Motor Imagery Performance through Embodied Digital Twins in a Virtual Reality-Enabled Brain-Computer Interface Environment.

This study introduces an innovative framework for neurological rehabilitation by integrating brain-computer interfaces (BCI) and virtual reality (VR) technologies with the customization of three-dimensional (3D) avatars. Traditional approaches to rehabilitation often fail to fully engage patients, primarily due to their inability to provide a deeply immersive and interactive experience. This research endeavors to fill this gap by utilizing motor imagery (MI) techniques, where participants visualize physical movements without actual execution. This method capitalizes on the brain's neural mechanisms, activating areas involved in movement execution when imagining movements, thereby facilitating the recovery process. The integration of VR's immersive capabilities with the precision of electroencephalography (EEG) to capture and interpret brain activity associated with imagined movements forms the core of this system. Digital Twins in the form of personalized 3D avatars are employed to significantly enhance the sense of immersion within the virtual environment. This heightened sense of embodiment is crucial for effective rehabilitation, aiming to bolster the connection between the patient and their virtual counterpart. By doing so, the system not only aims to improve motor imagery performance but also seeks to provide a more engaging and efficacious rehabilitation experience. Through the real-time application of BCI, the system allows for the direct translation of imagined movements into virtual actions performed by the 3D avatar, offering immediate feedback to the user. This feedback loop is essential for reinforcing the neural pathways involved in motor control and recovery. The ultimate goal of the developed system is to significantly enhance the effectiveness of motor imagery exercises by making them more interactive and responsive to the user's cognitive processes, thereby paving a new path in the field of neurological rehabilitation.

Cortical activation and BCI performance during brief tactile imagery: A comparative study with motor imagery.

Brain-computer interfaces (BCIs) rely heavily on motor imagery (MI) for operation, yet tactile imagery (TI) presents a novel approach that may be advantageous in situations where visual feedback is impractical. The current study aimed to compare the cortical activity and digit classification performance induced by TI and MI to assess the viability of TI for use in BCIs. Twelve right-handed participants engaged in trials of TI and MI, focusing on their left and right index digits. Event-related desynchronization (ERD) in the mu and beta bands was analyzed, and classification accuracy was determined through an artificial neural network (ANN). Comparable ERD patterns were observed in both TI and MI, with significant decreases in ERD during imagery tasks. The ANN demonstrated high classification accuracy, with TI achieving a mean±SD of 79.30 ± 3.91 % and MI achieving 81.10 ± 2.96 %, with no significant difference between the two (p = 0.11). The study found that TI induces substantial ERD comparable to MI and maintains high classification accuracy, supporting its potential as an effective mental strategy for BCIs. This suggests that TI could be a valuable alternative in BCI applications, particularly for individuals unable to rely on visual cues.

Feasibility and usability of a virtual-reality-based sensorimotor activation apparatus for carpal tunnel syndrome patients.

PURPOSE: This study aimed to assess the usability of a virtual reality-assisted sensorimotor activation (VRSMA) apparatus for individual digit rehabilitation. The study had two main objectives: Firstly, to collect preliminary data on the expectations and preferences of patients with carpal tunnel syndrome (CTS) regarding virtual reality (VR) and an apparatus-assisted therapy for their affected digits. Secondly, to evaluate the usability of the VRSMA apparatus that was developed. METHODS: The VRSMA system consists of an apparatus that provides sensory and motor stimulation via a vibratory motor and pressure sensor attached to a button, and a virtual reality-based visual cue provided by texts overlaid on top of a 3D model of a hand. The study involved 10 CTS patients who completed five blocks of VRSMA with their affected hand, with each block corresponding to the five digits. The patients were asked to complete a user expectations questionnaire before experiencing the VRSMA, and a user evaluation questionnaire after completing the VRSMA. Expectations for VRSMA were obtained from the questionnaire results using a House of Quality (HoQ) analysis. RESULTS: In the survey for expectations, participants rated certain attributes as important for a rehabilitation device for CTS, with mean ratings above 4 for attributes such as ease of use, ease of understanding, motivation, and improvement of hand function based on clinical evidence. The level of immersion and an interesting rehabilitation regime received lower ratings, with mean ratings above 3.5. The survey evaluating VRSMA showed that the current prototype was overall satisfactory with a mean rating of 3.9 out of 5. Based on the HoQ matrix, the highest priority for development of the VRSMA was to enhance device comfort and usage time. This was followed by the need to perform more clinical studies to provide evidence of the efficacy of the VRSMA. Other technical characteristics, such as VRSMA content and device reliability, had lower priority scores. CONCLUSION: The current study presents a potential for an individual digit sensorimotor rehabilitation device that is well-liked by CTS patients.

