Localizing EEG Recordings Associated With a Balance Threat During Unexpected Postural Translations in Young and Elderly Adults.

Balance perturbations are accompanied by global cortical activation that increases in magnitude when postural perturbations are unexpected, potentially due to the addition of a startle response. A specific site for best recording the response to unexpected destabilization has not been identified. We hypothesize that a single sensor located near to subcortical brainstem mechanisms could serve as a marker for the response to unpredictable postural events. Twenty healthy young (20.8 ± 2.9 yrs) and 20 healthy elder (71.7 ± 4.2 yrs) adults stood upright on a dynamic platform with eyes open. Platform translations (20 cm at 100 cm/s) were delivered in the posterior (29 trials) and anterior (5 catch trials) directions. Active EEG electrodes were located at Fz and Cz and bilaterally on the mastoids. Following platform acceleration onset, 300 ms of EEG activity from each trial was detrended, baseline-corrected, and normalized to the first trial. Average Root-Mean-Square (RMS) values across "unpredictable" and "predictable" events were computed for each channel. EEG RMS responses were significantly greater with unpredictable than predictable disturbances: Cz ( [Formula: see text]), Fz ( [Formula: see text]), and mastoid ( [Formula: see text]). EEG RMS responses were also significantly greater in elderly than young adults at Cz ( [Formula: see text]) and mastoid ( [Formula: see text]). A significant effect of sex in the responses at the mastoid sensors ( [Formula: see text]) revealed that elderly male adults were principally responsible for the age effect. These results confirm that the cortical activity resulting from an unexpected postural disturbance could be portrayed by a single sensor located over the mastoid bone in both young and elderly adults.

Electrodermal and postural responses in dizzy adults: Diagnostic indicators of vestibular migraine.

INTRODUCTION: No reliable biometric measurement of vestibular involvement with migraine is currently available. OBJECTIVE: Measures of autonomic nervous system and postural responses could serve as quantifiable indicators of vestibular involvement with migraine. METHODS: A convenience sample of 22 young healthy adults (34±9 years old) and 23 young adults (34±8 years old) diagnosed with vestibular migraine (VM) participated. A rod and frame test and clinical outcome measures of dizziness and mobility were administered. Participants stood on foam while viewing two dynamic virtual environments. Trunk acceleration in three planes and electrodermal activity (EDA) were assessed with wearable sensors. Linear mixed models were used to examine magnitude and smoothness of trunk acceleration and tonic and phasic EDA. A Welch's t-test and associations between measures were assessed with a Pearson Correlation Coefficient. Effect sizes of group mean differences were calculated using Cohen's d. RESULTS: Visual dependence was present in 83% of the VM population. Individuals with VM exhibited lower baseline EDA (t(4.17) = -7.2, p = 0.001) and greater normalized trunk accelerations in the vertical (t(42.5) = 2.861, p = 0.006) and medial (t(46.6) = 2.65, p = 0.01) planes than healthy participants. Tonic EDA activity increased significantly across the period of the trial (F (1,417) = 23.31, p = 0.001) in the VM group. Significant associations appeared between vertical trunk acceleration and EDA, Dizziness Handicap Inventory, and Activities of Balance Confidence tools. CONCLUSIONS: Higher tonic EDA activity in healthy adults results in more accurate postural reactions. Results support the supposition that EDA activity and postural acceleration are significantly different between VM and healthy individuals when accommodating for postural instability and visual-vestibular conflict.

The effects of visual context on visual-vestibular mismatch revealed by electrodermal and postural response measures.

BACKGROUND: No objective criteria exist for diagnosis and treatment of visual-vestibular mismatch (VVM). OBJECTIVE: To determine whether measures of electrodermal activity (EDA) and trunk acceleration will identify VVM when exposed to visual-vestibular conflict. METHODS: A modified VVM questionnaire identified the presence of VVM (+ VVM) in 13 of 23 young adults (34 ± 8 years) diagnosed with vestibular migraine. Rod and frame tests and outcome measures for dizziness and mobility were administered. Participants stood on foam while viewing two immersive virtual environments. Trunk acceleration in three planes and electrodermal activity (EDA) were assessed with wearable sensors. Linear mixed effect (LME) models were used to examine magnitude and smoothness of trunk acceleration and tonic and phasic EDA. Welch's t-test and associations between measures were assessed with a Pearson Correlation Coefficient. Effect sizes of group mean differences were calculated. RESULTS: Greater than 80% of all participants were visually dependent. Outcome measures were significantly poorer in the + VVM group: tonic EDA was lower (p < 0.001) and phasic EDA higher (p < 0.001). Postural accelerations varied across groups; LME models indicated a relationship between visual context, postural, and ANS responses in the + VVM group. CONCLUSIONS: Lower tonic EDA with + VVM suggests canal-otolith dysfunction. The positive association between vertical acceleration, tonic EDA, and visual dependence suggests that increased vertical segmental adjustments are used to compensate. Visual context of the spatial environment emerged as an important control variable when testing or treating VVM.

