W. Geoffrey Wright

Assisted Movement With Enhanced Sensation (AMES): Coupling Motor and Sensory to Remediate Motor Deficits in Chronic Stroke Patients

Background. Conventional methods of rehabilitation in patients with chronic, severe motor impairments after stroke usually do not lessen paresis. Objective. A novel therapeutic approach (assisted movement with enhanced sensation [AMES]) was employed in a medical device phase I clinical trial to reduce paresis and spasticity and, thereby, to improve motor function. Methods. Twenty subjects more than 1 year poststroke with severe motor disability of the upper or lower extremity were studied. A robotic device cycled the ankle or the wrist and fingers at 5°/s through ±17.5° in flexion and extension while the subject assisted this motion. Feedback of the subjects active torque was displayed on a monitor. Simultaneously, 2 vibrators applied a 60 pps stimulus to the tendons of the lengthening muscles, alternating from flexors to extensors as the joint rotation reversed from extension to flexion, respectively. Subjects treated themselves at home for 30 min/day for 6 months. Every other day prior to treatment, the therapy device performed automated tests of strength and joint positioning. Functional testing was performed prior to enrollment, immediately after completing the protocol, and 6 months later. Functional tests included gait and weight distribution (lower extremity subjects only) and the Stroke Impact Scale. Results. Most subjects improved on most tests, and gains were sustained for 6 months in most subjects. No safety problems arose. Conclusion. The AMES strategy appears safe and possibly effective in patients with severe chronic impairments. The mechanism underlying these gains is likely to be multifactorial.

Using virtual reality to augment perception, enhance sensorimotor adaptation, and change our minds

Technological advances that involve human sensorimotor processes can have both intended and unintended effects on the central nervous system (CNS). This mini review focuses on the use of virtual environments (VE) to augment brain functions by enhancing perception, eliciting automatic motor behavior, and inducing sensorimotor adaptation. VE technology is becoming increasingly prevalent in medical rehabilitation, training simulators, gaming, and entertainment. Although these VE applications have often been shown to optimize outcomes, whether it be to speed recovery, reduce training time, or enhance immersion and enjoyment, there are inherent drawbacks to environments that can potentially change sensorimotor calibration. Across numerous VE studies over the years, we have investigated the effects of combining visual and physical motion on perception, motor control, and adaptation. Recent results from our research involving exposure to dynamic passive motion within a visually-depicted VE reveal that short-term exposure to augmented sensorimotor discordance can result in systematic aftereffects that last beyond the exposure period. Whether these adaptations are advantageous or not, remains to be seen. Benefits as well as risks of using VE-driven sensorimotor stimulation to enhance brain processes will be discussed.

Linear vection in virtual environments can be strengthened by discordant inertial input

Visual and gravitoinertial sensory inputs are integrated by the central nervous system to provide a compelling and veridical sense of spatial orientation and motion. Although its known that visual input alone can drive this perception, questions remain as to how vestibular/ proprioceptive (i.e. inertial) inputs integrate with visual input to affect this process. This was investigated further by combining sinusoidal vertical linear oscillation (5 amplitudes between 0m and ±0.8m) with two different virtual visual inputs. Visual scenes were viewed in a large field-of-view head-mounted display (HMD), which depicted an enriched, hi-res, dynamic image of the actual test chamber from the perspective of a subject seated in the linear motion device. The scene either depicted horizontal (±0.7m) or vertical (±0.8m) linear 0.2Hz sinusoidal translation. Horizontal visual motion with vertical inertial motion represents a 90° spatial shift. Vertical visual motion with vertical inertial motion whereby the highest physical point matches the lowest visual point and vice versa represents a 180° temporal shift, i.e. opposite of what one experiences in reality. Inertial-only stimulation without visual input was identified as vertical linear oscillation with accurate reports of acceleration peaks and troughs, but a slight tendency to underestimate amplitude. Visual-only (stationary) stimulation was less compelling than combined visual+inertial conditions. In visual+inertial conditions, visual input dominated the direction of perceived self-motion, however, increasing the inertial amplitude increased how compelling this non-veridical perception was. That is, perceived vertical self-motion was most compelling when inertial stimulation was maximal, despite perceiving “up” when physically “down” and vice versa. Similarly, perceived horizontal self-motion was most compelling when vertical inertial motion was at maximum amplitude. “Cross-talk” between visual and vestibular channels was suggested by reports of small vertical components of perceived self-motion combined with a dominant horizontal component. In conclusion, direction of perceived self-motion was dominated by visual motion, however, compellingness of this illusion was strengthened by increasing discordant inertial input. Thus, spatial mapping of inertial systems may be completely labile, while amplitude coding of the input intensifies the percept.

