This review covers the rationale, mechanisms, and availability of commercially available virtual environment-based interventions for stroke rehabilitation. It describes interventions for motor, speech, cognitive, and sensory dysfunction. Also discussed are the important features and mechanisms that allow virtual environments to facilitate motor relearning. A common challenge is the inability to translate success in small trials to efficacy in larger populations. The heterogeneity of stroke pathophysiology has been blamed, and experts advocate for the study of multimodal approaches. Therefore, this article also introduces a framework to help define new therapy combinations that may be necessary to address stroke heterogeneity.
Key points
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Virtual environment interventions for motor relearning are popular and well received, but they have a small positive effect over conventional therapy.
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Common consensus is that virtual environment interventions are low risk and are likely beneficial if used as an adjunct to conventional therapy.
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There is a lack of effective and widely available virtual environment treatments for nonmotor deficits such as speech, cognitive function, and sensory dysfunction.
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Future approaches may need to strategically combine multiple interventions to address the multifaceted nature of stroke rehabilitation.
Introduction
Despite our best efforts, stroke continues to be a leading cause of acquired disability throughout the world and is responsible for approximately 102 million disability-adjusted life years annually. Even more concerning to care providers, 66% of the 666,000 new stroke survivors each year may suffer chronic cognitive or physical impairment after 6 months of conventional care.
Evidence for neurologic recovery through cortical reorganization has led to new interventions that try to accelerate functional recovery. One promising approach uses virtual environments (VEs) in the form of video games or therapeutic tasks to train impairments. A definition of VEs is computer-simulated objects that respond to speech or motor input. Many VE therapies for stroke are now commercially available and attract intense interest.
This review focuses on VEs for stroke that are widely available outside of research programs. Those interested the broader academic field can refer to texts such as that by Dietz and Ward. This article begins with the rationale for VE training along with potential mechanisms of action. It groups interventions by their targeted impairments, discusses their efficacy, and concludes with challenges for the field.
Introduction
Despite our best efforts, stroke continues to be a leading cause of acquired disability throughout the world and is responsible for approximately 102 million disability-adjusted life years annually. Even more concerning to care providers, 66% of the 666,000 new stroke survivors each year may suffer chronic cognitive or physical impairment after 6 months of conventional care.
Evidence for neurologic recovery through cortical reorganization has led to new interventions that try to accelerate functional recovery. One promising approach uses virtual environments (VEs) in the form of video games or therapeutic tasks to train impairments. A definition of VEs is computer-simulated objects that respond to speech or motor input. Many VE therapies for stroke are now commercially available and attract intense interest.
This review focuses on VEs for stroke that are widely available outside of research programs. Those interested the broader academic field can refer to texts such as that by Dietz and Ward. This article begins with the rationale for VE training along with potential mechanisms of action. It groups interventions by their targeted impairments, discusses their efficacy, and concludes with challenges for the field.
Features for motor learning in virtual environments
Human training was the first application for VEs beyond their conception as entertainment in the form of stereoscopes and video arcades. Circa 1960, VEs enhanced military flight simulators with visual information that followed pilots’ head movements. Since 1990, the following features associated with promoting neuroplasticity were incorporated into effective VEs for stroke rehabilitation.
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Performance feedback
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Repetitive, goal-oriented tasks with variability covering a range of conditions
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Controlled environment where mistakes have minimal consequences
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Task difficulty scaled to a stroke survivor’s capabilities and skill
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Assist, resist, or repel movement and exaggerate errors
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Focus on targeted skills by reducing contributions from unwanted movements
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Increase motivation and engagement using features from video games
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Facilitate remote social interaction with peers or therapists
Potential mechanisms of action
Effect of Augmented Feedback on Motor Learning
There is sufficient evidence that providing stroke survivors with information about movement quality and task outcome benefits the acquisition and retention of motor skill. Delivering feedback only about task measures leads to immediate improvements in the measures with no gain in movement quality. If feedback is provided only about motor performance (path deviations or compensatory behavior), participants immediately improve both task outcomes and movement quality.
