Predicting behavioural response to TDCS in chronic motor stroke

Jacinta O'Shea,Marie-Hélène Boudrias,Charlotte Jane Stagg,Velicia Bachtiar,Udo Kischka,Jakob Udby Blicher,Heidi Johansen-Berg

doi:10.1016/j.neuroimage.2013.05.096

Abstract

Transcranial direct current stimulation (TDCS) of primary motor cortex (M1) can transiently improve paretic hand function in chronic stroke. However, responses are variable so there is incentive to try to improve efficacy and or to predict response in individual patients. Both excitatory (Anodal) stimulation of ipsilesional M1 and inhibitory (Cathodal) stimulation of contralesional M1 can speed simple reaction time. Here we tested whether combining these two effects simultaneously, by using a bilateral M1–M1 electrode montage, would improve efficacy. We tested the physiological efficacy of Bilateral, Anodal or Cathodal TDCS in changing motor evoked potentials (MEPs) in the healthy brain and their behavioural efficacy in changing reaction times with the paretic hand in chronic stroke. In addition, we aimed to identify clinical or neurochemical predictors of patients' behavioural response to TDCS. There were three main findings: 1) unlike Anodal and Cathodal TDCS, Bilateral M1–M1 TDCS (1mA, 20min) had no significant effect on MEPs in the healthy brain or on reaction time with the paretic hand in chronic stroke patients; 2) GABA levels in ipsilesional M1 predicted patients' behavioural gains from Anodal TDCS; and 3) although patients were in the chronic phase, time since stroke (and its combination with Fugl–Meyer score) was a positive predictor of behavioural gain from Cathodal TDCS. These findings indicate the superiority of Anodal or Cathodal over Bilateral TDCS in changing motor cortico-spinal excitability in the healthy brain and in speeding reaction time in chronic stroke. The identified clinical and neurochemical markers of behavioural response should help to inform the optimization of TDCS delivery and to predict patient outcome variability in future TDCS intervention studies in chronic motor stroke.

Highlights

Stroke is a leading cause of life-long disability (Adamson et al, 2004)
To test the hypothesis that Transcranial direct current stimulation (TDCS) would change Motor-evoked potentials (MEPs) amplitude in a manner that varied by both stimulation polarity and hand, RM ANOVA was conducted on %ΔMEP data with factors of TDCS (Anodal, Cathodal, Bilateral), Hand (Right, Left) and Time (Post 1, 2, 3, 4)
Since we had no hypothesis about Time, the data were pooled over Time and a follow-up RM ANOVA re-confirmed the main effects of both TDCS (p b .001) and Hand (p b .001)

Summary

Introduction

Stroke is a leading cause of life-long disability (Adamson et al, 2004). Treatments that can improve function and reduce disability once patients have reached the chronic phase are limited. Anodal stimulation increases while Cathodal stimulation decreases the excitability of primary motor cortex (M1) (Nitsche and Paulus, 2000). Both Anodal stimulation of ipsilesional M1 and Cathodal stimulation of contralesional M1 have been shown to induce. Short-lived improvements in paretic hand function after stroke (Fregni et al, 2005; Hummel et al, 2006). Both interventions increase task-related functional motor activity in ipsilesional M1 and in a number of inter-connected secondary motor areas (Stagg et al, 2012). On the question of which of these two stimulation strategies should have greater therapeutic efficacy for a given individual, the answer is unclear, partly because Anodal and Cathodal TDCS are rarely compared directly in the same patients ( see Fregni et al, 2005; Stagg et al, 2012)

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Conclusion