Interpretation of postural control may change due to data processing techniques.

Postural control is commonly assessed by quantifying center of pressure (CoP) variability during quiet stance. CoP data is traditionally filtered prior to analysis. However, some researchers suggest filtering may lead to undesirable consequences. Further, sampling frequency may also affect CoP analysis, as filtering CoP signals of different sampling frequencies may influence variability metrics. This study examined the influence of sampling frequency and filtering on metrics that index the magnitude and structure of variability in CoP displacement and velocity. Healthy adults (N=8, 27.4±2.6 years) balanced on their right foot for 60s on a force plate. CoP data recorded at 100Hz was then downsampled and/or filtered (2nd order dual-pass 10Hz low-pass Butterworth) to create six different CoP time series for each participant: (1) original, (2) filtered, (3) downsampled to 50Hz, (4) downsampled to 25Hz, (5) downsampled to 50Hz and filtered, and (6) down-sampled to 25Hz and filtered. Data were then analyzed using four common variability metrics (standard deviation [SD], root mean square [RMS], detrended fluctuation analysis α [DFA α], and sample entropy [SampEn]). Data processing techniques did not influence the magnitude of variability (SD and RMS), but did influence the structure of variability (DFA α and SampEn) in CoP displacement. All metrics were influenced by data processing techniques in CoP velocity. Thus, when interpreting changes in CoP variability, one must be careful to identify how much change is driven by the neuromotor system and how much is a function of data processing technique.

Assessing subacute mild traumatic brain injury with a portable virtual reality balance device

Abstract Purpose: Balance impairment is a common sensorimotor symptom in mild traumatic brain injury (mTBI). We designed an affordable, portable virtual reality (VR)-based balance screening device (Virtual Environment TBI Screen [VETS]), which will be validated relative to the Neurocom Sensory Organization Test (SOT) to determine if it can replace commonly used postural assessments. Methods: This preliminary study examines healthy adults (n = 56) and adults with mTBI (n = 11). Participants performed six upright postural tasks on the VETS and the SOT. Analysis of variance was used to determine between-group differences. Pearson’s correlations were used to establish construct validity. Known-groups approach was used to establish classification accuracy. Results: The mTBI cohort performed significantly worse than the healthy cohort on the new device (p = 0.001). The new device has 91.0% accuracy and an ROC curve with a significant area-under-the-curve (AUC = 0.865, p < 0.001). Conditions with dynamic visual stimulation were the most sensitive to health status. The SOT had an 84.8% accuracy and AUC =0.703 (p = 0.034). Conclusions: The new VR-based device is a valid measure for detecting balance impairment following mTBI and can potentially replace more expensive and cumbersome equipment. Assessments that test visual-vestibular processing, such as VETS, increase sensitivity to mTBI-related balance deficits, which can be used to guide rehabilitation. Implications for rehabilitation Emerging technology using virtual reality can be economically integrated into the clinical setting for easy testing of postural control in neurologically impaired populations. Tailoring postural assessments to include tasks that rely on visual and vestibular integration will increase the accuracy of detecting balance impairment following mild traumatic brain injury.

Fractal Gait Patterns Are Retained after Entrainment to a Fractal Stimulus

Previous work has shown that fractal patterns in gait can be altered by entraining to a fractal stimulus. However, little is understood about how long those patterns are retained or which factors may influence stronger entrainment or retention. In experiment one, participants walked on a treadmill for 45 continuous minutes, which was separated into three phases. The first 15 minutes (pre-synchronization phase) consisted of walking without a fractal stimulus, the second 15 minutes consisted of walking while entraining to a fractal visual stimulus (synchronization phase), and the last 15 minutes (post-synchronization phase) consisted of walking without the stimulus to determine if the patterns adopted from the stimulus were retained. Fractal gait patterns were strengthened during the synchronization phase and were retained in the post-synchronization phase. In experiment two, similar methods were used to compare a continuous fractal stimulus to a discrete fractal stimulus to determine which stimulus type led to more persistent fractal gait patterns in the synchronization and post-synchronization (i.e., retention) phases. Both stimulus types led to equally persistent patterns in the synchronization phase, but only the discrete fractal stimulus led to retention of the patterns. The results add to the growing body of literature showing that fractal gait patterns can be manipulated in a predictable manner. Further, our results add to the literature by showing that the newly adopted gait patterns are retained for up to 15 minutes after entrainment and showed that a discrete visual stimulus is a better method to influence retention.

