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We have previously shown that healthy subjects can transfer coordination skills to the unpracticed hand by performing a unimanual task with the other hand and visualizing a bimanual action using a game-like interactive system. However, whether this system could be used to transfer coordination skills to the paretic hand after stroke and its underlying neural mechanism remain unknown. Here, using a game-like interactive system for visualization during physical practice in an immersive virtual reality environment, we examined coordination skill improvement in the unpracticed/paretic hand after training in 10 healthy subjects and 13 chronic and sub-acute stroke patients. The bimanual movement task was defined as simultaneously drawing non-symmetric three-sided squares (e.g., U and C), while the training strategy was performing a unimanual task with the right/nonparetic hand and visualizing a bimanual action. We found large decreases in the intra-hand temporal and spatial measures for movement in the unpracticed/paretic hand after training. Furthermore, a substantial reduction in the inter-hand temporal and spatial interference was observed after training. Additionally, we examined the related cortical network evolution using EEG in both the healthy subjects and stroke patients. Our studies show that the cortical network became more efficient after training in the healthy subjects and stroke patients. These results demonstrate that our proposed method could contribute to the transference of coordination skill to the paretic/unpracticed hand by promoting the efficiency of cortical networks.

Background The transfer of the behaviors of a human’s upper limbs to an avatar is widely used in the field of virtual reality rehabilitation. To perform the transfer, movement tracking technology is required. Traditionally, wearable tracking devices are used for tracking; however, these devices are expensive and cumbersome. Recently, non-wearable upper-limb tracking solutions have been proposed, which are less expensive and more comfortable. However, most products cannot track the upper limbs, including the arms and all the fingers at the same time, which limits the limb parts for tracking in a virtual environment and may lead to a limited rehabilitation effect. Methods In this paper, a novel virtual reality rehabilitation system (VRRS) was developed for upper-limb rehabilitation. The VRRS could track the motion of both upper limbs, integrate fine finger motion and the range of motion of the entire arm and map the motion to an avatar. To test the performance of VRRS, two experiments were designed. In the first experiment, we investigated the effect of VRRS on virtual body ownership, agency and location of the body and usability in 8 healthy participants by comparing it with a partial upper-limb tracking method based on a Leap Motion controller (LP) in the same virtual environments. In the second experiment, we examined the feasibility of VRRS in upper-limb rehabilitation with 27 stroke patients. Results VRRS improved the users’ senses of body ownership, agency, and location of the body. The users preferred using the VRRS to using the LP. In addition, we found that although the upper limb motor function of patients from all groups was improved, the difference between the FM scores tested on the first day and the last day of the experimental group was more significant than that of the control groups. Conclusions A VRRS with motion tracking of the upper limbs and avatar control including the arms and all the fingers was developed. It resulted in an improved user experience of embodiment and effectively improved the effects of upper limb rehabilitation in stroke patients. Trial registration The study was registered at the First Affiliated Hospital of Jinan University Identifier: KY-2020–036; Date of registration: June 01, 2020.

Backgrounds: Transferring behaviors of a human’s upper-limbs to an avatar is widely used in the field of virtual reality rehabilitation. To realize the transfer, movement tracking technology is required. Traditionally, wearable tracking devices are used to do the tracking, however the devices are expensive and cumbersome. Recently, non-wearable upper-limb tracking solutions are proposed, which are cheaper and more comfortable to interact. But most of the existing products cannot track full upper-limbs including both the arms and all the fingers, which limits the motion paradigm and further may lead to limited rehabilitation effect. Methods: In this paper, a novel method was first proposed for full avatar’s upper-limb control which integrates the fine finger motion and the arm wide range motion. Then, based on the method, a Virtual Reality Rehabilitation System (VRRS) was developed for upper-limb rehabilitation. To test the performance of VRRS, two experiments were designed. First, in order to investigate the effect of VRRS on virtual body ownership, agency, location of the body and usability, we compared it with the partial upper-limb tracking method based on Leap Motion controller (LP) in same virtual environments. Then, to study the feasibility of VRRS in rehabilitation, we recruited 16 stroke patients and split them into two groups: the experimental group and the control group. Each group consisted 8 patients, with and without employing VRRS respectively.Results: The control of full avatar’s upper-limbs improved the users’ senses on body ownership, agency and location of the body. The users preferred to use VRRS. In addition, although the upper-limb motor function of patients from both groups were improved, the difference between the FM scores tested on the first day and the last day of the experimental group was more significant than that of the control group. Conclusions: VRRS based on the proposed method for full avatar’s upper-limbs control was developed, which improved the user experience on embodiment and effectively improved the rehabilitation effect for upper-limbs of stroke patients.Trial registration:The study was registered at the First Affiliated Hospital of Jinan University Identifier: KY-2020-036; Date of registration - June 01, 2020.