The effect of combining action observation in virtual reality with kinesthetic motor imagery on cortical activity.

Introduction: In the past, various techniques have been used to improve motor imagery (MI), such as immersive virtual-reality (VR) and kinesthetic rehearsal. While electroencephalography (EEG) has been used to study the differences in brain activity between VR-based action observation and kinesthetic motor imagery (KMI), there has been no investigation into their combined effect. Prior research has demonstrated that VR-based action observation can enhance MI by providing both visual information and embodiment, which is the perception of oneself as part of the observed entity. Additionally, KMI has been found to produce similar brain activity to physically performing a task. Therefore, we hypothesized that utilizing VR to offer an immersive visual scenario for action observation while participants performed kinesthetic motor imagery would significantly improve cortical activity related to MI. Methods: In this study, 15 participants (9 male, 6 female) performed kinesthetic motor imagery of three hand tasks (drinking, wrist flexion-extension, and grabbing) both with and without VR-based action observation. Results: Our results indicate that combining VR-based action observation with KMI enhances brain rhythmic patterns and provides better task differentiation compared to KMI without action observation. Discussion: These findings suggest that using VR-based action observation alongside kinesthetic motor imagery can improve motor imagery performance.

Enhanced motor imagery of digits within the same hand via vibrotactile stimulation.

Purpose: The aim of the present study is to evaluate the effect of vibrotactile stimulation prior to repeated complex motor imagery of finger movements using the non-dominant hand on motor imagery (MI) performance. Methods: Ten healthy right-handed adults (4 females and 6 males) participated in the study. The subjects performed motor imagery tasks with and without a brief vibrotactile sensory stimulation prior to performing motor imagery using either their left-hand index, middle, or thumb digits. Mu- and beta-band event-related desynchronization (ERD) at the sensorimotor cortex and an artificial neural network-based digit classification was evaluated. Results: The ERD and digit discrimination results from our study showed that ERD was significantly different between the vibration conditions for the index, middle, and thumb. It was also found that digit classification accuracy with-vibration (mean ± SD = 66.31 ± 3.79%) was significantly higher than without-vibration (mean ± SD = 62.68 ± 6.58%). Conclusion: The results showed that a brief vibration was more effective at improving MI-based brain-computer interface classification of digits within a single limb through increased ERD compared to performing MI without vibrotactile stimulation.

Evaluation of EEG Oscillatory Patterns and Classification of Compound Limb Tactile Imagery.

Objective: The purpose of this study was to investigate the cortical activity and digit classification performance during tactile imagery (TI) of a vibratory stimulus at the index, middle, and thumb digits within the left hand in healthy individuals. Furthermore, the cortical activities and classification performance of the compound TI were compared with similar compound motor imagery (MI) with the same digits as TI in the same subjects. Methods: Twelve healthy right-handed adults with no history of upper limb injury, musculoskeletal condition, or neurological disorder participated in the study. The study evaluated the event-related desynchronization (ERD) response and brain-computer interface (BCI) classification performance on discriminating between the digits in the left-hand during the imagery of vibrotactile stimuli to either the index, middle, or thumb finger pads for TI and while performing a motor activity with the same digits for MI. A supervised machine learning technique was applied to discriminate between the digits within the same given limb for both imagery conditions. Results: Both TI and MI exhibited similar patterns of ERD in the alpha and beta bands at the index, middle, and thumb digits within the left hand. While TI had significantly lower ERD for all three digits in both bands, the classification performance of TI-based BCI (77.74 ± 6.98%) was found to be similar to the MI-based BCI (78.36 ± 5.38%). Conclusions: The results of this study suggest that compound tactile imagery can be a viable alternative to MI for BCI classification. The study contributes to the growing body of evidence supporting the use of TI in BCI applications, and future research can build on this work to explore the potential of TI-based BCI for motor rehabilitation and the control of external devices.

