb score in stroke survivors. No significant adverse effects were observed during or after dual-tDCS.ConclusionsTask-concurrent dual-tDCS in subacute stroke can safely and effectively modulate bilateral M1 excitability and inter-hemispheric imbalance and also movement-related α-activity.
Highlights
IntroductionDual transcranial direct current stimulation (tDCS) to the bilateral primary motor cortices (M1s) has potential benefits in chronic stroke, but its effects in subacute stroke, when behavioural effects might be expected to be greater, have been relatively unexplored
Dual transcranial direct current stimulation to the bilateral primary motor cortices (M1s) has potential benefits in chronic stroke, but its effects in subacute stroke, when behavioural effects might be expected to be greater, have been relatively unexplored
Stroke survivors had decreased baseline excitability in ipsilesional M1 compared with controls We first wanted to investigate whether there were any differences between stroke survivors and controls in baseline transcranial magnetic stimulation (TMS) measures, i.e. before transcranial direct current stimulation (tDCS) was applied
Summary
Dual transcranial direct current stimulation (tDCS) to the bilateral primary motor cortices (M1s) has potential benefits in chronic stroke, but its effects in subacute stroke, when behavioural effects might be expected to be greater, have been relatively unexplored. Motor evoked potentials (MEPs) typically increase following unilateral anodal tDCS and decrease following unilateral cathodal tDCS, with effects outlasting stimulation by minutes to hours [3]. This polarity-specific modulation has been suggested as a putative way to promote post-stroke motor recovery, either by enhancing ipsilesional M1 excitability with anodal tDCS or decreasing contralesional M1 excitability with cathodal tDCS [4]. Consistent with these behavioural findings, increased MEPs in the anodetargeted M1 and decreased MEPs in the cathodetargeted M1 after dual-tDCS have been demonstrated in most studies in healthy controls [10, 14,15,16,17], suggesting that dual-tDCS may result in additive effects of unilateral stimulation, these effects are not entirely consistent [18]
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