Postural imbalance with head extension: improvement by training as a model for ataxia therapy

Postural stability in strabismus and amblyopia

BACKGROUND

Postural control is a complex skill based on the collaboration of dynamic sensory mechanisms, namely the visual, vestibular, and somatosensory systems.

METHODS

A literature survey regarding postural stability in strabismus and amblyopia was conducted using databases in order to collect data for a narrative review of published reports and available literature.

RESULTS

The results of the literature survey were analyzed to provide an overview of the current knowledge of postural stability in strabismus and amblyopia. The results revealed that although postural control depends on the fundamental integration of three essential components (the visual, vestibular, and somatosensory systems), the role of vision is critical in postural stability. Once normal binocular vision is undesirably disrupted in childhood by some reason, especially in strabismus and/or amblyopia, balance is also affected. Abnormal balance affects coordination in gross and fine motor controls in school-age children and results in weakened academic performance and delayed social progress. It also impacts a child's general health, self-esteem, and safety.

CONCLUSIONS

Binocular vision is imperative for the maturation and preservation of balance control in children, as balance performance is reduced in strabismus and/or amblyopia.

Comparison of proprioceptive postural control strategies between prolonged standing induced low back pain developers and non-low back pain developers

BACKGROUND

Proprioception deficit has been suggested as a possible mechanism contributing for the impaired postural control in low back pain (LBP) patients. Whether proprioception deficit is a result of or a cause of LBP has not been investigated.

OBJECTIVE

The purpose of this study was to compare proprioceptive postural control strategies between prolonged standing induced low back pain developers (PDs) and non-pain developers (NPDs).

METHOD

Thirty-two healthy subjects performed 1-h prolonged standing and their ratings of perceived LBP have been recorded. Eight quiet standing trials for 60 s performed immediately before and after the prolonged standing. Postural control was challenged by muscle vibration and different postural conditions during quiet standing. Data were recorded using a force platform.

RESULTS

Forty percentage of participants is classified as PD. Before the prolonged standing, relative proprioceptive weighting was greater in the PD compared to NPD group (P = .029). Main effect of postural condition (F_1,24 = 5.21, P = .032) and interaction of time by group (F_1,24 = 8.08, P = .009) were significant for COP displacement in anteroposterior direction. Interaction of postural condition by group (F_1,26 = 7.82, P = .010) and time by group (F_1,26 = 9.71, P = .004) were significant for COP displacement in mediolateral direction. Main effect of postural condition (F_1,26 = 6.31, P = .018) and interaction of postural condition by group (F_1,26 = 7.07, P = .013) were significant for mean velocity in mediolateral direction.

CONCLUSION

The PD group has altered proprioceptive postural control strategies before and after prolonged standing. Proprioception deficit should not be considered to be solely an adaptive response and may be causal for LBP development.

Head and neck extension more than 30° may disturb standing balance in healthy older adults

Although there is clinical evidence of postural instability at extreme angles of head extension, the effects of lower angles on balance have been not investigated. This study aimed to investigate the effects of different head and neck extension angles on standing balance in older adults, and to determine the critical angle of instability. Twenty-eight healthy older adults were tested at 0°, 20°, 30° and 40° head and neck extension. The center of pressure (COP) parameters were recorded with a force plate. Significant differences were observed between 30° and 40° compared to 0° in anteroposterior and mediolateral COP displacement and total COP velocity, and between 40° and 0° in mediolateral COP velocity. Head and neck extension at 30° was the critical angle associated with the appearance of instability, and this value should be considered in the ergonomic design of work and living spaces, exercise programming and daily activities in older adults.

Free Energy Principle in Human Postural Control System: Skin Stretch Feedback Reduces the Entropy

Human upright standing involves an integration of multiple sensory inputs such as vision, vestibular and somatosensory systems. It has been known that sensory deficits worsen the standing balance. However, how the modulation of sensory information contributes to postural stabilization still remains an open question for researchers. The purpose of this work was to formulate the human standing postural control system in the framework of the free-energy principle, and to investigate the efficacy of the skin stretch feedback in enhancing the human standing balance. Previously, we have shown that sensory augmentation by skin stretch feedback at the fingertip could modulate the standing balance of the people with simulated sensory deficits. In this study, subjects underwent ten 30-second trials of quiet standing balance with and without skin stretch feedback. Visual and vestibular sensory deficits were simulated by having each subject close their eyes and tilt their head back. We found that sensory augmentation by velocity-based skin stretch feedback at the fingertip reduced the entropy of the standing postural sway of the people with simulated sensory deficits. This result aligns with the framework of the free energy principle which states that a self-organizing biological system at its equilibrium state tries to minimize its free energy either by updating the internal state or by correcting body movement with appropriate actions. The velocity-based skin stretch feedback at the fingertip may increase the signal-to-noise ratio of the sensory signals, which in turn enhances the accuracy of the internal states in the central nervous system. With more accurate internal states, the human postural control system can further adjust the standing posture to minimize the entropy, and thus the free energy.

Towards computerized diagnosis of neurological stance disorders: data mining and machine learning of posturography and sway

We perform classification, ranking and mapping of body sway parameters from static posturography data of patients using recent machine-learning and data-mining techniques. Body sway is measured in 293 individuals with the clinical diagnoses of acute unilateral vestibulopathy (AVS, n = 49), distal sensory polyneuropathy (PNP, n = 12), anterior lobe cerebellar atrophy (CA, n = 48), downbeat nystagmus syndrome (DN, n = 16), primary orthostatic tremor (OT, n = 25), Parkinson's disease (PD, n = 27), phobic postural vertigo (PPV n = 59) and healthy controls (HC, n = 57). We classify disorders and rank sway features using supervised machine learning. We compute a continuous, human-interpretable 2D map of stance disorders using t-stochastic neighborhood embedding (t-SNE). Classification of eight diagnoses yielded 82.7% accuracy [95% CI (80.9%, 84.5%)]. Five (CA, PPV, AVS, HC, OT) were classified with a mean sensitivity and specificity of 88.4% and 97.1%, while three (PD, PNP, and DN) achieved a mean sensitivity of 53.7%. The most discriminative stance condition was ranked as "standing on foam-rubber, eyes closed". Mapping of sway path features into 2D space revealed clear clusters among CA, PPV, AVS, HC and OT subjects. We confirm previous claims that machine learning can aid in classification of clinical sway patterns measured with static posturography. Given a standardized, long-term acquisition of quantitative patient databases, modern machine learning and data analysis techniques help in visualizing, understanding and utilizing high-dimensional sensor data from clinical routine.