The relationship between shear wave velocity in transverse carpal ligament and carpal tunnel pressure: A finite element analysis.

Elevated carpal tunnel pressure in carpal tunnel syndrome (CTS) patients is one of the major causes of nerve damage but cannot be measured non-invasively. This study proposed to use shear wave velocity (SWV) in the transverse carpal ligament (TCL) to measure the surrounding carpal tunnel pressure. The relationship between the carpal tunnel pressure and the SWV in the TCL was investigated through a subject-specific carpal tunnel finite element model reconstrued by MRI imaging. Parametric analysis was conducted to study the effect of TCL Young's modulus and carpal tunnel pressure on the TCL SWV. The SWV in TCL was found to be strongly dependent on the carpal tunnel pressure and TCL Young's modulus. The calculated SWV ranged from 8.0 m/s to 22.6 m/s under a combination of carpal tunnel pressure (0-200 mmHg) and TCL Young's modulus (1.1-11 MPa). An empirical equation was used to fit the relationship between the SWV in TCL and carpal tunnel pressure, with TCL Young's modulus as a confounding factor. The equation proposed in this study provided an approach to estimate carpal tunnel pressure by measuring the SWV in the TCL for a potential non-invasive diagnosis of CTS and may shed light on the mechanical nerve damage mechanism.

A finite element analysis of the carpal arch with various locations of carpal tunnel release.

Objective: The purpose of this study was to investigate the effects of the location of transverse carpal ligament (TCL) transection on the biomechanical property of the carpal arch structure. It was hypothesized that carpal tunnel release would lead to an increase of the carpal arch compliance (CAC) in a location-dependent manner. Methods: A pseudo-3D finite element model of the volar carpal arch at the distal carpal tunnel was used to simulate arch area change under different intratunnel pressures (0-72 mmHg) after TCL transection at different locations along the transverse direction of the TCL. Results: The CAC of the intact carpal arch was 0.092 mm2/mmHg, and the simulated transections ranging from 8 mm ulnarly to 8 mm radially from the center point of the TCL led to increased CACs that were 2.6-3.7 times of that of the intact carpal arch. The CACs after radial transections were greater than those ulnarly transected carpal arches. Conclusion: The TCL transection in the radial region was biomechanically favorable in reducing carpal tunnel constraint for median nerve decompression.

The Effect of Tactile Imagery Training on Reaction Time in Healthy Participants.

BACKGROUND: Reaction time is an important measure of sensorimotor performance and coordination and has been shown to improve with training. Various training methods have been employed in the past to improve reaction time. Tactile imagery (TI) is a method of mentally simulating a tactile sensation and has been used in brain-computer interface applications. However, it is yet unknown whether TI can have a learning effect and improve reaction time. OBJECTIVE: The purpose of this study was to investigate the effect of TI on reaction time in healthy participants. METHODS: We examined the reaction time to vibratory stimuli before and after a TI training session in an experimental group and compared the change in reaction time post-training with pre-training in the experimental group as well as the reaction time in a control group. A follow-up evaluation of reaction time was also conducted. RESULTS: The results showed that TI training significantly improved reaction time after TI compared with before TI by approximately 25% (pre-TI right-hand mean ± SD: 456.62 ± 124.26 ms, pre-TI left-hand mean ± SD: 448.82 ± 124.50 ms, post-TI right-hand mean ± SD: 340.32 ± 65.59 ms, post-TI left-hand mean ± SD: 335.52 ± 59.01 ms). Furthermore, post-training reaction time showed significant reduction compared with the control group and the improved reaction time had a lasting effect even after four weeks post-training. CONCLUSION: These findings indicate that TI training may serve as an alternate imagery strategy for improving reaction time without the need for physical practice.

The Effects of Subthreshold Vibratory Noise on Cortical Activity During Motor Imagery.