Evolution of postural control assessment: From dynamic posturography to virtual reality.

During the early years of spaceflight it was documented that astronauts were impaired and incapacitated upon return to earth. Computerized Dynamic Posturography (CDP) was devised to investigate and quantify this deficit, and eventually progressed into a clinical assessment tool. The current sprouting of virtual reality (VR) technologies has allowed for the development of an alternative approach that could be more informative. Many low-cost VR systems (including desktop gaming programs designed for rehabilitation) are now available. Continued improvements in this technology indicate a high probability that VR will become an integral component of posturography by replacing present mechanical CDP techniques. We researched the relevant literature to evaluate the strengths and weaknesses of CDP using the Equitest (Neurocom International; Clackamas USA), and the added benefits of incorporating VR to help clinicians assess the complex task of balance maintenance. VR is capable of manipulating task and environmental demands in order to assess functional postural behavior. VR is also a useful tool for clinical testing of postural disorders resulting from sensory mismatch. Although posturography is still a useful clinical tool, VR provides an inherent conflict between the visual and vestibular senses and can elevate the effectiveness of CDP for both assessment and intervention. We conclude that, when initially developed, CDP was innovative and ahead of its time. However, with the advent of VR, we have a chance to modernize CDP and enhance its value as a clinical instrument.

The Untapped Potential of Virtual Reality in Rehabilitation of Balance and Gait in Neurological Disorders.

Dynamic systems theory transformed our understanding of motor control by recognizing the continual interaction between the organism and the environment. Movement could no longer be visualized simply as a response to a pattern of stimuli or as a demonstration of prior intent; movement is context dependent and is continuously reshaped by the ongoing dynamics of the world around us. Virtual reality is one methodological variable that allows us to control and manipulate that environmental context. A large body of literature exists to support the impact of visual flow, visual conditions, and visual perception on the planning and execution of movement. In rehabilitative practice, however, this technology has been employed mostly as a tool for motivation and enjoyment of physical exercise. The opportunity to modulate motor behavior through the parameters of the virtual world is often ignored in practice. In this article we present the results of experiments from our laboratories and from others demonstrating that presenting particular characteristics of the virtual world through different sensory modalities will modify balance and locomotor behavior. We will discuss how movement in the virtual world opens a window into the motor planning processes and informs us about the relative weighting of visual and somatosensory signals. Finally, we discuss how these findings should influence future treatment design.

Visual-vestibular mismatch correlates with headache.

BACKGROUND: Dizziness affects 20-30%of the general population. A subgroup of dizzy patients with chronic migraine suffers vertigo implying that the migraine has a vestibular component. Vestibular migraine remains a diagnosis of exclusion based on history. OBJECTIVE: A link between headaches and dizziness suggests that these individuals would demonstrate dizziness and instability in complex, dynamic visual environments as a result of an inability to correctly process conflicting visual and vestibular signals. METHODS: A convenience sample of 74 patients (22 men and 52 women; average age 56.2 years) who presented with complaints of dizziness participated. Effects of Visual-Vestibular Mismatch (VVM) were measured using a modified VVM questionnaire. Visual dependence was measured as the error to subjective visual vertical using a computerized Rod and Frame test. RESULTS: Forty-two participants (56.8%) tested positive for VVM. Of these, 68.9%were patients with concomitant complaints of headaches. Visual dependence was present in 41.5%of all patients but showed no significant correlation with headache. 22.2%of patients had visual dependence and complained of headaches. CONCLUSIONS: These results demonstrate that sensory reweighting occurs in patients experiencing dizziness and headache, supports the role of vestibular involvement in this disorder, and provides future direction for novel interventions.

