The Reliance on Vestibular Information During Standing Balance Control Decreases With Severity of Vestibular Dysfunction

Comparative analysis of sensory-motor function and its correlation with gait biomechanics in patients with unilateral chronic ankle instability

OBJECTIVE

This study was to evaluate the correlation between postural stability, proprioception, tactile sensation, and gait biomechanics in young patients with unilateral chronic ankle instability (CAI).

METHODS

A total of 85 patients with CAI (80% females) and 51 healthy individuals (78% females) aged 18-35 years were recruited for this study. Standardized tests were used to assess bilateral sensory-motor function and gait biomechanics, to compare differences in sensory-motor function and gait biomechanics between groups, and to analyze the correlation between sensory-motor function and gait on the affected side of CAI patients. Postural stability was quantified by jump-landing test for stabilization time in the anterior-posterior direction; proprioception was quantified by bilateral thresholds for ankle plantarflexion, dorsiflexion, inversion, and eversion; and plantar sensation was determined by measuring the minimum thresholds of sensation in the five plantar regions. Gait biomechanics were analyzed by collecting ankle dorsiflexion-plantarflexion/inversion-exversion range of motion and ankle-toe kinetic parameters during barefoot walking.

RESULTS

Compared with Non-CAI, CAI patients had longer stabilization time in both anterior-posterior directions bilaterally (P = 0.015, P = 0.024); longer stabilization time was observed only in the medial-lateral direction on the affected side (P = 0.012). Thresholds for plantarflexion, dorsiflexion, inversion, and eversion of the ankle joint were higher bilaterally in CAI than in Non-CAI (all P < 0.05); tactile sensation was reduced bilaterally in CAI for the big toe, the 1st metatarsal head, the 5th metatarsal head, the lateral arch, and the heel (all P < 0.05); and gait biomechanics were reduced bilaterally in CAI patients than in Non-CAI individuals (all P < 0.05). Thresholds for plantarflexion, dorsiflexion, inversion, and eversion had significant negative correlations with gait biomechanics (r > 0.5, P < 0.05). There was a weak to moderate correlation between the lowest tactile sensation thresholds at the big toe and heel and gait biomechanics (r > 0.3, P < 0.05). No significant correlation was observed between stabilization time and gait biomechanics (P < 0.05).

CONCLUSION

Young patients with unilateral CAI have poor bilateral postural stability, proprioception and tactile deficits, and altered gait biomechanics. These changes not only affect the affected side but also involve the non-affected side.

Head position control strategies in progressive Supranuclear Palsy versus Idiopathic Parkinson's Disease during dynamic-on-static platform tilt

Objectives

We investigated differences in head stabilization among Progressive Supranuclear Palsy (PSP), advanced Idiopathic Parkinson's Disease (IPD) and healthy controls during passive anteroposterior platform tilting to determine factors for disease-specific falling.

Methods

Seventeen PSP, eleven IPD and eighteen control subjects were exposed to pseudorandom multi-frequency antero-posterior platform tilts, while recording 3D motion of body segments with a Zebris ultrasound positioning system. Fourier transforms were computed from the time series datasets to assess transfer functions between stimuli (platform tilts) and responses (angles of the head, trunk and hip in space).

Results

Overall head excursions in space among PSP was several times increased in relation to IPD and controls. The stimulus driven contribution to the head movement, i.e., the GAIN of the transfer function between platform stimulus and head movement, was double the amount of the values derived from IPD and 5-fold relative to controls. GAIN of the transfer function was the highest among the middle tilt frequencies 0.15-0.4 Hz, and was independent from the eyes open vs. closed condition.

Conclusion

PSP patients' head excursions with respect to the shoulder girdle and trunk were exceptionally increased, compared to IPD and controls. The source for the larger excursions, however, was not related to an unspecific lack of head stabilization, but was instead determined by a central strategy. Consistent with pathoanatomical degeneration of mesencephalic supracollicular pathways processing visual flow or vestibular pathways, PSP resorted to egocentric proprioceptive-dominated stabilization to the surface, rather than allocentric stabilization in space like IPD. Passive neck rigidity in PSP did not contribute significantly.

Significance

The axial muscle rigidity emphasized in PSP versus IPD did not contribute to body instability in the sensory context of unstable surfaces. Instead, deficits in processing of visual and vestibular information played a larger role in PSP falling than previously known.