Differences in postural stability and dynamic visual acuity among healthy young adults in relation to sports activity: a cross sectional study

[Purpose] Sports activity has been shown to improve postural stability and vestibular function in healthy older adults. The hypothesis was that healthy young adults undertaking sports activity will also have better postural stability and vestibular function compared with healthy young adults who do not undertake sports activity. The purpose of this study was to investigate the differences in postural stability and vestibular function between healthy young adults who undertake sports activity and those who do not undertake such activity. [Participants and Methods] Thirty-nine healthy young adults were recruited and divided into sports and non-sports groups on the basis of their response to a questionnaire concerning regular participation in sports activities over the past 12 months. In both groups, postural stability was measured during quiet standing and standing during head rotation, and dynamic visual acuity was assessed during head rotation. [Results] The results showed significant differences in postural stability during head rotation and dynamic visual acuity between the two groups, whereas no significant differences were found in postural stability during quiet standing. [Conclusion] The results suggest that healthy young adults who undertake sports activity have better postural stability during head rotation and better dynamic visual acuity. The causal effect of these differences is not clear and further investigation is warranted.

Effects of Vestibular Rehabilitation on Dizziness and Imbalance

Vestibular rehabilitation is a specific approach to physical therapy aimed at reducing dizziness and imbalance by facilitating central nervous system compensation for peripheral vestibular dysfunction. This article reports preliminary results of studies concerning the relative effectiveness of vestibular rehabilitation, general conditioning exercises, and vestibular suppressant medication on dizziness and imbalance in patients with chronic vestibular symptoms of at least 6 months duration. Patients with positional and/or movement-related dizziness and abnormal posturography were randomly assigned to the three treatment groups. Preliminary results suggest that although all three treatment approaches reduce dizziness, only vestibular rehabilitation also improves balance. This study takes the first step toward determining the efficacy of a specific exercise approach for reducing dizziness and imbalance in patients with chronic peripheral vestibular disorders.

Postural control and balance in a cohort of healthy people living in Europe: An observational study

In the past 20 years, posturography has been widely used in the medical field. This observational study aimed to report the values derived from posturography of a wide set of healthy subjects from various European countries using a plantar pressure platform and a standardized method of measurement.A random cluster sampling of 914 healthy subjects aged between 7.0 and 85.99 years, stratified by age, was carried out. To provide percentile values of our cohort, data were processed to obtain 3 curves corresponding to the following percentiles: 25th, 50th, 75th, and the interquartile range. Distance-weighted least squares method was used to represent the percentile on appropriate graphs.In our sample, the balance to improve with age, up to approximately 45 years, but the trend to reverse with older age. The data show that the oscillations on the sagittal plane (y-mean) change with advancing age. Young people had more retro-podalic support than older people; the balance shifted forward in elderly people.As the study included a relatively large quantity of data collected using a standardized protocol, these results could be used as normative values of posturography for similar populations. On the basis of this data, correct diagnostic clues will be available to clinicians and professionals in the field. However, further studies are needed to confirm our findings.

Neurovestibular Symptoms in Astronauts Immediately after Space Shuttle and International Space Station Missions

OBJECTIVES

(1) To assess vestibular changes and related sensorimotor difficulties, especially instability of posture and gait, among astronauts immediately after they return from space and to compare the effects experienced after short- and long-duration space missions. (2) To determine whether any difficulties experienced were severe enough to impair the astronauts' ability to leave the spacecraft in the event of an emergency.

STUDY DESIGN

Prospective cohort study.

SETTING

National Aeronautics and Space Administration's Kennedy Space Center and Johnson Space Center.

SUBJECTS AND METHODS

Fourteen crewmembers of 3 Space Shuttle missions that lasted about 1 week and 18 crewmembers of 8 International Space Station missions that lasted about 6 months were given brief vestibular examinations 1 to 5 hours after landing. These examinations focused on the presence of vestibular and motor coordination difficulties, as well as motion sickness and motion sensations. Standardized tests included the observation of abnormal eye movements, finger-to-nose pointing, standing up from a seated position, postural stability, and tandem gait.

RESULTS

Unsteady walking and postural instabilities were observed after short- and long-duration missions. Motion sickness symptoms were observed after long-duration missions but not after short-duration missions. The symptom most frequently reported by the astronauts was an exaggerated perceived motion associated with sudden head movements during reentry and after landing.

CONCLUSION

The severity of the observed abnormalities would limit the ability of crewmembers during the first 5 hours after landing and increase the time required to leave the spacecraft during this period.

Treatment of the Mal de Debarquement Syndrome: A 1-Year Follow-up

The mal de debarquement syndrome (MdDS) is a movement disorder, occurring predominantly in women, is most often induced by passive transport on water or in the air (classic MdDS), or can occur spontaneously. MdDS likely originates in the vestibular system and is unfamiliar to many physicians. The first successful treatment was devised by Dai et al. (1), and over 330 MdDS patients have now been treated. Here, we report the outcomes of 141 patients (122 females and 19 males) treated 1 year or more ago. We examine the patient’s rocking frequency, body drifting, and nystagmus. The patients are then treated according to these findings for 4–5 days. During treatment, patients’ heads were rolled while watching a rotating full-field visual surround (1). Their symptom severity after the initial treatment and at the follow-up was assessed using a subjective 10-point scale. Objective measures, taken before and at the end of the week of treatment, included static posturography. Significant improvement was a reduction in symptom severity by more than 50%. Objective measures were not possible during the follow-up because of the wide geographic distribution of the patients. The treatment group consisted of 120 classic and 21 spontaneous MdDS patients. The initial rate of significant improvement after a week of treatment was 78% in classic and 48% in spontaneous patients. One year later, significant improvement was maintained in 52% of classic and 48% of spontaneous subjects. There was complete remission of symptoms in 27% (32) of classic and 19% (4) of spontaneous patients. Although about half of them did not achieve a 50% improvement, most reported fewer and milder symptoms than before. The success of the treatment was generally inversely correlated with the duration of the MdDS symptoms and with the patients’ ages. Prolonged travel by air or car on the way home most likely contributed to the symptomatic reversion from the initial successful treatment. Our results indicate that early diagnosis and treatment can significantly improve results, and the prevention of symptomatic reversion will increase the long-term benefit in this disabling disorder.

Change in the natural head-neck orientation momentarily altered sensorimotor control during sensory transition

Achilles tendon vibration generates proprioceptive information that is incongruent with the actual body position; it alters the perception of body orientation leading to a vibration-induced postural response. When a person is standing freely, vibration of the Achilles tendon shifts the internal representation of the verticality backward thus the vibration-induced postural response realigned the whole body orientation with the shifted subjective vertical. Because utricular otoliths information participates in the creation of the internal representation of the verticality, changing the natural orientation of the head-neck system during Achilles tendon vibration could alter the internal representation of the earth vertical to a greater extent. Consequently, it was hypothesized that compared to neutral head-neck orientation, alteration in the head-neck orientation should impair balance control immediately after Achilles tendon vibration onset or offset (i.e., sensory transition) as accurate perception of the earth vertical is required. Results revealed that balance control impairment was observed only immediately following Achilles tendon vibration offset; both groups with the head-neck either extended or flexed showed larger body sway (i.e., larger root mean square scalar distance between the center of pressure and center of gravity) compared to the group with the neutral head-neck orientation. The fact that balance control was uninfluenced by head-neck orientation immediately following vibration onset suggests the error signal needs to accumulate to a certain threshold before the internal representation of the earth vertical becomes incorrect.

