Raised corticomotor excitability of M1 forearm area following anodal tDCS is sustained during robotic wrist therapy in chronic stroke

Abstract

Purpose: Anodal transcranial direct current stimulation (tDCS) can transiently increase corticomotor excitability of intrinsic hand muscles and improve upper limb function in patients with chronic stroke. As a preliminary study, we tested whether increased corticomotor excitability would be similarly observed in muscles acting about the wrist, and remain present during robotic training involving active wrist movements, in six chronic stroke patients with residual motor deficit.

Methods: Transcranial magnetic stimulation (TMS) generated motor evoked potentials (MEP) in the flexor carpi radialis (FCR) and provided a measure of corticomotor excitability and short-interval cortical inhibition (SICI) before and immediately after a period of tDCS (1 mA, 20 min, anode and TMS applied to the lesioned hemisphere), and robotic wrist training (1hr).

Results: Following tDCS, the same TMS current strength evoked an increased MEP amplitude (mean 168 +/- 22%SEM; p < 0.05), that remained increased after robot training (166 +/- 23%; p < 0.05). Conditioned MEPs were of significantly lower amplitude relative to unconditioned MEPs prior to tDCS (62 +/- 6%, p < 0.05), but not after tDCS (89 +/- 14%, p = 0.40), or robot training (91 +/- 8%, p = 0.28), suggesting that the increased corticomotor excitability is associated with reduced intracortical inhibition.

Conclusion: The persistence of these effects after robotic motor training, indicates that a motor learning and retraining program can co-exist with tDCS-induced changes in cortical motor excitability, and supports the concept of combining brain stimulation with physical therapy to promote recovery after brain injury.

Figures

Fig. 1

Supplementary clinical information for the study participants.

Fig. 2

Wrist Robot. The top row shows the device during therapy at Burke Rehabilitation Hospital. The bottom row shows a solid view of the design. (Colours are visible in the online version of the article www.iospress.nl.)

Fig. 3

Mean (± SEM) MEP amplitude from across subjects. MEPs were recorded from the FCR muscle during a low-level isometric wrist flexion, before and immediately following 20min anodal brain stimulation (tDCS), then again after 1hr of robotic wrist therapy. Following tDCS, MEP amplitude was significantly elevated, and remained significantly elevated after robotic therapy.

Fig. 4

Sample overlaid MEPs from one subject, showing the marked increase in MEP amplitude following 20min anodal brain stimulation, which remains present following the 1hr robotic therapy.

Fig. 5

Percentage reduction in the conditioned compared to the unconditioned MEP amplitude before and after tDCS, then again after robot therapy, showing the significant reduction in conditioned MEP amplitude before intervention, is not observed after tDCS or robot therapy. This demonstrates reduced short-interval cortical inhibition resulting from tDCS, that is sustained during robotic therapy and may be implicated in the corresponding increase in corticomotor excitability.