Development and validation of a two-dimensional pseudorandom balance perturbation test

Introduction

Pseudorandom balance perturbations use unpredictable disturbances of the support surface to quantify reactive postural control. The ability to quantify postural responses to a continuous multidirectional perturbation in two orthogonal dimensions of sway (e.g., AP and ML) has yet to be investigated.

Methods

We developed a balance perturbation paradigm that used two spectrally independent sum of sinusoids signals (SoS1, SoS2), one for each orthogonal dimension of tilt (roll and pitch), to deliver a two-dimensional (2D) balance perturbation. In a group of 10 healthy adults we measured postural sway during 2D perturbations, as well as for each of the two individual 1D perturbation components.

Results

We found that during 2D perturbations, spectral peaks in the sway response were larger at the perturbed frequencies when compared to (1) the adjacent non-perturbed frequencies and (2) the frequencies contained within the orthogonal, spectrally independent perturbation signal. We also found that for each of the two spectra (SoS1, SoS2), the magnitude and timing of the sway response relative to the platform disturbance was similar when measured during 1D and 2D conditions.

Discussion

These data support that our novel 2D SoS perturbation test was able to evoke ML and AP postural responses that were (1) specific to the roll and pitch perturbations, respectively, and (2) similar to the responses provoked by individual 1D perturbations.

Postural impairments in unilateral and bilateral vestibulopathy

Chronic imbalance is a major complaint of patients suffering from bilateral vestibulopathy (BV) and is often reported by patients with chronic unilateral vestibulopathy (UV), leading to increased risk of falling. We used the Central SensoriMotor Integration (CSMI) test, which evaluates sensory integration, time delay, and motor activation contributions to standing balance control, to determine whether CSMI measures could distinguish between healthy control (HC), UV, and BV subjects and to characterize vestibular, proprioceptive, and visual contributions expressed as sensory weights. We also hypothesized that sensory weight values would be associated with the results of vestibular assessments (vestibulo ocular reflex tests and Dizziness Handicap Inventory scores). Twenty HCs, 15 UVs and 17 BVs performed three CSMI conditions evoking sway in response to pseudorandom (1) surface tilts with eyes open or, (2) surface tilts with eyes closed, and (3) visual surround tilts. Proprioceptive weights were identified in surface tilt conditions and visual weights were identified in the visual tilt condition. BVs relied significantly more on proprioception. There was no overlap in proprioceptive weights between BV and HC subjects and minimal overlap between UV and BV subjects in the eyes-closed surface-tilt condition. Additionally, visual sensory weights were greater in BVs and were similarly able to distinguish BV from HC and UV subjects. We found no significant correlations between sensory weights and the results of vestibular assessments. Sensory weights from CSMI testing could provide a useful measure for diagnosing and for objectively evaluating the effectiveness of rehabilitation efforts and future treatments designed to restore vestibular function such as hair cell regeneration and vestibular implants.

Increased roll tilt thresholds are associated with subclinical postural instability in asymptomatic adults aged 21 to 84 years

Background

Balance assessments that intentionally alter the reliability of visual and proprioceptive feedback (e.g., standing on foam with eyes closed) have become a standard approach for identifying vestibular mediated balance dysfunction in older adults. However, such assessments cannot discern which specific element of the vestibular system (e.g., semicircular canal, otolith, or combined canal-otolith) underlies the observed age-related changes in balance performance. The present study was designed to determine the associations between specific sources of vestibular noise and quantitative measures of quiet stance postural control measured during standard "vestibular" balance conditions.

Methods

A group of 52 asymptomatic adults (53.21 ± 19.7, 21 to 84 years) without a history of vestibular or neurologic disorders volunteered for this study. We measured a battery of five vestibular perceptual thresholds that assay vestibular noise with predominant contributions from the vertical canals, lateral canals, utricles, saccules, and the centrally integrated canal-otolith signal. In addition, participants completed two standard balance assessments that were each designed to prioritize the use of vestibular cues for quiet stance postural control-eyes closed on foam (Condition 4 of the Modified Romberg Balance Test) and eyes closed, on a sway referenced support surface (Condition 5 of the Sensory Organization Test).

Results

In age adjusted models, we found strong positive associations between roll tilt vestibular thresholds, a measure of noise in the centrally integrated canal-otolith signal, and the root mean square distance (RMSD) of the anteroposterior and mediolateral center of pressure (CoP) captured during eyes closed stance on a sway referenced support surface. The strength of the association between roll tilt thresholds and the RMSD of the CoP was between 3-times and 30-times larger than the association between postural sway and each of the other vestibular thresholds measured.