Manual motor control during “virtual” self-motion: Implications for VR rehabilitation

The level of immersion that is induced in an individual can be measured by subjective report, but VE immersion can also affect automatic sensorimotor processes which function below perceptual thresholds. Such sub-threshold effects on central nervous system processing are important to understand for the purposes of shaping VE rehabilitation. This study investigates the effect of dynamic immersive VE on self-motion perception and automatic upper extremity motor response. Subjects viewed either horizontal or vertical sinusoidal linear translation ±1m at 0.25 Hz via a head-mounted display (HMD) while sitting in a stationary motion apparatus. Subjects performed a perceptuomotor task of aligning a handheld object to perceived vertical using their unconstrained arm (i.e. free to move in 6 DOF). Two objects were tested, a joystick and a full glass of water, in counter-balanced order. Results show the majority of subjects perceive self-motion that spatially and temporally agrees with the visually depicted VE motion. This occurs despite the absence of sinusoidally varying changes to gravitoinertial forces, since subjects are not exposed to actual physical motion. Despite only being instructed to orient the handheld object, handheld object kinematics also show automatic motor responses involving object translation. These manual motor responses were dependent on the direction and phase of the visual motion depicted in the VE. Specifically, vertical visual motion induced vertical translation and pitch tilt of the handheld object, while horizontal visual motion induced horizontal translation and roll tilt of the object. Motor responses were significantly greater in subjects who reported compelling self-motion perception. These findings suggest that a representation of net gravitoinertial forces can be derived from the high-fidelity, pictorial and dynamic depth cues visually presented in a VE. Automatic upper extremity manual responses which are controlled by descending central systems and tracts dissociable from lower extremities can be affected by immersion in a VE much like automatic postural behavior has been shown to be. This new evidence supports current efforts to conduct upper extremity rehabilitation in the relative safe and controllable experimental environments that VE technology affords.

Impaired perception of surface tilt in progressive supranuclear palsy.

Introduction Progressive supranuclear palsy (PSP) is characterized by early postural instability and backward falls. The mechanisms underlying backward postural instability in PSP are not understood. The aim of this study was to test the hypothesis that postural instability in PSP is a result of dysfunction in the perception of postural verticality. Methods We gathered posturography data on 12 subjects with PSP to compare with 12 subjects with idiopathic Parkinson’s Disease (PD) and 12 healthy subjects. Objective tests of postural impairment included: dynamic sensory perception tests of gravity and of surface oscillations, postural responses to surface perturbations, the sensory organization test of postural sway under altered sensory conditions and limits of stability in stance. Results Perception of toes up (but not toes down) surface tilt was reduced in subjects with PSP compared to both control subjects (p≤0.001 standing, p≤0.007 seated) and subjects with PD (p≤0.03 standing, p≤0.04 seated). Subjects with PSP, PD and normal controls accurately perceived the direction of gravity when standing on a tilting surface. Unlike PD and control subjects, subjects with PSP exerted less postural corrective torque in response to toes up surface tilts. Discussion Difficulty perceiving backward tilt of the surface or body may account for backward falls and postural impairments in patients with PSP. These observations suggest that abnormal central integration of sensory inputs for perception of body and surface orientation contributes to the pathophysiology of postural instability in PSP.

Development of a Portable Tool for Screening Neuromotor Sequelae From Repetitive Low-Level Blast Exposure

Blast exposure is a prevalent cause of mild traumatic brain injury (mTBI) in military personnel in combat. However, it is more common for a service member to be exposed to a low-level blast (LLB) that does not result in a clinically diagnosable mTBI. Recent research suggests that repetitive LLB exposure can result in symptomology similar to symptoms observed after mTBI. This manuscript reports on the use of an Android-based smartphone application (AccWalker app) to capture changes in neuromotor functioning after blast exposure. Active duty U.S. Navy personnel (N = 59) performed a stepping-in-place task before repetitive LLB exposure (heavy weapons training), and again immediately after, 24 hours after, and 72 to 96 hours after the completion of the training. The AccWalker app revealed that there are changes in neuromotor functioning after LLB exposure (slower self-selected movement pace and increased stride time variability) in participants who experienced neurocognitive decline. These data suggest that neurocognitive and neuromotor decline can occur after repeated LLB exposure.

Using virtual reality to induce cross-axis adaptation of postural control: Implications for rehabilitation

Adaptation of sensorimotor processes has been studied for over a century. However, rigorous experimental approaches require controlling as many variables as possible to study the phenomenon, which limits generalizability. Conversely testing adaptation in an unconstrained ecologically valid situation makes it difficult to identify what parameters affect this process. This study utilizes virtual environments (VE) to create complex, but controlled environments to test visual, vestibular, and sensorimotor adaptation of whole-body posture. Findings show automatic postural processes can be adapted to unusual and discordant sensory environments, suggesting its lability would be advantageous when employing the kind of sensorimotor rehabilitation therapy VE affords.