Influence of Visual Dependence on Inter-Segmental Coordination during Upright Stance in Cerebral Palsy.

The presence of visual dependence as an influential factor on the development of functional stability in ambulatory individuals with cerebral palsy (CP) was studied in 22 adults with spastic bilateral CP, 11 of whom were considered visually dependent, and 18 healthy adults. Participants stood upright during pitch plane disturbances of the visual field and support surface. Intersegmental coordination behaviors were assessed by fitting trajectories of adjacent body segments to an ellipse. Mixed-model repeated measures ANOVAs were performed on ellipse orientation angle and area. Dissimilar stabilizing strategies adopted by the two groups with CP imply that visual dependence impacts postural control. Postural reorganization in response to visual flow in all groups indicates that we cannot ignore perceptual aspects of postural control when designing therapeutic interventions.

Tracking the evolution of virtual reality applications to rehabilitation as a field of study.

BACKGROUND: Application of virtual reality (VR) to rehabilitation is relatively recent with clinical implementation very rapidly following technological advancement and scientific discovery. Implementation is often so rapid that demonstrating intervention efficacy and establishing research priorities is more reactive than proactive. This study used analytical tools from information science to examine whether application of VR to rehabilitation has evolved as a distinct field of research or is primarily a methodology in core disciplines such as biomedical engineering, medicine and psychology. METHODS: The analysis was performed in three-stages: 1) a bibliographic search in the ISI Web of Science database created an initial corpus of publications, 2) the corpus was refined through topic modeling, and 3) themes dominating the corpus from the refined search results were identified by topic modeling and network analytics. This was applied separately to each of three time periods: 1996 to 2005 (418 publications), 2006 to 2014 (1454 publications), and 2015 to mid-2018 (1269 publications). RESULTS: Publication rates have continuously increased across time periods with principal topics shifting from an emphasis on computer science and psychology to rehabilitation and public health. No terminology specific to the field of VR-based rehabilitation emerged; rather a range of central concepts including "virtual reality", "virtual gaming", "virtual environments", "simulated environments" continue to be used. Communities engaged in research or clinical application of VR form assemblages distinguished by a focus on physical or psychological rehabilitation; these appear to be weakly linked through tele-rehabilitation. CONCLUSIONS: Varying terms exemplify the main corpus of VR-based rehabilitation and terms are not consistent across the many scientific domains. Numerous distinguishable areas of research and clinical foci (e.g., Tele-rehabilitation, Gait & Balance, Cognitive Rehabilitation, Gaming) define the agenda. We conclude that VR-based rehabilitation consists of a network of scientific communities with a shared interest in the methodology rather than a directed and focused research field. An interlinked team approach is important to maintain scientific rigor and technological validity within this diverse group. Future studies should examine how these interdisciplinary communities individually define themselves with the goals of gathering knowledge and working collectively toward disseminating information essential to associated research communities.

Visual dependence affects postural sway responses to continuous visual field motion in individuals with cerebral palsy.

The current study aimed to explore the impact of visual dependence on sensorimotor coupling of postural sway and visual motion in adults and teens with spastic cerebral palsy (CP). We hypothesized that individuals with CP would exhibit greater magnitudes of sway than healthy individuals, and the presence of visual dependence (VD) would produce instability in the direction of visual motion. Participants stood in a virtual environment in which the visual scene remained static or continuously rotated 30 degree/second in pitch-up or pitch-down. Increased center of pressure and center of mass responses were observed in the direction of visual scene motion in those with CP. Those with VD exhibited reduced frequency responses in anterior-posterior direction than those who were visually independent. VD suggests deficient sensorimotor integration that could contribute to postural instability and reduced motor function. Individuals with CP who are visually dependent may benefit from more sensory focused rehabilitation strategies. ABBREVIATIONS: AP, anterior-posterior; CP, cerebral palsy; COM, center of mass; COP, center of pressure; MDF, median frequency; ML, mediolateral; PD, pitch down (nose down) rotation; PU, pitch up (nose up) rotation; RFT, rod and frame test; RMS, root mean square; SLP, slope of the fitted line; TD, typical development; VD, visual dependence; VI, visual independence; VOR, vestibulo-ocular reflex; VPI, visual perceptual impairment.

