Limited Add-On Effects of Unilateral and Bilateral Transcranial Direct Current Stimulation on Visuo-Motor Grip Force Tracking Task Training Outcome in Chronic Stroke. A Randomized Controlled Trial

Abstract

Background: This randomized controlled trial investigated if uni- and bihemispheric transcranial direct current stimulation (tDCS) of the motor cortex can enhance the effects of visuo-motor grip force tracking task training and transfer to clinical assessments of upper extremity motor function. Methods: In a randomized, double-blind, sham-controlled trial, 40 chronic stroke patients underwent 5 days of visuo-motor grip force tracking task training of the paretic hand with either unilateral or bilateral (N = 15/group) or placebo tDCS (N = 10). Immediate and long-term (3 months) effects on training outcome and motor recovery (Upper Extremity Fugl-Meyer, UE-FM, Wolf Motor Function Test, and WMFT) were investigated. Results: Trained task performance significantly improved independently of tDCS in a curvilinear fashion. In the anodal stimulation group UE-FM scores were higher than in the sham group at day 5 (adjusted mean difference: 2.6, 95%CI: 0.6-4.5, p = 0.010) and at 3 months follow up (adjusted mean difference: 2.8, 95%CI: 0.8-4.7, p = 0.006). Neither training alone, nor the combination of training and tDCS improved WMFT performance. Conclusions: Visuo-motor grip force tracking task training can facilitate recovery of upper extremity function. Only minimal add-on effects of anodal but not dual tDCS were observed. Clinical Trial Registration: https://ichgcp.net/clinical-trials-registry/NCT01969097&cntry=&state=&city=&dist=, identifier: NCT01969097, retrospectively registered on 25/10/2013.

Keywords: chronic stroke; hand function; motor function; motor rehabilitation; tDCS.

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 © 2021 Taud, Lindenberg, Darkow, Wevers, Höfflin, Grittner, Meinzer and Flöel.

Figures

Figure 1

Study flow chart. UE-FM, Upper Extremity Fugl-Meyer; WMFT, Wolf Motor Function Test; tDCS, transcranial direct current stimulation.

Figure 2

Experimental set-up. (A) The Grass® Force Displacement Transducer FT10, the sling to measure the applied strength and the grip board. (B) Shows a left hand grasping the wooden grip while the thumb is placed in the sling connected to the Force Displacement Transducer. (C) Illustrates the overall set-up with the dual tDCS montage.

Figure 3

A typical trial run. This figure shows a typical trial where the participant did not apply enough force. The y-axis represents force, the x-axis time. The three horizontal lines represent, from top to bottom, 40, 35, and 30% of the individual maximum force output. The red curved line represents the applied force by the participant. The highest point of the red line lies beneath 30%. Hence, this is a “miss.”

Figure 4

UE-FM assessment. The graphs depict the adjusted mean UE-FM score for each group at post-assessment and follow-up period based on the linear mixed model. Vertical bars represent model based 95% confidence intervals.

Figure 5

Learning curve in the visuo-motor grip force tracking task training task. The graph depicts the mean number of hits per block for each group across the training and follow-up period based on the linear mixed model. Vertical bars represent model based 95% confidence intervals.

Figure 6

WMFT assessment. The graphs depict the mean WMFT completion time for each group across the training and follow-up period based on the linear mixed model. Vertical bars represent model based 95% confidence intervals.