Previous studies have demonstrated that both visual and proprioceptive feedback play vital roles in mental practice of movements. Tactile sensation has been shown to improve with peripheral sensory stimulation via imperceptible vibratory noise by stimulating the sensorimotor cortex. With both proprioception and tactile sensation sharing the same population of posterior parietal neurons encoding within high-level spatial representations, the effect of imperceptible vibratory noise on motor imagery-based brain-computer interface is unknown. The objective of this study was to investigate the effects of this sensory stimulation via imperceptible vibratory noise applied to the index fingertip in improving motor imagery-based brain-computer interface performance. Fifteen healthy adults (nine males and six females) were studied. Each subject performed three motor imagery tasks, namely drinking, grabbing, and flexion-extension of the wrist, with and without sensory stimulation while being presented a rich immersive visual scenario through a virtual reality headset. Results showed that vibratory noise increased event-related desynchronization during motor imagery compared with no vibration. Furthermore, the task classification percentage was higher with vibration when the tasks were discriminated using a machine learning algorithm. In conclusion, subthreshold random frequency vibration affected motor imagery-related event-related desynchronization and improved task classification performance.

Posture dependent factors influence movement variability when reaching to nearby virtual objects.

Reaching movements are subject to noise arising during the sensing, planning and execution phases of movement production, which contributes to movement variability. When vision of the moving hand is available, reach endpoint variability appears to be strongly influenced by internal noise associated with the specification and/or online updating of movement plans in visual coordinates. In contrast, without hand vision, endpoint variability appears more dependent upon movement direction, suggesting a greater influence of execution noise. Given that execution noise acts in part at the muscular level, we hypothesized that reaching variability should depend not only on movement direction but initial arm posture as well. Moreover, given that the effects of execution noise are more apparent when hand vision is unavailable, we reasoned that postural effects would be more evident when visual feedback was withheld. To test these hypotheses, participants planned memory-guided reaching movements to three frontal plane targets using one of two initial arm postures ("adducted" or "abducted"), attained by rotating the arm about the shoulder-hand axis. In this way, variability was examined for two sets of movements that were largely identical in endpoint coordinates but different in joint/muscle-based coordinates. We found that patterns of reaching variability differed in several respects when movements were initiated with different arm postures. These postural effects were evident shortly after movement onset, near the midpoints of the movements, and again at the endpoints. At the endpoints, posture dependent effects interacted with effects of visual feedback to determine some aspects of variability. These results suggest that posture dependent execution noise interacts with feedback control mechanisms and biomechanical factors to determine patterns of reach endpoint variability in 3D space.

The effects of wrist position and radioulnar wrist compression on median nerve longitudinal mobility.

BACKGROUND: Carpal tunnel syndrome is an entrapment neuropathy at the wrist characterized by compromised median nerve mobility. The purpose of this study was to investigate the effect of wrist position on median nerve longitudinal mobility in healthy subjects and the effect of radioulnar wrist compression on the median nerve mobility under non-neutral wrist positions. METHODS: Dynamic B mode ultrasound images captured longitudinal median nerve motion in the carpal tunnel in 10 healthy subjects at wrist neutral position, 30-degree flexion, and 30-degree extension. In each position, RWC of 0, 5, 10, and 15 N were applied. One-way repeated measure analysis of variance (ANOVA), Post-hoc Tukey's tests, and the Friedman Test were used to show the significant differences of median nerve longitudinal mobility at different wrist positions and force conditions. FINDINGS: Median nerve longitudinal mobility was found to be significantly influenced by wrist position (P < 0.05). The mobility under wrist neutral position was 3.02 mm/s, 38% higher than under wrist flexion (2.18 ± 0.60 mm/s), and 32% higher than under wrist extension (2.29 ± 0.43 mm/s). The impaired median nerve mobility was significantly restored under 10 N radioulnar wrist compression (P < 0.05), by 34.4% under wrist flexion (3.03 ± 0.85 mm/s), and 38.9% under wrist extension (3.07 ± 0.79 mm/s). INTERPRETATION: Non-neutral wrist positions compromise median nerve longitudinal mobility, but moderate radioulnar compressive forces are beneficial in the recovery of median nerve longitudinal mobility, and may help to prevent symptoms associated with carpal tunnel syndrome.

Median nerve and carpal arch morphology changes in women with type 2 diabetes: a case-control study.