The quest to apply VR technology to rehabilitation: tribulations and treasures.

The papers that follow stem from a symposium presented at the International Society for Posture and Gait Research (ISPGR) in Seville, Spain, in July 2015. Four speakers were charged with presenting their methods of applying virtual reality (VR) technology to obtain meaningful rehabilitation outcomes. The symposium aims to explore characteristics of VR that modify mechanisms supporting motor relearning. Common impairments in posture and gait that can be modulated within virtual environments by employing motor learning concepts, including sensory augmentation and repetition, were examined. Critical overviews of VR applications that address different therapeutic objectives for improving posture and gait in individuals with neurological insult or injury were presented. A further goal was to identify approaches and efforts to bridge the gap between knowledge generation from research and knowledge uptake in clinical practice. Specific objectives of this symposium were that participants be able to: 1) identify benefits and limitations of selecting VR as an intervention tool; 2) discuss how VR relates to principles for motor relearning following neurological insult or injury; and 3) identify areas and methods for future translation of VR technology in clinical and home-based settings. Our symposium concluded that the application of VR technology in assessment, treatment, and research has yielded promising results in transferring learned cognitive and motor skills to more natural environments. VR permits the user to interact with a multidimensional and multisensory environment in real time, and offers the opportunity to provide both standardized and individualized interventions while monitoring behavior.

Posturography using the Wii Balance Board™: A feasibility study with healthy adults and adults post-stroke.

BACKGROUND: Posturography systems that incorporate force platforms are considered to assess balance and postural control with greater sensitivity and objectivity than conventional clinical tests. The Wii Balance Board (WBB) system has been shown to have similar performance characteristics as other force platforms, but with lower cost and size. OBJECTIVES: To determine the validity and reliability of a freely available WBB-based posturography system that combined the WBB with several traditional balance assessments, and to assess the performance of a cohort of stroke individuals with respect to healthy individuals. METHODS: Healthy subjects and individuals with stroke were recruited. Both groups were assessed using the WBB-based posturography system. Individuals with stroke were also assessed using a laboratory grade posturography system and a battery of clinical tests to determine the concurrent validity of the system. A group of subjects were assessed twice with the WBB-based system to determine its reliability. RESULTS: A total of 144 healthy individuals and 53 individuals with stroke participated in the study. Concurrent validity with another posturography system was moderate to high. Correlations with clinical scales were consistent with previous research. The reliability of the system was excellent in almost all measures. In addition, the system successfully characterized individuals with stroke with respect to the healthy population. CONCLUSIONS: The WBB-based posturography system exhibited excellent psychometric properties and sensitivity for identifying balance performance of individuals with stroke in comparison with healthy subjects, which supports feasibility of the system as a clinical tool.

Emergence of virtual reality as a tool for upper limb rehabilitation: incorporation of motor control and motor learning principles.

The primary focus of rehabilitation for individuals with loss of upper limb movement as a result of acquired brain injury is the relearning of specific motor skills and daily tasks. This relearning is essential because the loss of upper limb movement often results in a reduced quality of life. Although rehabilitation strives to take advantage of neuroplastic processes during recovery, results of traditional approaches to upper limb rehabilitation have not entirely met this goal. In contrast, enriched training tasks, simulated with a wide range of low- to high-end virtual reality-based simulations, can be used to provide meaningful, repetitive practice together with salient feedback, thereby maximizing neuroplastic processes via motor learning and motor recovery. Such enriched virtual environments have the potential to optimize motor learning by manipulating practice conditions that explicitly engage motivational, cognitive, motor control, and sensory feedback-based learning mechanisms. The objectives of this article are to review motor control and motor learning principles, to discuss how they can be exploited by virtual reality training environments, and to provide evidence concerning current applications for upper limb motor recovery. The limitations of the current technologies with respect to their effectiveness and transfer of learning to daily life tasks also are discussed.

Visual conflict and cognitive load modify postural responses to vibrotactile noise.