Conclusion

We posit that noise in the centrally estimated canal-otolith "tilt" signal may be the primary driver of the subclinical postural instability experienced by older adults during the "vestibular" conditions of balance assessments. Additional testing in adults with clinical balance impairment are needed to identify if roll tilt thresholds may also serve as a surrogate metric by which to detect vestibular mediated balance dysfunction and/or fall risk.

Central sensorimotor integration assessment reveals deficits in standing balance control in people with chronic mild traumatic brain injury

Imbalance is common following mild Traumatic Brain Injury (mTBI) and can persist months after the initial injury. To determine if mTBI subjects with chronic imbalance differed from healthy age- and sex-matched controls (HCs) we used both the Central SensoriMotor Integration (CSMI) test, which evaluates sensory integration, time delay, and motor activation properties and the standard Sensory Organization Test (SOT). Four CSMI conditions evoked center-of-mass sway in response to: surface tilts with eyes closed (SS/EC), surface tilts with eyes open viewing a fixed visual surround (SS/EO), visual surround tilts with eyes open standing on a fixed surface (VS/EO), and combined surface and visual tilts with eyes open (SS+VS/EO). The mTBI participants relied significantly more on visual cues during the VS/EO condition compared to HCs but had similar reliance on combinations of vestibular, visual, and proprioceptive cues for balance during SS/EC, SS/EO, and SS+VS/EO conditions. The mTBI participants had significantly longer time delays across all conditions and significantly decreased motor activation relative to HCs across conditions that included surface-tilt stimuli with a sizeable subgroup having a prominent increase in time delay coupled with reduced motor activation while demonstrating no vestibular sensory weighting deficits. Decreased motor activation compensates for increased time delay to maintain stability of the balance system but has the adverse consequence that sensitivity to both internal (e.g., sensory noise) and external disturbances is increased. Consistent with this increased sensitivity, SOT results for mTBI subjects showed increased sway across all SOT conditions relative to HCs with about 45% of mTBI subjects classified as having an “Aphysiologic” pattern based on published criteria. Thus, CSMI results provided a plausible physiological explanation for the aphysiologic SOT pattern. Overall results suggest that rehabilitation that focuses solely on sensory systems may be incomplete and may benefit from therapy aimed at enhancing rapid and vigorous responses to balance perturbations.

Contributions of Body-Orientation to Mental Ball Dropping Task During Out-of-Body Experiences

Out-of-body experiences (OBEs) provide fascinating insights into our understanding of bodily self-consciousness and the workings of the brain. Studies that examined individuals with brain lesions reported that OBEs are generally characterized by participants experiencing themselves outside their physical body (i.e., disembodied feeling) (Blanke and Arzy, 2005). Based on such a characterization, it has been shown that it is possible to create virtual OBEs in immersive virtual environments (Ehrsson, 2007; Ionta et al., 2011b; Bourdin et al., 2017). However, the extent to which body-orientation influences virtual OBEs is not well-understood. Thus, in the present study, 30 participants (within group design) experienced a full-body ownership illusion (synchronous visuo-tactile stimulation only) induced with a gender-matched full-body virtual avatar seen from the first-person perspective (1PP). At the beginning of the experiment, participants performed a mental ball dropping (MBD) task, seen from the location of their virtual avatar, to provide a baseline measurement. After this, a full-body ownership illusion (embodiment phase) was induced in all participants. This was followed by the virtual OBE illusion phase of the experiment (disembodiment phase) in which the first-person viewpoint was switched to a third-person perspective (3PP), and participants' disembodied viewpoint was gradually raised to 14 m above the virtual avatar, from which altitude they repeated the MBD task. During the experiment, this procedure was conducted twice, and the participants were allocated first to the supine or the standing body position at random. Results of the MBD task showed that the participants experienced increased MBD durations during the supine condition compared to the standing condition. Furthermore, although the findings from the subjective reports confirmed the previous findings of virtual OBEs, no significant difference between the two postures was found for body ownership. Taken together, the findings of the current study make further contributions to our understanding of both the vestibular system and time perception during OBEs.

Type of exercise may influence postural adaptations in chemotherapy-induced peripheral neuropathy

OBJECTIVE

Traditional posturography measurements characterize postural instability in patients with chemotherapy-induced peripheral neuropathy (CIPN), while underlying postural control mechanisms remain unclear. Taking a model-based approach can yield insights into these mechanisms. This study's aim was to characterize the modifications in postural control of CIPN patients associated with exercise in relation to the postural behavior of healthy control participants (hCON) via an exploratory approach.