Effect of Virtual Environments on Cortical Networks
Imaging reveals that visuomotor network activation occurs when both able-bodied and stroke survivors view hand motion from a virtual avatar. As the visual quality and sense of immersion increases, so does the recruitment of visuomotor networks, which is maximized when the avatar moves in synchrony with the physical hands. In initial reports, recovery from VE training seems to also demonstrate similar patterns of cortical network change as observed in nonvirtual therapy.
Another method of assessing the state of cortical networks is to infer motor corticospinal excitability using motor-evoked potentials induced by transcranial magnetic stimulation. In stroke survivors, lower conduction time, higher baseline motor-evoked potential amplitude, and greater motor-evoked potential amplitude may benefit motor performance and learning. However, few studies have investigated the effect of VE interventions on corticospinal excitability. One study found that skill learning increased corticospinal excitability but not task performance.
Effect of Immersion on Motor Performance
Motor performance in healthy persons improves with increased VE immersion, but few have investigated the effect of immersion on motor learning after stroke. Levels of VE immersion range from using typical PC monitors all the way to 3-dimensional (3D) goggles. Less immersion reduces movement accuracy, smoothness, and velocity, while increasing task performance time, in the healthy. Stroke survivors performing reaching tasks in an immersive, head-mounted VE with a robotic exoskeleton (versus the real world) had 35% longer completion time, and increased elbow extension and horizontal shoulder abduction.
Impairments targeted by virtual environment interventions
This section focuses on interventions commercially available in the United States.
Upper Extremity Is an Area of Focus
After the initial stroke, 80% of patients experience upper limb impairment. Although 15% may have full spontaneous recovery, after 6 months up to 65% cannot use their hands for activities of daily living. Unsurprisingly, most VE interventions were developed for upper extremity motor training. Recent reviews consistently note that VEs are low risk and may be beneficial for motor relearning when administered as part of a physiotherapy program, but also agree that the quality of current evidence is low and that rigorous comparative studies are needed. Costs range from $100–$200,000.
Proximal movement: shoulder and elbow
Commercial motion-controlled games made for the Wii (Nintendo of America Corp, Redmond, WA), Playstation Move (Sony Computer Entertainment Corp, San Mateo, CA), and Xbox Kinect (Microsoft Corp, Redmond, WA) use gesture-based shoulder-elbow motions as input to various sports simulations or motor coordination games. A recent review found high user acceptance, that 180 minutes per week can be safely tolerated, and no evidence for negative effects on motor function.
However, evidence is weak that they are more beneficial than conventional care. Only 4 small controlled trials exist, 2 of which reported significantly improved outcomes over controls (3 points in Fugl-Myer and 5.5 in the Functional Independence Measure). The current consensus is that commercial games are likely beneficial as a supplement to conventional occupational therapy. However, noteworthy is that they do not train finger or wrist movements, difficulty levels may be unsuitable for the severely impaired, and there is no guard against using compensatory body mechanics.
Rehabilitation-specific VE systems such as IREX (GestureTek Corp, Toronto, ON, Canada), OmniVR (Accelerated Care Plus Corp, Reno, NV), and Jintronix (Jintronix Corp, Seattle, WA) use custom VEs that integrate with 3D cameras. In addition they offer task customization, movement analysis, and usage logs that game consoles cannot offer. However, meta-analysis did not find a significant advantage of clinical systems over game consoles, and no trials have directly compared clinical systems with game consoles.
The largest randomized controlled trial (RCT) using systems of this type used the Virtual Reality Rehabilitation System (EU only; Khymeia Group Ltd, Noventa Padovana, Italy) on 376 stroke survivors (<12 months after stroke) for 40 sessions of 2 hours (1 hour conventional care, 1 hour VE) over 4 weeks, and found a significant effect size of 2.5 ± 0.5 points (4.9 ± 0.9 for those 3–12 months poststroke) for the Fugl-Meyer over controls that had conventional therapy.
InMotion ARM (Interactive Motion Technologies Corp, Watertown, MA) is a robot that guides participants toward targets as they move its handle (like a computer mouse) in reaching tasks and games. A multicenter trial for those less than 6 months poststroke showed that 36 hours of robot therapy over 12 weeks significantly increased the Fugl-Myer by 2 points over usual care, which was not clinically meaningful. Other measures were no better than usual care or dose-matched therapy. Both groups improved, but a follow-up study questioned the robot’s cost-effectiveness given a $5000 premium per participant.
