Visual feedback improves movement illusions induced by tendon vibration after chronic stroke

Abstract

Background: Illusion of movement induced by tendon vibration is commonly used in rehabilitation and seems valuable for motor rehabilitation after stroke, by playing a role in cerebral plasticity. The aim was to study if congruent visual cues using Virtual Reality (VR) could enhance the illusion of movement induced by tendon vibration of the wrist among participants with stroke.

Methods: We included 20 chronic stroke participants. They experienced tendon vibration of their wrist (100 Hz, 30 times) inducing illusion of movement. Three VR visual conditions were added to the vibration: a congruent moving virtual hand (Moving condition); a static virtual hand (Static condition); or no virtual hand at all (Hidden condition). The participants evaluated for each visual condition the intensity of the illusory movement using a Likert scale, the sensation of wrist's movement using a degree scale and they answered a questionnaire about their preferred condition.

Results: The Moving condition was significantly superior to the Hidden condition and to the Static condition in terms of illusion of movement (p < 0.001) and the wrist's extension (p < 0.001). There was no significant difference between the Hidden and the Static condition for these 2 criteria. The Moving condition was considered the best one to increase the illusion of movement (in 70% of the participants). Two participants did not feel any illusion of movement.

Conclusions: This study showed the interest of using congruent cues in VR in order to enhance the consistency of the illusion of movement induced by tendon vibration among participants after stroke, regardless of their clinical severity. By stimulating the brain motor areas, this visuo-proprioceptive feedback could be an interesting tool in motor rehabilitation. Record number in Clinical Trials: NCT04130711, registered on October 17th 2019 ( https://ichgcp.net/clinical-trials-registry/NCT04130711?id=NCT04130711&draw=2&rank=1 ).

Keywords: Illusory movement; Rehabilitation; Stroke; Tendon vibration; Virtual reality.

Conflict of interest statement

The Authors declare that there is no conflict of interest.

© 2021. The Author(s).

Figures

Fig. 1

Illustrations of the equipment (example of the positioning of a left arm with a paresis after right stroke). a, b Installation of the vibrator. The forearm was covered with a cloth. c–e Presentation of the 3 virtual visual conditions (respectively Moving, Hidden, Static condition). The arrow is not visible during the experiment. f Protractor to measure the sensation of wrist’s displacement. « -90°» signifies a maximal wrist extension for the left upper limb. The description «values of degree» and « wrist extension, wrist flexion» are not seen by the participant during the trial. g Chronology of the trial

Fig. 2

Pictures of the vibratory device UniVibe™. a Vibration motor. b Vibration device linked to the Arduino® and sound isolated. c Wrist positioning

Fig. 3

Flowchart of the experiment

Fig. 4

Boxplot representing the intensity of illusion of movement. Intensity of illusion of movement experienced in each condition, averaged across all participants (respectively for Moving, Hidden, Static condition). The mean is indicated by dots

Fig. 5

Frequency of sensation of wrist extension. The smoothed histogram depicting the frequency of sensation of wrist movement in each condition averaged across the participants. The zero-degree axis is represented by the vertical line (no illusion). The figure represents the distribution of the values from the protractor, with negative degrees for wrist extension and positive degrees for wrist flexion