BACKGROUND: The aim of this study is to investigate the changes in median nerve and transverse carpal ligament (TCL)-formed carpal arch morphology as possible risk factors for median nerve entrapment in women with type 2 diabetes. METHODS: The distal carpal tunnel was imaged using ultrasound in 30 female subjects (15 with type 2 diabetes, 15 controls). The morphological parameters of the median nerve and carpal arch were derived from the ultrasound images. One-way analysis of variance (ANOVA) was used for statistical analysis. RESULTS: Diabetic women had an enlarged median nerve area (p < 0.05), salong with a maller carpal arch size, as indicated by a reduced palmar bowing index of the TCL (p < 0.05), and arch area (p < 0.05) than controls. The distance from the median nerve centroid to the volar boundary of the TCL was reduced in diabetic women (p < 0.05) compared to the controls. CONCLUSIONS: Women with type 2 diabetes have reduced available space for the median nerve within the carpal arch due to the enlarged nerve and reduced arch size, making the median nerve more susceptible to entrapment within the tunnel. The current study shows that presence of diabetes increases the risk of median nerve entrapment in women and requires early detection of symptoms to avoid carpal tunnel syndrome.

Morphological and positional changes of the carpal arch and median nerve associated with wrist deviations.

BACKGROUND: Carpal tunnel and median nerve dynamically change with wrist motion. The purpose of this study was to investigate the morphological changes and positional migration of the carpal arch and median nerve, as well as nerve-arch positional relationship associated with wrist deviation in healthy volunteers. METHODS: Twenty asymptomatic male volunteers performed wrist motion from neutral to deviated positions combining flexion-extension and radioulnar deviation. Ultrasound images of the carpal arch and median nerve at the distal carpal tunnel were collected during wrist motion. Morphological and positional parameters of the carpal arch and median nerve were derived from the ultrasound images. FINDINGS: Carpal arch height, area, and palmar bowing of the transverse carpal ligament (TCL) increased with flexion related wrist motion and decreased with extension related motion (P < 0.05). Arch width increased with radial flexion and decreased with extension and ulnar extension (P < 0.05). Median nerve circularity increased with flexion and radial flexion but decreased with extension, ulnar extension, and ulnar deviation (P < 0.05). Nerve centroid displaced ulnarly with radial deviation, radial flexion, and radial extension and displaced radially with ulnar deviation, ulnar flexion, and ulnar extension (P < 0.05). Nerve centroid displaced in the dorsal direction with flexion and radial flexion, but in the palmar direction with extension (P < 0.05). Nerve-TCL distance increased with flexion related motion and decreased with extension relation motion (P < 0.05). INTERPRETATION: The current study advances our understanding the effect of wrist motion on the carpal tunnel and its contents, which has implications for pathomorphological and pathokinematic changes associated with wrist disorders.

Sex-related differences in carpal arch morphology.

The purpose of this study was to investigate the sex-based differences in the carpal arch morphology. Carpal arch morphology was quantified using palmar bowing and area of the arch formed by the transverse carpal ligament. The carpal arch was imaged at the distal and proximal tunnel levels using ultrasonography in 20 healthy young adults (10 women and 10 men). It was found that females had a smaller carpal arch height compared to men at both distal and proximal levels (p<0.05) and smaller carpal arch width only at the proximal level (p<0.05) but not distally. Palmar bowing index, the carpal arch height to width ratio, was significantly smaller in females at the distal level (p<0.05) but not at the proximal level. Carpal arch cross-sectional area normalized to the wrist cross-sectional area was found to be significantly smaller in females at both tunnel levels compared to men (p<0.05). This study demonstrates that females have a smaller carpal arch compared to men with a reduced palmar bowing distally and a smaller arch area at both tunnel levels. The findings help explain the higher incidence of carpal tunnel syndrome in women as a smaller carpal arch makes the median nerve more vulnerable to compression neuropathy.

Use of imperceptible wrist vibration to modulate sensorimotor cortical activity.

Peripheral sensory stimulation has been used as a method to stimulate the sensorimotor cortex, with applications in neurorehabilitation. To improve delivery modality and usability, a new stimulation method has been developed in which imperceptible random-frequency vibration is applied to the wrist concurrently during hand activity. The objective of this study was to investigate effects of this new sensory stimulation on the sensorimotor cortex. Healthy adults were studied. In a transcranial magnetic stimulation (TMS) study, resting motor threshold, short-interval intracortical inhibition, and intracortical facilitation for the abductor pollicis brevis muscle were compared between vibration on vs. off, while subjects were at rest. In an electroencephalogram (EEG) study, alpha and beta power during rest and event-related desynchronization (ERD) for hand grip were compared between vibration on vs. off. Results showed that vibration decreased EEG power and decreased TMS short-interval intracortical inhibition (i.e., disinhibition) compared with no vibration at rest. Grip-related ERD was also greater during vibration, compared to no vibration. In conclusion, subthreshold random-frequency wrist vibration affected the release of intracortical inhibition and both resting and grip-related sensorimotor cortical activity. Such effects may have implications in rehabilitation.