Postural balance control in women with generalized joint laxity

Objectives

This study aims to investigate the potential relationship between joint laxity and postural balance by using tetra-ataxiometric posturography (Tetrax®).

Patients and methods

A total of 69 healthy volunteers were included in the study and classified into three groups based on their hypermobility severity determined with Beighton-Horan hypermobility index scores. Of those, 29 participants were non-hypermobile, 13 participants were mildly hypermobile and remaining 27 patients had severe hypermobility. Postural control of the participants was evaluated by using the Tetrax® device in eight different positions. The stability index, Fourier index, weight distribution index, and synchronization index scores of each participant were recorded.

Results

We found that the participants with severe hypermobility exhibited significantly higher stability index scores while the position of the head is extended and rotated right. The weight distribution index on elastic surfaces was impaired in non-hypermobile and severely hypermobile participants. We observed that the Fourier Index scores were higher at a higher-medium frequency (0.5-1 Hz) in participants with severe hypermobility. There was no difference between the groups in terms of synchronization index scores.

Conclusion

These findings suggest that severely hypermobile individuals have a decreased postural stability in head-extended and head- rotated positions when compared to individuals who are non-hypermobile. This increased instability may lead to an increased risk of musculoskeletal injuries, especially in sports that require extension and rotation movements of the head.

Modified head shake sensory organization test: Sensitivity and specificity

The Sensory Organization Test (SOT) of Computerized Dynamic Posturography (EquiTest™ equipment) is a valuable tool for investigating how an individual uses balance system sensory input (vestibular, vision, proprioception/somatosensory) to maintain quiet stance; however, it is limited as a screening tool for identifying peripheral vestibular system dysfunction. Previous research has shown that adding horizontal head-shake to portions of the standard SOT battery improved the identification of peripheral vestibular system asymmetry; however, flaws in the methods were noted. The objective of this work was to evaluate the sensitivity and specificity of the modified head-shake SOT (HS-SOT) protocol for identification of peripheral vestibular system lesion. Fifteen patients with chief complaint of instability, vertigo, and/or lightheadedness, with and without a caloric unilateral weakness (UW) and fifteen age-matched healthy controls were included in the final analysis. Ten of the 15 patients demonstrated a caloric UW≥25%. Participants completed standard conditions 2 and 5 of SOT with head still and during four horizontal head-shaking tasks (i.e., HS-SOT2-60°/s, HS-SOT2-120°/s, HS-SOT5-15°/s, and HS-SOT5-60°/s). Average equilibrium scores decreased as condition difficulty increased (SOT2, HS-SOT2-60°/s, HS-SOT2-120°/s, SOT 5, HS-SOT5-15°/s, and HS-SOT5-60°/s) for each group; as expected, a lower decline was noted for controls (slope=-6.59) compared to patients (slope=-11.69). The HS-SOT5-15°/s condition was superior for identifying peripheral vestibular asymmetry (AUC=0.90 sensitivity=70%, specificity=100%), with the strongest correlation to caloric UW% (rs=-0.743, p=0.000006). HS-SOT5-15°/s appears to be a promising screening measure for peripheral vestibular asymmetry.

PROSPERA: a randomized, controlled trial evaluating rasagiline in progressive supranuclear palsy

To date, pharmacological treatment options for progressive supranuclear palsy (PSP), a neurodegenerative tauopathy, are limited. The MAO-B inhibitor rasagiline has shown neuroprotective effects in preclinical models of neurodegeneration. To evaluate the safety, tolerability and therapeutic effect of rasagiline on symptom progression in PSP. In this 1-year randomized, double-blind, placebo-controlled trial, 44 patients fulfilling the NINDS-PSP criteria were randomized to 1 mg/d rasagiline or placebo. The combined primary endpoint included symptom progression as measured by the PSP rating scale (PSP-RS) and the requirement of L-dopa rescue medication. Secondary endpoints included Schwab and England Activities of Daily Living (SEADL), Montgomery-Åsberg Depression Rating Scale, Mini Mental State Examination, Frontal Assessment Battery and posturographic measurements. Of the 44 patients randomized, 26 completed the trial per protocol. Rasagiline was well tolerated, with a slight increase of known side effects (hallucinations, ventricular extrasystoles). No effect on the primary endpoint (p = 0.496) was detected. Symptom progression averaged at 11.2 (rasagiline) and 10.8 (placebo) points per year (ΔPSP-RS). No difference was seen in SEADL, depression, cognitive function, frontal executive function and posturographic measurements. Post hoc analyses of PSP-RS subdomains indicate a potential beneficial effect in the "limb motor" subdomain, whereas performance appeared lower in the "mentation" and "history" subdomains in the treatment group. While rasagiline is well tolerated in PSP, a beneficial effect on overall symptom progression was not detected. Post hoc analyses suggest the implementation of more specific endpoints in future studies.

A Portable Sensory Augmentation Device for Balance Rehabilitation Using Fingertip Skin Stretch Feedback

Neurological disorders are the leading causes of poor balance. Previous studies have shown that biofeedback can compensate for weak or missing sensory information in people with sensory deficits. These biofeedback inputs can be easily recognized and converted into proper information by the central nervous system (CNS), which integrates the appropriate sensorimotor information and stabilizes the human posture. In this study, we proposed a form of cutaneous feedback which stretches the fingertip pad with a rotational contactor, so-called skin stretch. Skin stretch at a fingertip pad can be simply perceived and its small contact area makes it favored for small wearable devices. Taking advantage of skin stretch feedback, we developed a portable sensory augmentation device (SAD) for rehabilitation of balance. SAD was designed to provide postural sway information through additional skin stretch feedback. To demonstrate the feasibility of the SAD, quiet standing on a force plate was evaluated while sensory deficits were simulated. Fifteen healthy young adults were asked to stand quietly under six sensory conditions: three levels of sensory deficits (normal, visual deficit, and visual + vestibular deficits) combined with and without augmented sensation provided by SAD. The results showed that augmented sensation via skin stretch feedback helped subjects correct their posture and balance, especially as the deficit level of sensory feedback increased. These findings demonstrate the potential use of skin stretch feedback in balance rehabilitation.