Armeo (Hocoma Inc, Norwell, MA) Power, Spring, and Boom are exoskeletons that allow for assisted 3D arm movement in virtual tasks and games. Power uses motors to guide the arm, Spring uses passive springs to reduce arm movement effort, and Boom suspends the arm against gravity. Patients use Power first, then Spring, then Boom as they regain movement, and require less assistance for virtual task practice, although this progression has not yet been tested in clinical trials. A multisite RCT using Power on 77 chronic stroke survivors for 24 sessions of 45 minutes over 8 weeks found a significant effect of 0.78 points on the Fugl-Meyer compared with conventional care. An uncontrolled trial of Spring on chronic stroke (N = 23) for 36 hours over 12 weeks found a 5-point gain in Fugl-Myer and no change in secondary functional measures.
Distal movement: hand, wrist, and fingers
Music Glove (Flint Rehabilitation Devices LLC, Irvine, CA) trains finger motion by wearing a sensor glove and touching the thumb to the other fingertips to play musical notes. A single-blinded crossover trial in 12 moderately impaired chronic stroke survivors (3 treatments, each for 6 hours over 2 weeks) showed a significant gain of 3.2 blocks on the Box and Blocks Test versus conventional care, but no gain over the game with an isometric force sensor that did not require finger motion.
HandTutor (MediTouch Ltd, Netanya, Israel) uses a sensor glove to control therapy games by finger or wrist flexion/extension. A controlled trial treated 31 chronic subacute (<4 months poststroke) participants by adding 20 to 30 minutes of VE training (experiment) or conventional care (control) to usual care. Results showed significant effects for primary outcomes, but were not sustained at 10 days’ follow-up.
Amadeo (TyroMotion GmbH, Graz, Austria) is a hand exoskeleton that assists individual finger movement during VE training, but requires the arm to be strapped to a fixed base. An RCT with 20 acute inpatient stroke survivors had 20 treatment sessions of 40 minutes each over 4 weeks added to standard care (3 hours per day). Both usual care and robot groups had significant gains (end and 3-month follow-up), but no group effects were found.
Gait Training with Virtual Environments Have Limited Effect
Lower extremity impairment affects 75% of all stroke survivors, and only 15% regain full recovery. Up to 25% will require assistive aids to walk for the rest of their lives. A meta-analysis of 7 RCTs found that VE groups improved gait speed by 0.17 m/s over placebo groups and 0.15 m/s over non-VE usual walking therapy. Though promising, most studies used custom systems, and the same amount of evidence is not available for commercial systems costing $200,000 to $1 million.
LOKOMAT (Hokoma Inc) is a lower extremity exoskeleton for body-weight supported treadmill training, and can be equipped with a computer monitor for use with VE tasks to simulate walking and leg motion training. No studies examined the effect of adding VEs to this system for stroke rehabilitation, but an RCT in children with various neurologic impairments found that a soccer ball-kicking simulation increased motivation, but did not result in greater joint torques.
Motek Medical BV (Amsterdam, the Netherlands) has treadmill systems that are used with wall-sized computer projection screens for immersive VE gait training. CAREN is the most immersive, with a treadmill that moves in 6° of freedom, whereas GRAIL and V-Gait are split-belt treadmills with no moving bases. One study found that adding a VE led to treadmill walking mechanics that were closer to the over-ground condition, but the differences in the VE condition were clinically negligible. No controlled studies for stroke exist on the CAREN system, but case studies used artificially slow optical flow to elicit faster walking.
Balance Interventions Comparable with Conventional Care
Many VE balance interventions have demonstrated positive effects, but they do not exceed controls treated with conventional care. These interventions use a wide range of devices, including motion video games, Xbox Kinect, treadmills, and reaching tasks. Many studies used commercial games for the Wii Fit balance board, which is a force plate accessory ($100; Nintendo Corp). The games (skiing, hula-hooping, and yoga) are controlled by body-weight shifting and were shown to be feasible for both inpatient and home use. Although these VE methods may not be more effective than conventional care, they have been shown to reduce therapist costs without sacrificing efficacy if prescribed appropriately for home use.