BACKGROUND: Underlying the increased incidence of falls during multitasking is a reduced ability to detect or attend to the sensory information signaling postural instability. Adding noise to a biological system has been shown to enhance the detection and transmission of weakened or sub-threshold cutaneous signals. If stochastic resonance is to become an effective adjunct to rehabilitation, we need to determine whether vibrotactile noise can be effective when added to an environment presenting with other sensory noise. METHODS: Sub-threshold vibration noise was applied for 30 sec at the soles of the feet in 21 healthy adults (20-29 yrs) between two 30-sec periods of no vibration. During the trials, subjects stood quietly with eyes closed or while viewing a visual scene that rotated in continuous upward pitch at 30 deg/sec. Subjects were also tested with these two visual conditions while performing a mental calculation task. It was hypothesized that sub-threshold vibration would increase regularity of postural sway, thereby improving postural stabilization during an attention demanding task but exerting less effect with multiple sensory demands. An ellipse fit to the covariance matrix revealed excursion of center of pressure (COP) and center of mass (COM) responses in the anterior-posterior and lateral planes. RMS values and approximate entropy of the COP and COM were calculated and statistically compared. RESULTS: The addition of vibrotactile noise to the plantar surface during quiet stance with eyes closed reduced the area of the COM and COP responses, which then returned to pre-vibration levels after vibration was removed. Postural sway was generally increased with both visual field rotations and mental calculation compared to the eyes closed condition. The effect of sub-threshold vibratory noise on postural behavior was modified when visual field rotations and mental calculation was combined. It was shown that the measure of approximate entropy reflected increased task complexity. CONCLUSIONS: Our results suggest that the impact of destabilizing signals is modulated when combined with vibrotactile stimulation. The strong aftereffects of the vibration stimulus suggest that the system has adapted to the sensory array even in the short time period tested here. The results imply that application of vibrotactile stimulation has the potential for diminishing sway magnitudes while increasing the potential for response variability, thereby presenting a non-invasive method of reducing the potential for falls.

Postural responses of adults with cerebral palsy to combined base of support and visual field rotation.

We employed a virtual environment to examine the postural behaviors of adults with cerebral palsy (CP). Four adults with CP (22-32 years) and nine healthy adults (21-27 years) were tested with a Rod and Frame protocol. They then stood quietly on a platform within a three-wall virtual environment. The platform was either kept stationary or tilted 3(°) into dorsiflexion in the dark or with pitch up and down visual field rotations at 30(°)/s and 45(°)/s. While the visual field rotated, the platform was held tilted for 30 s and then slowly returned to a neutral position over 30 s. Center of pressure (CoP) was recorded and center of mass (CoM) as well as trunk and ankle angles were calculated. Electromyography (EMG) responses of the ankle and the hip muscles were recorded and analyzed using wavelets. Larger angular deviations from vertical and horizontal in the Rod and Frame test indicated that adults with CP were more visually dependent than healthy adults. Adults with CP had difficulty maintaining balance when standing on a stationary platform during pitch upward rotation of the visual scene. When the platform was tilted during visual field rotations, adults with CP took longer to stabilize their posture and had larger CoM oscillations than when in the dark. The inability to compensate for busy visual environments could impede maintenance of functional locomotion in adults with CP. Employing a visual field stimulus for assessment and training of postural behaviors would be more meaningful than testing in the dark.

Head stabilization shows visual and inertial dependence during passive stimulation: implications for virtual rehabilitation.

Sensorimotor coordination relies on the fine calibration and integration of visual, vestibular, and somatosensory input. Using virtual environments (VE) allows for the dissociation of visual and inertial inputs to manipulate human behavioral outputs. Our goal was to employ VE technology in a novel manner to investigate how head stabilization is affected by spatiotemporal properties of dynamic visual input when combined with passive motion on a linear sled. Healthy adults (n = 12) wore a head-mounted display during naso-occipital sinusoidal horizontal whole body translations while seated. Subjects were secured in a seat with a five-point harness, with the head free to move. Frequency and amplitude of sinusoidal input (i.e., inertial conditions) were set to create overlapping conditions of maximum acceleration (amax) or velocity (vmax). Four inertial conditions were combined with four visual conditions (VIS). VIS were created so that direction of optic flow either matched direction of passive motion or did not. The effect of near and far fixation distance within the VE was also tested. Head kinematics were collected with a three-axis gyro. Head stability showed a complex interaction dependent on changes in weighting of visual and inertial inputs that changed with the sled driving frequency. Inertial condition affected amplitude (p < 0.0000) and phase (p < 0.0000) of head pitch angular velocity. In the absence of visual input, head pitch velocity amplitude increased (p < 0.01). An interaction effect between inertial and VIS conditions on head yaw occurred in SW (p < 0.05). There was also a significant interaction of depth of field and inertial condition on amplitude (p < 0.001) and phase (p < 0.05) of head yaw velocity in SW, especially during high vmax conditions. We conclude visual flow can organize lateral cervical responses despite being discordant with inertial input. When using VE for rehabilitation, possible unintended, involuntary or reflexive motor responses that may not be present in traditional training environments should be taken into consideration.