Selective activation of ipsilateral motor pathways in intact humans

It has been proposed that ipsilateral motor pathways play a role in the control of ipsilateral movements and recovery of function after injury. However, the extent to which ipsilateral motor pathways are engaged in voluntary activity in intact humans remains largely unknown. Using transcranial magnetic stimulation over the arm representation of the primary motor cortex, we examined ipsilateral motor-evoked potentials (iMEPs) in a proximal arm muscle during increasing levels of unilateral and bilateral isometric force in a sitting position. We demonstrate that iMEP area and amplitude decreased during bilateral contraction of homonymous (elbow flexor) muscles and increased during bilateral contraction of heteronymous (elbow flexor and extensor) muscles compared with a unilateral contraction, regardless of the level of force tested. To further understand the neuronal inputs involved in the bilateral effects, we examined the contribution from neck afferents projecting onto ipsilateral motor pathways. Medial (away from the muscle tested) and lateral (toward the muscle tested) rotation of the head enhanced bilateral iMEP effects from homonymous and heteronymous muscles, respectively. In contrast, head flexion and extension exerted nonspecific bilateral effects on iMEPs. Intracortical inhibition, in the motor cortex where iMEPs originated, showed modulation compatible with the changes in iMEPs. We conclude that ipsilateral projections to proximal arm muscles can be selectively modulated by voluntary contraction of contralateral arm muscles, likely involving circuits mediating asymmetric tonic neck reflexes acting, at least in part, at the cortical level. The pattern of bilateral actions may represent a strategy to engage ipsilateral motor pathways in a motor behavior.

Readaptation of the vestibulo-ocular reflex relieves the mal de debarquement syndrome

The mal de debarquement syndrome (MdDS), a continuous feeling of swaying, rocking, and/or bobbing, generally follows travel on the sea. The associated symptoms cause considerable distress. The underlying neural mechanisms are unknown, and to date there have been no effective treatments for this condition. Results in monkeys and humans suggested that MdDS was caused by maladaptation of the vestibulo-ocular reflex (VOR) to roll of the head during rotation. We studied 24 subjects with persistent MdDS (3 males, 21 females; 19.1 ± 33 months). Physical findings included body oscillation at 0.2 Hz, oscillating vertical nystagmus when the head was rolled from side-to-side in darkness, and unilateral rotation during the Fukuda stepping test. We posited that the maladapted rocking and the physical symptoms could be diminished or extinguished by readapting the VOR. Subjects were treated by rolling the head from side-to-side while watching a rotating full-field visual stimulus. Seventeen of the 24 subjects had a complete or substantial recovery on average for approximately 1 year. Six were initially better, but the symptoms recurred. One subject did not respond to treatment. Thus, readaptation of the VOR has led to a cure or substantial improvement in 70% of the subjects with MdDS. We conclude that the adaptive processes associated with roll-while-rotating are responsible for producing MdDS, and that the symptoms can be reduced or resolved by readapting the VOR.

Subjective visual vertical and postural performance in healthy children

Introduction

Verticality is essential in our life, especially for postural stability. Subjective vertical as well as postural stability depends on different sensorial information: visual, vestibular and somesthesic. They help to build the spatial referentials and create a central representation of verticality. Children are more visuo-dependant than adults; however, we did not find any study focusing on how children develop their sense of verticality.

Methods

We studied two groups of subjects: 10 children (from 6 to 8 years) and 12 young adults. We recorded postural stability with a Techno Concept plateform and perception of subjective visual vertical in the following conditions: while adjusting the vertical in the dark or with visual perturbation, while fixating the vertical bar, and with eyes closed.

Results

Children are more instable than adults in terms of postural parameters, and also while performing a double task, especially when no visual references are present. They also present a higher variability and lower accuracy than adults in reporting their perception of true vertical reference.

Discussion

Children might have limited attentional resources, and focus their attention on the more demanding task, corresponding to the U-shaped non-linear model.

Static and dynamic body balance following provocation of the visual and vestibular systems in females with and without joint hypermobility syndrome

OBJECTIVES

Joint hypermobility syndrome (JHS) is a heritable disorder of the connective tissue characterized by excessive joint movement, musculoskeletal pain and neurophysiological deficits (i.e. decreased proprioceptive acuity, altered neuromuscular reflexes). Such deficits may affect body balance thus increasing the risk of injury. The present study aimed at examining static and dynamic body balance following challenge of the visual and vestibular systems in individuals with JHS.

METHODS

The sample consisted of 21 females with JHS and 20 controls without signs of JHS. Static body balance was assessed by the degree of anteroposterior and mediolateral deviation of the center of pressure, during 20-sec single-leg stances with eyes opened (EO), eyes closed (EC) and eyes opened with head extension (EO-HE) using a foot pressure platform. Dynamic body balance was assessed by the number of landing and balance errors committed during a multiple single-leg-hop-stabilization test.

RESULTS

Nonparametric analysis showed that the JHS-group demonstrated significantly greater (a) mediolateral deviation during single-leg-stance with EO (p < 0.01), (b) mediolateral and anteroposterior deviation during single-leg-stance with EO-HE (p < 0.05), and (c) number of landing errors (p < 0.05) compared to the control group.

CONCLUSIONS

Poor static balance following challenge of the vestibular system may be justified by vestibular deficiency and/or insufficient proprioceptive capabilities of the neck. Impairments of dynamic balance in individuals with JHS may be attributed to proprioceptive deficits, which can alter feedforward and feedback mechanisms.

Sensory Re-Weighting in Human Bipedal Postural Control: The Effects of Experimentally-Induced Plantar Pain

The present study was designed to assess the effects of experimentally-induced plantar pain on the displacement of centre of foot pressure during unperturbed upright stance in different sensory conditions of availability and/or reliability of visual input and somatosensory input from the vestibular system and neck. To achieve this goal, fourteen young healthy adults were asked to stand as still as possible in three sensory conditions: (1) No-vision, (2) Vision, and (3) No-vision - Head tilted backward, during two experimental conditions: (1) a No-pain condition, and (2) a condition when a painful stimulation was applied to the plantar surfaces of both feet (Plantar-pain condition). Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed that (1) experimentally-induced plantar pain increased CoP displacements in the absence of vision (No-vision condition), (2) this deleterious effect was more accentuated when somatosensory information from the vestibular and neck was altered (No-vision - Head tilted backward condition) and (3) this deleterious effect was suppressed when visual information was available (Vision condition). From a fundamental point of view, these results lend support to the sensory re-weighting hypothesis whereby the central nervous system dynamically and selectively adjusts the relative contributions of sensory inputs (i.e. the sensory weightings) in order to maintain balance when one or more sensory channels are altered by the task (novel or challenging), environmental or individual conditions. From a clinical point of view, the present findings further suggest that prevention and treatment of plantar pain may be relevant for the preservation or improvement of balance control, particularly in situations (or individuals) in which information provided by the visual, neck proprioceptive and vestibular systems is unavailable or disrupted.

Efficacy of a vibrotactile neurofeedback training in stance and gait conditions for the treatment of balance deficits: a double-blind, placebo-controlled multicenter study

OBJECTIVE

Vestibular rehabilitation strategies mostly require a long-lasting training in stance conditions, which is finally not always successful. The individualized training in everyday-life conditions with an intuitive tactile neurofeedback stimulus seems to be a more promising approach. Hence, the present study was aimed at investigating the efficacy of a new vibrotactile neurofeedback system for vestibular rehabilitation.

STUDY DESIGN

Double-blinded trial.

PATIENTS

One hundred five patients who experience one of the following balance disorders for more than 12 months were included in the study: canal paresis, otolith disorder, removal of an acoustic neuroma, microvascular compression syndrome, Parkinson's disease, and presbyvertigo.