Cognitive Rehabilitation Interventions Are Lacking
The efficacy of VEs for cognitive rehabilitation is a weak point in the literature, with few controlled trials and even fewer commercial interventions. Those that exist cost $150 to $850. RehaCom (Hasomed GmbH, Berlin, Germany) PC software trains attention (alertness, vigilance, visual-spatial, selective, and divided), memory, executive functions, and visuomotor skills. A double-blind RCT on 36 stroke survivors (<6 months poststroke) showed significantly improved working memory and word fluency over conventional therapy after nine 30-minute sessions.
“Brain games” are popular in the consumer market, but the cognitive training designed for unimpaired individuals may be unsuitable for neurologic injury. Lumosity (Lumos Labs Corp, San Francisco, CA) is a Web site that trains cognitive functions such as memory, processing speed, attention, and problem solving. Although training transfers to long-term function in healthy adults, an 8-week uncontrolled trial on 5 stroke survivors (>6 months poststroke) found that 3 of the participants completed less than half of 40 self-administered home sessions of 30 minutes, and 2 did none of them. Reasons cited included fatigue and difficulty responding within the allotted time for certain tasks.
Speech Rehabilitation Intervention Options Are Few
Speech therapy VEs are also lacking in evidence from controlled trials, but have consistently positive case series and cost less than $1000. AphasiaScripts (Rehabilitation Institute of Chicago, Chicago, IL) uses virtual avatars for script practice. The avatar’s mouth demonstrates proper speech articulation while it converses to the patient using predefined scripts (no speech recognition). An uncontrolled trial of 20 chronic, aphasic stroke survivors showed a clinically significant decrease of 6.67 points in Communication Difficulty of the Burden of Stroke Scale after 9 weeks of home intervention for 30 minutes per day.
MossTalk Words 2 (Moss Rehabilitation Research Institute, Philadelphia, PA) is PC software that trains single word production using virtual flash cards, and provides performance feedback of pronunciation accuracy using voice recognition. Four case studies spanning 17 stroke survivors all reported that 12 to 20 sessions lasting 1 hour improved untrained object-naming ability when session frequency was at least 3 to 4 per week.
StepByStep (Steps Consulting Ltd, Acton Turville, UK) is also a flash-card–like program, but has prerecorded video of therapists pronouncing the words. It also can train spelling and sentence production, but does not have speech recognition. A single-blind controlled trial of 34 chronic stroke survivors compared 5 months of the intervention (20 minutes, 3 days per week) against no therapy. The intervention group had 19.8% greater untrained object-naming accuracy (10% was clinically significant) that did not persist at 3 months’ follow-up.
Spatial Neglect Is an Area of Need
VEs have been developed for assessing hemispatial neglect that may be more sensitive than manual methods, but there are no widely available VE-specific interventions. One uncontrolled study demonstrated short-term improvement of far-field neglect in 6 stroke survivors (<3 months poststroke) by using a virtual reaching task with the patient’s hands altered to appear in the field of neglect. Others used motor training to treat neglect with the rationale of providing arousal and attention to the neglected limb. An unblinded RCT of 24 stroke survivors (<1 month poststroke) compared reaching tasks using IREX with dose-matched conventional therapy. After 5 weeks of therapy for 30 minutes per day, 5 days per week, the VE group reported greater effect in comparison with controls.
Proprioception and Sensory Deficits Are Gaining Attention
Between 17% and 50% of stroke survivors experience impaired proprioception or sensation, but there are few interventions available, as treatments are passive and VEs are only used to assess deficits. VEs revealed that motor recovery is strongly associated with the return of proprioception. One uncontrolled study (N = 7, >1 year post stroke) showed that recovery of proprioception may be facilitated by a virtual reaching task with a custom-built planar robot providing guidance for five 1-hour sessions over 2 weeks. The robot used force pulses to guide arms toward target elbow angles. All participants showed gains in perceptual acuity, but 3 of the more impaired participants did not have sustained effects at follow-up.
Sensory deficits occur in 50% of stroke survivors, but few treatments exist and no VE interventions have been published. Evidence is lacking for treatments that use electrical cutaneous stimulation, and discrimination task training has little effect.
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