METHODS

Thirty-one CIPN patients were randomly assigned to two interventions (balance plus moderate endurance training vs. moderate endurance training only) and exercised twice per week over 12 weeks. Baseline data were compared to 36 matched hCONs. We recorded spontaneous sway and postural reactions to platform tilts using Optotrak and a Kistler force platform pre- and post-intervention. Data interpretation relied on a model-based parameter identification procedure.

RESULTS

Spontaneous sway amplitudes were larger and postural reactions smaller, with a relative phase advance, in our pre-intervention patients than the hCONs. Post-intervention, spontaneous sway, and postural reactions were reduced and the sensory-motor ratio larger in both groups, while the postural reaction timing differed between groups.

INTERPRETATION

The abnormally small postural reactions in CIPN patients before the intervention can be interpreted as the consequence of abnormally strong velocity control-a strategy modification that may serve as a prediction mechanism to compensate for the lack of timely and accurate proprioceptive signals. While both groups reduced postural sway and showed an adapted sensory-motor ratio post-intervention, the interventions seemed to trigger different velocity control strategies. This study emphasizes the need for taking a more differentiated perspective on intervention effects.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS) number: DRKS00005419, prospectively registered on November 19, 2013.

Comparison of Activity-Based Home Program and Cawthorne-Cooksey Exercises in Patients With Chronic Unilateral Peripheral Vestibular Disorders

OBJECTIVE

This study aimed to investigate the effects of an activity-based home program and an exercise-based home program on dizziness severity, balance, and independent level of daily life activities in patients with dizziness due to chronic unilateral peripheral vestibular disorders.

DESIGN

A single-blind randomized controlled trial.

SETTING

University dizziness management clinics.

PARTICIPANTS

Individuals (N=75) between 18 and 65 years of age who had chronic unilateral peripheric vestibular disorders and vestibular rehabilitation indication.

INTERVENTION

Participants were randomly divided into 3 groups: an activity-based home program (group 1/activity group), an exercise-based home program (group 2/exercise group), and a control group (group 3). After an initial assessment, all groups participated in the patient education program. In addition, the activity-based home program was administered to the first group, while the Cawthorne-Cooksey home exercise program was administered to the second group.

MAIN OUTCOME MEASURES

Visual analog scale (VAS), Vestibular Disorders Activities of Daily Living Scale (VADL), and computerized dynamic posturography before and immediately after the treatment program.

RESULTS

A statistically significant improvement was found in the activity and exercise groups in terms of VAS, VADL, Sensory Organization Test (SOT) 5, SOT 6, and SOT (composite) scores compared with the control group (P<.05). A statistically significant improvement was found in the activity group in terms of the instrumental subscale of VADL, SOT 5, SOT 6, and SOT (composite) scores compared with the exercise group.

CONCLUSIONS

The activity-based home program was more effective in improving the home management task, the occupational task, and balance than the exercise-based home treatment program in patients with chronic peripheral vestibular disorders.

Preliminary study on an added vestibular-ocular reflex visual conflict task for postural control

BACKGROUND

Using the modified-Clinical Test of Sensory Integration and Balance (m-CTSIB), clinicians can assess sensory feedback systems of the visual, vestibular, and somatosensory systems on postural control. However, with growing vestibulo-ocular reflex (VOR) assessment, the addition of a VOR task, for sensory feedback on postural control has yet to be investigated.

AIM

The aim of the study was to examine the preliminary effect of an added VOR visual conflict task during postural control conditions of the m-CTSIB at baseline and re-test reliability.

METHODS

Seventeen healthy college-aged individuals completed a baseline m-CTSIB with an added VOR visual conflict condition consisting of a lateral headshake and follow-up assessment occurring 72-h after baseline. Measures consisted of m-CTSIB sway scores on individual conditions of eyes open and eyes closed tasks on firm and foam surfaces. A series of Wilcoxon matched-pairs signed-rank tests were conducted to determine the differences between the VOR condition and the m-CTSIB conditions. A Spearman Rank Order correlation was used to examine the retest reliability.

RESULTS

The VOR visual conflict task condition produced worse sway index scores than eyes-open firm and foam (p<0.001), but better scores than eyes-closed foam (P=0.01) conditions at baseline. VOR tasks on their respective firm (r_s=0.81) and foam surface (r_s=0.83) were strongly correlated at 72-h retest.