INTERVENTIONS

Vibrotactile neurofeedback training was performed daily (15 min) over 2 weeks with the Vertiguard system in those 6 tasks of the Standard Balance Deficit Test with the most prominent deviations from the normative values.

MAIN OUTCOME MEASURES

Trunk and ankle sway, dizziness handicap inventory, and vestibular symptom score were measured in the verum and placebo group before the training, on the last training day and 3 months later.

RESULTS

A significant reduction in trunk and ankle sway as well as in the subjective symptom scores were observed in the verum group. Such an effect could not be found in any of the outcome parameters of the placebo group.

CONCLUSION

The vibrotactile neurofeedback training applied in the present study is a highly efficient method for the reduction of body sway in different balance disorders. Because the rehabilitation program is easy to perform, not exhausting, and time saving, elderly patients and those with serious, long-lasting balance problems also can participate successfully.

Gender differences in postural stability among children

This study aimed to examine the gender differences in postural stability among 8–12 year-old children. Twenty-six children participated in this repeated measures study to measure the centre of pressure (COP) under one normal condition (CONTROL: hard surface, eyes open, and looking straight ahead) and two challenging sensory conditions (ECHB: eyes closed and head back; and EOCS: eyes open and compliant surface) in randomized order. Girls had significantly lower COP path velocity (COP-PV, p < 0.05, medium effect), smaller radial displacement (COP-RD, p < 0.05, medium effect), and lower area velocity (COP-AV, p < 0.05, medium effect) as compared to boys when the three conditions were pooled. Gender differences were found in the percentage changes in COP-RD during ECHB (p < 0.05, large effect) and EOCS (p < 0.05, medium effect), and in COP-AV during both ECHB and EOCS conditions (p < 0.05, medium effect). Postural stability performance of girls had higher correlations with age (−0.62 vs. −0.40), body mass (−0.60 vs. −0.42), foot length (−0.68 vs. −0.45), and physical activity level (−0.45 vs. 0.02), as compared to boys. Girls had better postural stability than boys but were more affected by altered sensory input information. Girls are more capable of integrating their sensory inputs, whereas boys treat each sensory input somewhat separately and rely more on somatosensory feedback. Exercises such as standing on unstable surfaces with eyes open instead of eye closed and head back are more beneficial to children’s postural stability control system.

Improving balance skills in patients who had stroke through virtual reality treadmill training

OBJECTIVE

The aim of this study was to evaluate the effects of virtual reality (VR) treadmill training on the balance skills of patients who have had a stroke.

DESIGN

A total of 14 patients with strokes were recruited and randomly assigned to receive VR treadmill or traditional treadmill training. The outcome measures that were included for the study were center of pressure (COP) sway excursion, COP maximum sway in anterior-posterior direction, COP maximum sway in medial-lateral direction, COP sway area, bilateral limb-loading symmetric index, the sway excursion values for the paretic foot (sway excursion/P), paretic limb stance time (stance time/P), number of steps of the paretic limb (number of steps/P), and contact area of the paretic foot (contact A/P) during quiet stance, sit-to-stand transfer, and level walking.

RESULTS

There were no significant improvements in COP-related measures and symmetric index during the quiet stance, either in the VR treadmill or traditional treadmill training group (P > 0.05). However, the difference between groups after training in COP maximum sway in medial-lateral direction during the quiet stance was significant (P = 0.038). Traditional treadmill training failed to improve sit-to-stand performance, whereas VR treadmill training improved symmetric index (P = 0.028) and sway excursion (P = 0.046) significantly during sit-to-stand transfer. The changes of symmetric index between groups were markedly different (P = 0.045). Finally, both groups improved significantly in stance time/P, but only VR treadmill training increased contact A/P (P = 0.034) after training during level walking. The difference between groups during level walking was not significant.

CONCLUSIONS

Neither traditional treadmill nor VR treadmill training had any effect on balance skill during quiet stance, but VR treadmill training improved balance skill in the medial-lateral direction better than traditional training did. VR treadmill training also improved balance skill during sit-to-stand transfers and the involvement of paretic limb in level walking more than the traditional one did.

Effect of chewing gum on static posturography in patients with balance disorders

CONCLUSION

The chewing gum indirectly affects postural control by influencing vestibular function to stabilize posture during upright standing.

OBJECTIVES

This study aimed to evaluate the effect of chewing gum on static posturography in patients.

METHODS

The subjects were 26 patients with chronic balance disorders. The subjects were instructed to stand as stably as possible on the force platform. The recording was conducted four times. For the first evaluation, postural sway was measured during motionless standing. Two weeks after the recording, the postural sway was recorded again as a second evaluation. Thereafter, the subjects were instructed to chew gum for 3 min. The third evaluation was conducted while the subjects continued to chew gum. Then 1 h after the subject had stopped chewing gum, a fourth evaluation was obtained. The total path length (LNG) and rectangle area (REC) were analyzed.

RESULTS

We found that postural stability tended to improve while the subjects masticated gum. Both LNG and REC were significantly improved while the subjects chewed gum with their eyes closed. In patients without canal paralysis (CP), the measurements of LNG with eyes closed and REC with eyes open were significantly decreased while masticating gum. In patients with CP, the REC, but not LNG, was significantly decreased while masticating gum both with eyes open and eyes closed.

Assessment of diagnostic accuracy of foam posturography for peripheral vestibular disorders: analysis of parameters related to visual and somatosensory dependence

OBJECTIVES

Simple tests to detect peripheral vestibulopathy might be practically useful before conducting elaborate examinations. The purpose of this study was to assess the diagnostic accuracy of foam posturography for peripheral vestibulopathy, with emphasis on visual and somatosensory dependence.

METHODS

Two-legged stance tasks were conducted in patients with unilateral (n=68) and bilateral (n=16) vestibulopathy and healthy controls (n=66), under four conditions; eyes open with and without the foam rubber, and eyes closed with and without the foam rubber.

RESULTS

The values of six parameters; the velocity of movement of the center of pressure (COP) and envelopment area tracing by the movement of the COP in eyes closed/foam rubber, the Romberg's ratios of velocity and area with foam rubber, and the foam ratios (ratios of a measured parameter with to without the foam rubber), of velocity and area in eyes closed, were significantly higher in unilateral and bilateral vestibulopathy compared with the control (p<0.001). The area under the receiver operating characteristic curve for the Romberg's ratio of velocity with the foam rubber was the largest.

CONCLUSIONS

Foam posturography detected high levels of visual and somatosensory dependence in patients with vestibulopathy.

SIGNIFICANCE

Foam posturography is useful for preliminary assessment of possible peripheral vestibulopathy.

