Mirror Visual Feedback-Induced Performance Improvement and the Influence of Hand Dominance

Abstract

Mirror visual feedback (MVF) is a promising technique in clinical settings that can be used to augment performance of an untrained limb. Several studies with healthy volunteers and patients using transcranial magnetic stimulation (TMS) or functional magnetic resonance imaging (fMRI) indicate that functional alterations within primary motor cortex (M1) might be one candidate mechanism that could explain MVF-induced changes in behavior. Until now, most studies have used MVF to improve performance of the non-dominant hand (NDH). The question remains if the behavioral effect of MVF differs according to hand dominance. Here, we conducted a study with two groups of young, healthy right-handed volunteers who performed a complex ball-rotation task while receiving MVF of the dominant (n = 16, group 1, MVFDH) or NDH (n = 16, group 2, MVFNDH). We found no significant differences in baseline performance of the untrained hand between groups before MVF was applied. Furthermore, there was no significant difference in the amount of performance improvement between MVFDH and MVFNDH indicating that the outcome of MVF seems not to be influenced by hand dominance. Thus our findings might have important implications in neurorehabilitation suggesting that patients suffering from unilateral motor impairments might benefit from MVF regardless of the dominance of the affected limb.

Keywords: hand dominance; handedness; mirror visual feedback (MVF); motor learning; motor skill learning.

Figure 1

Experimental setup and design. Volunteers performed a complex ball-rotation task with two cork balls. (A) Volunteers in MVF_DH rotated the balls with their non-dominant hand (NDH) in a counterclockwise direction for 1 min (untrained hand pre), followed by a 15 min training period with the dominant hand (DH) in a clockwise direction while mirror visual feedback (MVF) was provided (10 trials of 1 min each with 30 s break in between). After the training phase, the performance of the NDH was retested (untrained hand post). (B) Volunteers in MVF_NDH received the same instructions and conducted the same task just vice versa: MVF-training was performed with the NDH while the DH was assessed before and after MVF (untrained hand pre and post). In both groups, volunteers rotated the balls with the NDH always in a counterclockwise direction and with the DH always in a clockwise direction. (C) During the task, volunteers in both groups were seated in a comfortable chair with their elbows flexed at 90° and with their pronated hands rested on a desk in front of them. While MVF was provided, a mirror was placed in the subject’s midsagittalplane and the performing hand was covered by a wooden barrier to prevent direct view. See text for details.

Figure 2

Effect of MVF on motor performance of the untrained hand. (A) Number of ball-rotations/min of the untrained hand before and after MVF. Note that baseline performance of the untrained hand did not differ between groups. (B) Absolute performance improvement of the untrained hand. Both groups improved their performance with the untrained hand significantly. There was no significant difference in absolute performance improvement of the untrained hand between groups. The plot shows mean values, and whiskers represent standard error (SE) values. ^*P < 0.05; n/s, not significant.