Feasibility and usability of a wearable orthotic for stroke survivors with hand impairment.

PURPOSE: The concept of a vibrating wristband, to improve dextrous hand function of stroke survivors, was recently proposed with clinical results and is referred to as 'TheraBracelet' in this paper. The purpose of this study was to demonstrate feasibility of a portable, wearable TheraBracelet, and to apply usability evaluation techniques to assess potential demands of TheraBracelet and to identify critical improvement needs of the prototype. METHOD: A prototype was developed with a vibrating element housed in an elastic wristband and connected to a wearable electronics box via a cable. Expectation for TheraBracelet and evaluation of the prototype were obtained from 10 chronic stroke survivors using surveys before and after using the prototype and House of Quality analysis. RESULTS: The survey for expectation showed stroke survivors' willingness to try out TheraBracelet at a low cost. The survey evaluating the prototype showed that the current prototype was overall satisfactory with a mean rating of 3.7 out of 5. The House of Quality analysis revealed that the priority improvement needs for the prototype are to improve clinical knowledge on long-term effectiveness, reduce cost, ease donning/doffing and waterproof. CONCLUSIONS: This study presents a potential for a low-cost wearable hand orthotic likable by stroke survivors. Implications for Rehabilitation Feasibility for a portable wearable wristband-type hand orthotic was demonstrated. The survey showed stroke survivors are willing to try such an orthotic at low cost. The current prototype was rated overall satisfactory by stroke survivors. This study provides a potential for a low-cost wearable hand orthotic likable by stroke survivors.

Usability evaluation of low-cost virtual reality hand and arm rehabilitation games.

The emergence of lower-cost motion tracking devices enables home-based virtual reality rehabilitation activities and increased accessibility to patients. Currently, little documentation on patients' expectations for virtual reality rehabilitation is available. This study surveyed 10 people with stroke for their expectations of virtual reality rehabilitation games. This study also evaluated the usability of three lower-cost virtual reality rehabilitation games using a survey and House of Quality analysis. The games (kitchen, archery, and puzzle) were developed in the laboratory to encourage coordinated finger and arm movements. Lower-cost motion tracking devices, the P5 Glove and Microsoft Kinect, were used to record the movements. People with stroke were found to desire motivating and easy-to-use games with clinical insights and encouragement from therapists. The House of Quality analysis revealed that the games should be improved by obtaining evidence for clinical effectiveness, including clinical feedback regarding improving functional abilities, adapting the games to the user's changing functional ability, and improving usability of the motion-tracking devices. This study reports the expectations of people with stroke for rehabilitation games and usability analysis that can help guide development of future games.

Effect of imperceptible vibratory noise applied to wrist skin on fingertip touch evoked potentials - an EEG study.

Random vibration applied to skin can change the sense of touch. Specifically, low amplitude white-noise vibration can improve fingertip touch perception. In fact, fingertip touch sensation can improve even when imperceptible random vibration is applied to other remote upper extremity areas such as wrist, dorsum of the hand, or forearm. As such, vibration can be used to manipulate sensory feedback and improve dexterity, particularly during neurological rehabilitation. Nonetheless, the neurological bases for remote vibration enhanced sensory feedback are yet poorly understood. This study examined how imperceptible random vibration applied to the wrist changes cortical activity for fingertip sensation. We measured somatosensory evoked potentials to assess peak-to-peak response to light touch of the index fingertip with applied wrist vibration versus without. We observed increased peak-to-peak somatosensory evoked potentials with wrist vibration, especially with increased amplitude of the later component for the somatosensory, motor, and premotor cortex with wrist vibration. These findings corroborate an enhanced cortical-level sensory response motivated by vibration. It is possible that the cortical modulation observed here is the result of the establishment of transient networks for improved perception.