Correlations between posturographic findings and symptoms in subjects with fractures of the condylar head of the mandible

Our study examined the posture of 15 patients who had sustained a simple unilateral or bilateral fracture of the condylar head of the mandible as a result of sports or traffic accidents. Following preliminary testing of vestibular function, the patients underwent balance testing: Romberg test with eyes closed (EC), Romberg EC and bite test (ECBT), EC and head retroflexed (ECR). The study parameters were: surface (S) of the statokinesigram, stomatognathic influence index related to S (SSI), and postural oscillations on the frontal plane (X). In keeping with the literature, we felt that the following pattern in static balance suggested a posture destabilised by the stomatognathic system: SSI values of less than 60, reduction of S in the transition from EC to ECR, pathological increase of postural oscillations on the X plane. The study was completed by obtaining a list of new symptoms reported by the patients (altered bite, fullness, tinnitus, pain, loss of balance). The most significant patterns were observed in patients with vestibular dysfunctions and neck pain. It seems that a fracture of the condylar head can affect postural behaviour, although proprioceptive changes alone are not enough to cause true loss of balance and there must be concomitant vestibular dysfunction. The stabilometric pattern is not conditioned by the extent of the trauma or the related treatment. In terms of proprioceptive elements, the presence of muscle pain seems to point to cervical muscle tension as the main culprit in the onset of posttraumatic instability.

Vestibular rehabilitation by auditory feedback in otolith disorders

Rehabilitation strategies have been applied successfully over the last few decades to initiate central compensation of the tonus imbalance and to facilitate substitution in different types of peripheral vestibular dysfunction. However, these vestibular rehabilitation strategies are often not successful in patients with isolated otolith disorders. The aim of the present study was therefore to evaluate a specific rehabilitation strategy for patients with an isolated otolith disorder by using an auditory feedback system. Thirteen patients, which suffered from different types of otolith disorders, but no other vestibular pathology and 13 normal controls were included in this study. Vestibular rehabilitation exercises were performed daily over a 2-week period (weekends excluded). During all exercises the patients of the test group (n=13) obtained an acoustic feedback signal when their trunk angle velocity exceeded a preset level while the patients of the control group (n=13) performed the same exercises without auditory feedback. The most effective exercise in the test group was "walking eight tandem steps on a foam support surface". Approximately 85% of the patients showed a significant decrease of trunk sway in this condition. In contrast to these results, patients of the control group showed no significant improvement of postural control after the training. The results indicate that an auditory feedback rehabilitation program with exercises related to the specific neurotological disease could significantly improve the postural control in patients with otolith disorders.

Artificial neural network: a new diagnostic posturographic tool for disorders of stance

OBJECTIVE

To determine the accuracy of diagnoses made with artificial neural network techniques (ANNW) that identify postural sway patterns typical for balance disorders.

METHODS

Body sway was measured by means of posturography during 10 test conditions of increasing difficulty. From a database of 676 subjects 60 training cases (TCs) and 60 validation cases (VCs) were selected in which the following diagnoses had been established clinically: normal subject (NS), postural phobic vertigo (PPV), anterior lobe cerebellar atrophy (CA), primary orthostatic tremor (OT), and acute unilateral vestibular neuritis (VN). A standard 3-layer feed-forward ANNW, using the backpropagation algorithm, was trained with TCs, validated with VCs, and its accuracy tested on 5 new cases.

RESULTS

ANNW differentiated the established diagnoses with an overall sensitivity and specificity of 0.93. Sensitivity and specificity were 1 for NS and OT; for PPV, 0.87 and 0.96; for CA, 1 and 0.98; and for VN, 0.8 and 0.98, respectively. New subjects were identified with ANNW output variables of the true diagnoses between 0.73 and 1.

CONCLUSIONS

ANNW differentiates postural sway patterns of several distinct clinical balance disorders with high sensitivity and specificity. Once designed and tested ANNW could be considered a black box, which each examiner can apply to predict a specific diagnosis even without a clinical examination.

SIGNIFICANCE

A promising diagnostic tool for disorders of upright stance in selected neurological disorders.

Destabilization of human balance control by static and dynamic head tilts

To better understand the effects of varying head movement frequencies on human balance control, 12 healthy adult humans were studied during static and dynamic (0.14, 0.33, 0.6 Hz) head tilts of +/- 30 degrees in the pitch and roll planes. Postural sway was measured during upright stance with eyes closed and altered somatosensory inputs provided by a computerized dynamic posturography (CDP) system. Subjects were able to maintain upright stance with static head tilts, although postural sway was increased during neck extension. Postural stability was decreased during dynamic head tilts, and the degree of destabilization varied directly with increasing frequency of head tilt. In the absence of vision and accurate foot support surface inputs, postural stability may be compromised during dynamic head tilts due to a decreased ability of the vestibular system to discern the orientation of gravity. This instability may compound the risk of falling following recovery from balance disorders or adaptation to altered gravity conditions such as space flight. Thus, dynamic head tilts may improve the diagnostic sensitivity of computerized dynamic posturography, particularly for healthy subjects recovering from temporary balance control deficits.

Head and body sway in response to vertical visual stimulation

CONCLUSIONS

Postural responses differed according to the stimulus direction, i.e. vertical visual stimulation induced head rather than trunk displacements. Accordingly, it could be that center of foot pressure (COP) responses tended to underestimate the postural sway during visual stimulation.

OBJECTIVES

To investigate head and body sway in response to vertical visual surround motion, and to examine the correlation between the displacements of head and body segments derived from video-motion analysis and COP measurements.

MATERIAL AND METHODS

Postural sway was assessed in 10 young female subjects by video-motion analysis of four different head and body segments, and by use of force-plate posturography. Head and body sway in the pitch plane was induced by rotating a random pattern of dots about the subject's inter-aural axis at a constant acceleration of 1 degree/s(2) or a constant velocity of 60 degrees/s in darkness.

RESULTS

Generally, head displacement was greater than that of other body parts during vertical optokinetic stimulation (OKS). In most subjects, maximum head displacements were induced in the same direction as the visual motion. Downward OKS induced a forward head and body sway. The COP trajectory correlated well with the displacements of each head and body segment during downward OKS. In contrast, postural responses to upward OKS were complicated in terms of their time course. The correlation coefficient between each head and body segment and the COP varied among individuals for upward OKS.

Effects of head extension on undisturbed upright stance control in humans

The purpose of the present experiment was to investigate whether and how the head extended posture, commonly encountered in many routine activities, affects undisturbed upright stance control mechanisms in humans. Sixteen young healthy adults stood feet together, with their eyes closed and were asked to sway as little as possible in two Neutral and Extended head conditions. Centre of pressure (CP) displacements, recorded using a force platform, were used to compute the motions of the vertical projection of the centre of gravity (CG(v)) and those of the difference CP - CG(v). A time-domain analysis shows increased mean velocity and surface covered by the trajectory of both elementary motions in the Extended head condition. A frequency analysis also reveals increased root mean squares on the CP - CG(v) motions, suggesting increased muscular activity in the Extended head condition. Furthermore, similar changes occur on CG(v) motions. Finally, modelling these trajectories as a fractional Brownian motion process demonstrates increased spatial transition point co-ordinates at which the corrective process is initiated and a more deterministic control mechanism in this corrective process involving CG(v) motions in the Extended head position. Together, the present findings suggest that head extension position yields a reorganisation of the control mechanisms for maintaining undisturbed upright stance.