CONCLUSIONS

The addition of a VOR visual conflict task condition differed from the other conditions of the m-CTSIB, further targeting the vestibular-ocular system from the vestibular-spinal system during postural control. Incorporating a VOR task during postural stability may create greater postural control deficits in individuals with vestibular-ocular dysfunction. Test-retest correlations at 72-h were clinically acceptable.

RELEVANCE FOR PATIENTS

Addition of a VOR task as visual conflict condition of the m-CTSIB may assist in additional sensory system feedback for concussion assessment.

Altered postural timing and abnormally low use of proprioception in lumbar spinal stenosis pre- and post- surgical decompression

Background

Lumbar spinal stenosis (LSS) is frequently associated with postural instability. Although several studies evaluated patients’ functional impairments, underlying sensorimotor mechanisms are still poorly understood. We aimed to assess the specific set of postural control deficits associated with LSS during spontaneous and externally perturbed stance and evaluated post-surgical changes in postural behavior.

Methods

We analyzed postural control in eleven LSS patients (age 69 ± 8 years) pre- and post-laminectomy, correlated experimental data with functional tests and patient-reported outcomes, and compared findings to 15 matched, healthy control subjects (age 70 ± 6 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by anterior-posterior pseudorandom tilts of the body support surface. We used an established postural control model to extract specific postural control parameters.

Results

Spontaneous sway amplitude, velocity and frequency were abnormally large in LSS patients. Furthermore, patients’ postural reactions to platform tilts, represented by GAIN and PHASE were significantly altered. Based on simple feedback model simulations, we found that patients rely less on proprioceptive cues for stance regulation than healthy subjects. Moreover, their postural reactions’ timing is altered. After surgery, patients’ spontaneous sway amplitude was significantly reduced and their postural timing approximated the behavior of healthy subjects.

Conclusion

The reduction in proprioceptive input for stance control due to stenosis-caused afferent dysfunction is a functional disadvantage for LSS patients – and may be the basis of increased spontaneous sway. This disadvantage may cause the timing of postural reactions to alter, with the intent of preventing rapid changes in stance regulation for safety reasons. After surgery, patients’ postural timing approximated those of healthy subjects, while the abnormally low use of proprioception remained unchanged. We suggest the post-surgery rehabilitation of proprioception, eg through balance exercises on unstable surfaces and reduced visual input.

Implementation of a Central Sensorimotor Integration Test for Characterization of Human Balance Control During Stance

Balance during stance is regulated by active control mechanisms that continuously estimate body motion, via a "sensory integration" mechanism, and generate corrective actions, via a "sensory-to-motor transformation" mechanism. The balance control system can be modeled as a closed-loop feedback control system for which appropriate system identification methods are available to separately quantify the sensory integration and sensory-to-motor components of the system. A detailed, functionally meaningful characterization of balance control mechanisms has potential to improve clinical assessment and to provide useful tools for answering clinical research questions. However, many researchers and clinicians do not have the background to develop systems and methods appropriate for performing identification of balance control mechanisms. The purpose of this report is to provide detailed information on how to perform what we refer to as "central sensorimotor integration" (CSMI) tests on a commercially available balance test device (SMART EquiTest CRS, Natus Medical Inc, Seattle WA) and then to appropriately analyze and interpret results obtained from these tests. We describe methods to (1) generate pseudorandom stimuli that apply cyclically-repeated rotations of the stance surface and/or visual surround (2) measure and calibrate center-of-mass (CoM) body sway, (3) calculate frequency response functions (FRFs) that quantify the dynamic characteristics of stimulus-evoked CoM sway, (4) estimate balance control parameters that quantify sensory integration by measuring the relative contribution of different sensory systems to balance control (i.e., sensory weights), and (5) estimate balance control parameters that quantify sensory-to-motor transformation properties (i.e., feedback time delay and neural controller stiffness and damping parameters). Additionally, we present CSMI test results from 40 subjects (age range 21-59 years) with normal sensory function, 2 subjects with results illustrating deviations from normal balance function, and we summarize results from previous studies in subjects with vestibular deficits. A bootstrap analysis was used to characterize confidence limits on parameters from CSMI tests and to determine how test duration affected the confidence with which parameters can be measured. Finally, example results are presented that illustrate how various sensory and central balance deficits are revealed by CSMI testing.