Bimanual motor skill learning after stroke: Combining robotics and anodal tDCS over the undamaged hemisphere: An exploratory study

Abstract

Background: Since a stroke can impair bimanual activities, enhancing bimanual cooperation through motor skill learning may improve neurorehabilitation. Therefore, robotics and neuromodulation with transcranial direct current stimulation (tDCS) are promising approaches. To date, tDCS has failed to enhance bimanual motor control after stroke possibly because it was not integrating the hypothesis that the undamaged hemisphere becomes the major poststroke hub for bimanual control.

Objective: We tested the following hypotheses: (I) In patients with chronic hemiparetic stroke training on a robotic device, anodal tDCS applied over the primary motor cortex of the undamaged hemisphere enhances bimanual motor skill learning compared to sham tDCS. (II) The severity of impairment correlates with the effect of tDCS on bimanual motor skill learning. (III) Bimanual motor skill learning is less efficient in patients than in healthy individuals (HI).

Methods: A total of 17 patients with chronic hemiparetic stroke and 7 healthy individuals learned a complex bimanual cooperation skill on the REAplan® neurorehabilitation robot. The bimanual speed/accuracy trade-off (biSAT), bimanual coordination (biCo), and bimanual force (biFOP) scores were computed for each performance. In patients, real/sham tDCS was applied in a crossover, randomized, double-blind approach.

Results: Compared to sham, real tDCS did not enhance bimanual motor skill learning, retention, or generalization in patients, and no correlation with impairment was noted. The healthy individuals performed better than patients on bimanual motor skill learning, but generalization was similar in both groups.

Conclusion: A short motor skill learning session with a robotic device resulted in the retention and generalization of a complex skill involving bimanual cooperation. The tDCS strategy that would best enhance bimanual motor skill learning after stroke remains unknown.

Clinical trial registration: https://ichgcp.net/clinical-trials-registry/NCT02308852, identifier: NCT02308852.

Keywords: anodal tDCS; bimanual coordination; motor skill learning; noninvasive brain stimulation (NIBS); primary motor cortex (M1); robotics; stroke.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2022 De Laet, Herman, Riga, Bihin, Regnier, Leeuwerck, Raymackers and Vandermeeren.

Figures

Figure 1

Study design. BBT, box and blocks test; R1/R2, retentions 1 and 2, respectively; new circuit: generalization.

Figure 2

Bimanual tasks on the REAplan®. Upper left (A) General setup of the bimanual version of the REAplan® robot. Note that each hand slides exclusively along one axis and thus controls a different direction of the common cursor (small arrowhead) displayed on the REAplan® screen. The forearms rested in gutters and were strapped. Handles were adapted, if needed. Upper right (B) Four different circuits of identical length and difficulty. Bottom, from left to right: Cursor's displacement with regard to the ideal trajectory defined as the center of the circuit's track (surface = error) (C), simple square used for familiarization (D), and REACHING toward the four targets (E).

Figure 3

Main results. Evolution over time of biSAT (in a.u.), biCO (in a.u.) and biFOP (in N) on the bimanual CIRCUIT task at the group level (bold line: group's mean). B: baseline, T1-T5: bimanual training under sham or real tDCS, after-after30-after-60: evaluation immediately after intervention and 30 and 60 min later, respectively; R1-R2: retention blocks 1 and 2 at 1 week after intervention, respectively; G: generalization block (new CIRCUIT).