Does head extension and flexion increase postural instability in elderly subjects when visual information is kept constant?

The present study determined the effects of flexing and extending the head on the postural stability and mean anterior-posterior (A-P) center of mass (CM) position during upright stance in the elderly. To ensure visual input to stability was not a confounding variable, visual information was kept as constant as possible for all head positions. Twelve healthy elderly subjects (72.3 +/- 4.7 years) were asked to stand stationary on a single force-platform. Postural stability (assessed using the rms A-P excursion of the center of pressure (CP)) was determined for standing with the head erect, and with the head flexed and extended. The vestibular contribution to postural stability becomes increasingly important under challenging conditions, so to highlight the effects of vestibular system input, measurements of postural stability under conditions where visual and somatosensory inputs were disrupted were included. Changes in the mean A-P CM position when tilting the head were assessed by determining changes in the mean A-P location of the CP from standing with the head erect. Compared to standing with the head erect and looking straight ahead, postural stability was reduced when the head was flexed or extended (P < 0.01). Changes in mean A-P CM position were only significant when standing with the head flexed (P < 0.05). This suggests that increases in postural instability with the head tilted from the erect position may be in part due to mechanical perturbation rather than solely vestibular disruption.

Neck muscle fatigue and spatial orientation during stepping in place in humans

Neck proprioceptive input, as elicited by muscle vibration, can produce destabilizing effects on stance and locomotion. Neck muscle fatigue produces destabilizing effects on stance, too. Our aim was to assess whether neck muscle fatigue can also perturb the orientation in space during a walking task. Direction and amplitude of the path covered during stepping in place were measured in 10 blindfolded subjects, who performed five 30-s stepping trials before and after a 5-min period of isometric dorsal neck muscle contraction against a load. Neck muscle electromyogram amplitude and median frequency during the head extensor effort were used to compute a fatigue index. Head and body kinematics were recorded by an optoelectronic system, and stepping cadence was measured by sensorized insoles. Before the contraction period, subjects normally stepped on the spot or drifted forward. After contraction, some subjects reproduced the same behavior, whereas others reduced their forward progression or even stepped backward. The former subjects showed minimal signs of fatigue and the latter ones marked signs of fatigue, as quantified by the dorsal neck electromyogram index. Head position and cadence were unaffected in either group of subjects. We argue that the abnormal fatigue-induced afferent input originating in the receptors transducing the neck muscle metabolic state can modulate the egocentric spatial reference frame. Notably, the effects of neck muscle fatigue on orientation are opposite to those produced by neck proprioception. The neck represents a complex source of inputs capable of modifying our orientation in space during a locomotor task.

Exercise and drug therapy alter recovery from labyrinth lesion in humans

Acute unilateral vestibular failure is characterized by rotatory vertigo, horizontal-rotatory nystagmus, and postural imbalance, all of which last from days to weeks. These signs and symptoms are caused by a vestibular tone imbalance between the two labyrinths. Recovery results from a combination of peripheral restoration of labyrinthine function (usually incomplete) and central vestibular compensation (CVC) of the vestibular tone imbalance. Acute unilateral failure is most often caused by vestibular neuritis, which is most likely due to the reactivation of a latent HSV-1 infection. Therefore, therapeutic strategies to improve the outcome of VN are theoretically based on two principles: (a) vestibular exercises and drugs to improve CVC and (b) drug treatment of the assumed viral inflammation. The following conclusions can be drawn from studies in animals and/or humans: (1) There is strong evidence that vestibular exercises may improve vestibulo-spinal compensation. These exercises should begin as early as possible after symptom onset. Moreover, slower exercises are likely to be more effective than faster exercises because slower ones seem to depend more on the vestibular system. (2) Despite extensive data from animal experiments indicating that drugs have a favorable effect on CVC, this has not been clinically proven and thus cannot be recommended yet. (3) Preliminary results of an interim analysis from an ongoing randomized, prospective study showed that methylprednisolone (plus an antiviral agent?) may be useful for improving peripheral vestibular function in vestibular neuritis.

[Results of videonystagmographic (VNG) analysis in vestibular post-traumatic pathology]

From February 1998 to July 1999, 569 patients affected by vestibular disorders--following a whiplash injury and/or a cranial trauma--were studied. The neuro-otological examination included a tonal audiometry, brain stem auditory evoked potentials, clinical and instrumental vestibular tests (caloric test, rotatory test, assessment of visually guided eye movements). The study of eye movements was conducted with the support of the Ulmer video-oculographical system. The aim of the research was to analyse, both from a qualitative and a quantitative perspective, the vestibular and clinical findings. Particular emphasis was laid on the incidence of the "up-beating" nystagmus in different categories of patients, all supported by a statistical study. As a result, an etiopathogenetical hypothesis of the nystagmus was advanced, based on altered otolithic and cervical inputs. At the same time, the importance of the video-nystagmographical system was stressed, to the extent that it leads to a standardised and objective analysis, fundamental for clinical and forensic aspects.

Dynamic balance function in phasic cervical dystonia following Botulinum toxin therapy

Previous research by our group revealed normal dynamic balance function in pure tonic cervical dystonia (CD) with impaired equilibrium in phasic CD patients investigated at least 3 months following Botulinum toxin (BtxA) treatment. The current study was performed to determine whether impaired dynamic equilibrium in phasic CD is influenced by symptomatic treatment with BtxA. Dynamic balance was tested in 20 patients with phasic CD on a dynamic platform with a cylindrical curved base (stabilometer) 4 weeks following BtxA treatment. Balance was assessed by the linear displacement of the platform and the maximum amplitude of platform displacement with open and closed eyes and compared with pre-BtxA data. Despite a clinically significant BtxA-induced reduction of phasic head movements, none of the platform measures improved significantly. In addition, there was no correlation between the BtxA-induced clinical improvement and changes in any of the dynamic balance measures pre- vs. post-BtxA. In conclusion, the persistent dynamic balance impairment after effective BtxA therapy may indicate that disequilibrium in phasic CD does not simply reflect disturbed vestibular input from repetitive head oscillations, but argues in favour of different sensorimotor processing in tonic and phasic CD.

Patients with somatoform phobic postural vertigo: the more difficult the balance task, the better the balance performance

The objective was to test, whether the increased body sway activity, shown in patients with phobic postural vertigo (PPV) in a previous posturographic study, impairs postural balance during demanding balance tasks. In 17 patients with PPV and 15 normal subjects body sway was analyzed for two standing positions on a foam rubber-padded posturographic platform with the eyes open or closed: (a) normal upright stance, (b) tandem stance. During normal upright stance patients showed an increase in body sway activity between 0.1 and 19 Hz and in sway path values for lateral and fore/aft directions. During the most difficult balance task, i.e. tandem stance with the eyes closed, body sway activity and sway path values did not differ between patients and controls. Objective balance skills were not impaired in patients with PPV during balance tasks at the limits of postural control.

