The effect of transcranial direct current stimulation (tDCS) on motor learning and corticospinal excitability in multiple sclerosis

Abstract

Introduction Recently, the transcranial application of weak direct currents (tDCS) has been promoted as a promising adjuvant therapy to modulate motor function in neural rehabilitation. Studies in stroke, Parkinson’s disease and healthy aging showed that a single session of anodal tDCS over the primary motor cortex (M1) was sufficient to significantly improve motor performance. Furthermore, tDCS induced improvements are often correlated with tDCS-induced enhancement in recruitment curves. Until now, there are no studies evaluating the effect of tDCS on cortical excitability in patients with MS. However, due to impairments in signal transfer between central and peripheral regions it’s not clear whether tDCS will modulate the targeted peripheral muscles. The present study aimed to answer the question whether a single session of anodal tDCS has the potential to modulate cortical excitability in the motor cortex of MS patients. Methods Twenty-seven patients with MS (8 men and 19 women) aged 27 to 65 years participated in this study (EDSS: 1.5 - 6.5). In two pseudo-randomized, counterbalanced sessions separated by at least a week, patients received either anodal tDCS (1mA, 20 min) or sham on the primary motor cortex (M1) contralateral to the most impaired hand. Recruitment curves measuring corticospinal excitability of the contralateral M1 were assessed with transcranial magnetic stimulation (TMS) before and after the intervention. Results A mixed model including fixed effects for CONDITION (tDCS and SHAM), TIME (PRE and POST), INTENSITY (70, 90, 110, 130, 150, 170 and 190% rMT) and their interactions only revealed a significant effect for INTENSITY (p < .0001). Post-hoc analysis only revealed a significant effect between PRE and POST in the tDCS group at 150% and 170% rMT (respectively, p = .037 and p = .009).

Conclusion tDCS is able to modulate cortical excitability in the motor cortex of mildly to more severe disabled MS-patients.