Fear of falling and balance ability in older men: the priest study.

Studies examining fear of falling among older adult men remain limited. The objectives of this study were to compare balance confidence in 2 age cohorts of older clergy and identify predictive determinants of balance confidence in a liturgical research initiative. Participants included 131 community-dwelling Roman Catholic priests age 60-97 yr living in religious communities in 10 mid-Atlantic states. Subjects completed the Activities-specific Balance Confidence Scale (ABC), Berg Balance Scale (BBS), timed up-and-go (TUG) test, and 15-item Geriatric Depression Scale (GDS). Younger priests (60-74 yr) demonstrated a significantly higher ABC score than the older cohort (75 and above yr) of priests (89.1 ± 12.6 vs.78.4 ± 13.9, p = .001). Confidence was significantly correlated with BBS (rho = .69, p < .01), TUG (r = -.58, p < .01), and GDS (r = -.39, p < .01) scores. A stepwise-regression model demonstrated that balance ability, mood, assistive-device use, and physical activity predicted 52% of the variance in balance confidence.

Reorientation to vertical modulated by combined support surface tilt and virtual visual flow in healthy elders and adults with stroke.

We explored how changes in visual attention impacted postural motor performance in healthy elders and adults post-stroke within a virtual reality environment, including when vestibular information was not perceptible. Visual dependence in 13 healthy (50-80 years) and 13 adults post-stroke (49-70 years) was assessed with a rod-and-frame task. Three degree support surface dorsiflexion tilts at 30°/s were combined with 30° and 45°/s continuous pitch rotations of the visual environment. The support surface remained tilted for 30 s followed by a 0.1°/s return to neutral during continued visual field rotation. Body displacement and ankle muscle responses were recorded, and wavelet transforms calculated. Muscle frequencies and kinematic measures were examined with functional principal component analysis, and weights compared through mixed model repeated measures ANOVA. Both populations exhibited increased backward sway with pitch upward visual field motion; adults post-stroke produced significantly larger muscle responses. Lateral sway was most regulated when visual flow velocity matched platform velocity. Visual flow summed with direction of support surface instability and visually dependent individuals produced more controlled lateral sway when viewing a dynamic visual field. Provoking postural instability within a dynamic visual flow field could serve as a training tool for postural stabilizing actions, particularly when visual dependence is exhibited.

Continuous visual field motion impacts the postural responses of older and younger women during and after support surface tilt.

The effect of continuous visual flow on the ability to regain and maintain postural orientation was examined. Fourteen young (20-39 years old) and 14 older women (60-79 years old) stood quietly during 3° (30°/s) dorsiflexion tilt of the support surface combined with 30° and 45°/s upward or downward pitch rotations of the visual field. The support surface was held tilted for 30 s and then returned to neutral over a 30-s period while the visual field continued to rotate. Segmental displacement and bilateral tibialis anterior and gastrocnemius muscle EMG responses were recorded. Continuous wavelet transforms were calculated for each muscle EMG response. An instantaneous mean frequency curve (IMNF) of muscle activity, center of mass (COM), center of pressure (COP), and angular excursion at the hip and ankle were used in a functional principal component analysis (fPCA). Functional component weights were calculated and compared with mixed model repeated measures ANOVAs. The fPCA revealed greatest mathematical differences in COM and COP responses between groups or conditions during the period that the platform transitioned from the sustained tilt to a return to neutral position. Muscle EMG responses differed most in the period following support surface tilt indicating that muscle activity increased to support stabilization against the visual flow. Older women exhibited significantly larger COM and COP responses in the direction of visual field motion and less muscle modulation when the platform returned to neutral than younger women. Results on a Rod and Frame test indicated that older women were significantly more visually dependent than the younger women. We concluded that a stiffer body combined with heightened visual sensitivity in older women critically interferes with their ability to counteract posturally destabilizing environments.