Effects on the location of the centre of gravity and the foot pressure contribution to standing balance associated with ageing

The aim was to analyse the limitation of the head and lumbar movements in relation to the centre of gravity which is needed to maintain standing balance with ageing. The participants of the study were 25 healthy volunteers divided into two age categories, the young group (mean 22.4 +/- 2.7 years) and the elderly group (mean 71.2 +/- 3.6 years). The instruments for measuring the movements of the lumbar region and head and the centre of pressure (COP) were a 3-D motion analysis system and a force plate. In addition, the peak foot pressure was measured during standing using the F-Scan system. The participants were first asked to stand relaxed for 10 s. They then shifted from the starting position to the four directions of sway: anterior, posterior, right and left. They were asked to maintain standing balance at the maximal distance position for each sway as much as possible for 10 s. Analysis of parameters was performed by measuring the average maximal linear displacement (cm) of the head and lumbar markers, the COP (cm), and the peak foot pressure (% of body weight per cm2) in each participant. The data of the young group for lumbar maximal displacement were greater than those of the elderly group in the anterior, posterior and lateral sways. A significant difference between the young and elderly data was found in the posterior sway. According to the data of the head's maximal displacement, the elderly group's data were greater than the young group's data in all sways, except for the anterior side. For the data of peak foot pressure in the posterior sway, the elderly group's data was greater than the young group's data. The forefoot area data of the young group was significantly greater than that of the elderly group, and the heel area data of the elderly was significantly greater than that of the young group in the right sway. The results suggest that the maximal displacement of head and lumbar positions and the toe's muscle activity in the forefoot are important factors associated with the centre of gravity in elderly adults. It is postulated that each base of support area of the older adults in smaller than that of younger adults. These variables could be made available as a clinical test for the degree of poor balance.

Increased body sway at 3.5-8 Hz in patients with phobic postural vertigo

Postural sway during upright stance was analyzed in 12 patients with phobic postural vertigo (PPV) and in 12 age-matched healthy volunteers. Recordings were made under different conditions (with the eyes open or closed): when standing on a foam rubber pad with the head upright, turned 30 degrees to the right or left, or during 1 Hz horizontal head oscillations. Sway analysis included calculation of sway path, of root mean square values of sway and of the power spectrum of sway in fore/aft and lateral directions. There was a significant increase in sway activity in the 3.53-8 Hz frequency band in patients with PPV. This did not impair objective postural stability. Increase in higher frequency sway activity may simply reflect a change in postural strategy rather than a sensorimotor dysfunction. The patients' conscious control of stance may augment co-activation of anti-gravity muscles, a strategy applied by normal subjects when performing demanding balancing tasks.

Postural imbalance and vibratory sensitivity in patients with idiopathic scoliosis: implications for treatment

Sporadic research reports of decreased proprioception and balance problems have been reported in subjects with idiopathic scoliosis, yet these sensory motor deficits have not been addressed in conservative clinical management programs. The purpose of this study was to compare both balance reactions and vibratory sensitivity (as an estimate of proprioception) in patients with idiopathic scoliosis (N = 24) and age-matched controls (N = 24). Balance was measured by the ability to pass a series of simple static and complex sensory-challenged balance tasks. Vibratory thresholds were measured with the Bio-Thesiometer at the cervical spine, wrist, and foot. Compared with age-matched controls, regardless of curve severity or spinal fusion, the subjects with idiopathic scoliosis had similar simple static balance responses when the somatosensory system was stable (with or without vision or head turning), but they were significantly more likely to fail the complex, sensory-challenged balance tasks when the somatosensory system was challenged by an unstable position of the feet, particularly when the eyes were closed. The vibratory thresholds were similar in subjects with scoliosis and their age-matched controls, but individuals with moderate to severe scoliosis (> 25 degrees) had significantly higher vibratory thresholds than those with mild curves. These findings suggest there may be problems with postural righting in patients with idiopathic scoliosis, particularly when the balance task challenges the vestibular pathways. Although vibration sensitivity did not distinguish normal healthy individuals from individuals with idiopathic scoliosis, those with more severe scoliotic curves appear to have a high threshold to vibration. These balance and vibratory differences could either be interpreted as etiologic risk factors or as consequences of spinal asymmetry. In either case, given that curves can continue to progress even into the adult years, improving the ability to right the body with gravity could help maintain the balance of the spine despite structural asymmetry.

Effects of diminished and conflicting sensory information on balance in patients with cerebellar deficits

We studied the effects of altered sensory information on standing balance in 25 patients with cortical cerebellar atrophy (CCA), nine patients with olivoponto-cerebellar atrophy (OPCA), and 10 normal subjects. The total sway path and its components, the anteroposterior (AP) sway path and the lateral sway path, were measured under six conditions: (1) standing on a fixed platform with the eyes open and visual surroundings fixed, (2) standing on a fixed platform with the eyes closed, (3) standing on a fixed platform with the eyes open and visual surroundings AP sway referenced, (4) standing on an AP sway-referenced platform with the eyes open and visual surroundings fixed, (5) standing on an AP sway-referenced platform with the eyes closed, and (6) standing on an AP sway-referenced platform with the eyes open and visual surroundings AP sway referenced. Patients swayed more than normal subjects during normal stance (condition 1), when the visual information was absent (condition 2) or distorted (condition 3), and when the proprioceptive information from the ankles was distorted (condition 4). Patients swayed much more than normal, and most fell, when two sensory modalities were affected under condition 5 (proprioceptive information distorted and visual information absent) and condition 6 (both proprioceptive information and visual information distorted). When the patients' sway was normalized to that of the first condition, however, only their lateral sway was greater than the sway in normal subjects. Unlike in normal subjects, the patients' lateral sway varied with the AP sway to approximately the same degree in each condition for conditions 1-5. Clinical ratings of gait and balance were highly correlated with the sway measures. Quantitative testing of standing balance with altered sensory information has better sensitivity than normal stance testing.

Head stabilization in peripheral vestibular syndromes

In classical posturography the standing position has been evaluated by recording the postural sway on a force-plate and measuring some parameters such as surface and velocity (Platform or P-recording). The postural sway not only results in forces exerted on the support surface by the feet, but the head also participates in the movements of this postural sway. For recording of the head movements (H-recording), a lightbulb is placed on top of the head and the described light-path is recorded by a TV camera. Such an H-recording can be achieved simultaneously with the platform-recording. A comparative study indicates that, for some patients differences could be found between H- and P-recordings, for others not. The H-recording, in fact, gives information about the stabilization of the head, compared with the stability on the platform (P-recording). The importance of the information furnished by the double recording in Static Posturography type IV (SPGIV) can be deduced from the number of patients showing one or more differences between the types of recording. Nearly 70% showed a difference in at least one test. In fact, 55% showed it in two or more tests. In half of the tests, considered separately, a difference was noted. The differences observed provide complementary information in this combined recording. If the H-recording were to be used as a separate technique, it has to be born in mind that the results are certainly not always the same as when using P-recording, as in classical posturography.