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PubMed1999

[Postural balance following stroke: towards a disadvantage of the right brain-damaged hemisphere].

In the light of studies published in the last ten years, we have suspected a differential influence of the sides of hemispheric cerebral lesions on posture and balance. A study was aimed at verifying this hypothesis, the method of which being original because many possible confounding factors such as age, sex as well as topography and size of the brain lesion have been taken into account in the statistical analysis. Inclusion criteria were: right-handed patients, first stroke, no previous disease which might have affected balance. Their postural abilities (ranging from 0 to 36) were assessed 90 +/- 3 days after stroke onset on a clinical scale. This clinical assessment was used here because it could be easily performed in all patients, irrespective of the severity of their impairment. Lesion locations were determined using the Atlas by Talairach and Tournoux and the number of cerebral areas altered gave an estimation of the lesion size. The first fifty patients consecutively admitted to rehabilitation and responding to the inclusion criteria were thus examined (25 with a right and 25 with a left hemispheric lesion; 14 women and 36 men; mean age 57.2 = yrs). The main result was lower postural performances in right brain-damaged patients than in left brain damaged patients (21.5 vs 29.4; p = 0.01). Postural abilities were also inversely related to age (r = -0.28; p = 0.04), lesion size (r = -0.41; p = 0.003) and were lower in women than in men (22.1 vs 28.8; p = 0.02). This study therefore confirms the existence of a right hemispheric dominance for postural control. The existence of inverse correlation between postural abilities and the number of omitted targets in cancellation task on one hand (r = -0.63, p < 0.001), the ipsilesional bias in line bissection on the other hand (r = -0.36; p = 0.01), argued for a relationship between the main result of this study and the well known cerebral organization of spatial information processing, based on a right hemisphere dominance for spatial attention and/or representation. The 'postural neglect' concept is discussed.

Aged↗

PubMed2026

Dual-tasking reveals severity-dependent reorganization of cortical beta energy landscapes in Parkinson's disease.

Dual-task impairment is a hallmark of Parkinson's disease (PD), yet the large-scale neural mechanisms underlying postural-motor interference remain poorly understood. In particular, it is unclear how cortical network dynamics reorganize across disease severity when postural control competes with concurrent task demands. This study investigated EEG-derived beta-band cortical energy landscapes in healthy older adults, early-stage PD, and mid-stage PD during single- and dual-task conditions. Dual-task behavioral cost increased with disease severity for concurrent manual performance (p < 0.001), whereas a quadratic pattern was observed for postural performance. Energy landscape analysis revealed severity-dependent reconfiguration of cortical beta dynamics. Dual-task-related landscape changes in effective network flexibility (ΔNeff), landscape geometry (ΔEvar and ΔGmag), and dominant low-energy attractor organization (ΔLow mass and ΔLow area) showed significant monotonic trends (p < 0.05), reflecting progressive constrained cortical network dynamics with advancing PD severity. In addition, dual-task-related landscape alterations were associated with clinical severity, as indexed by Hoehn and Yahr stage (|r| = 0.353-0.423, p = 0.016-0.048), and showed associations with motor impairment, as measured by MDS-UPDRS part III scores (|r| = 0.333-0.455, p = 0.009-0.063). These findings demonstrate that dual-task demands induce severity-dependent reconfiguration of cortical beta energy landscapes in PD. Energy landscape geometry may capture systems-level neural constraints associated with dual-task susceptibility in PD, providing a physiologically grounded framework to characterize disease-related functional vulnerability.

Humans↗

PubMed2002

Multisensory fusion and the stochastic structure of postural sway.

We analyze the stochastic structure of postural sway and demonstrate that this structure imposes important constraints on models of postural control. Linear stochastic models of various orders were fit to the center-of-mass trajectories of subjects during quiet stance in four sensory conditions: (i) light touch and vision, (ii) light touch, (iii) vision, and (iv) neither touch nor vision. For each subject and condition, the model of appropriate order was determined, and this model was characterized by the eigenvalues and coefficients of its autocovariance function. In most cases, postural-sway trajectories were similar to those produced by a third-order model with eigenvalues corresponding to a slow first-order decay plus a faster-decaying damped oscillation. The slow-decay fraction, which we define as the slow-decay autocovariance coefficient divided by the total variance, was usually near 1. We compare the stochastic structure of our data to two linear control-theory models: (i) a proportional-integral-derivative control model in which the postural system's state is assumed to be known, and (ii) an optimal-control model in which the system's state is estimated based on noisy multisensory information using a Kalman filter. Under certain assumptions, both models have eigenvalues consistent with our results. However, the slow-decay fraction predicted by both models is less than we observe. We show that our results are more consistent with a modification of the optimal-control model in which noise is added to the computations performed by the state estimator. This modified model has a slow-decay fraction near 1 in a parameter regime in which sensory information related to the body's velocity is more accurate than sensory information related to position and acceleration. These findings suggest that: (i) computation noise is responsible for much of the variance observed in postural sway, and (ii) the postural control system under the conditions tested resides in the regime of accurate velocity information.

Adult↗

PubMed2004

[Standing stability in children- and young adults. Influence of proprioceptive, visual and vestibular systems in age- and sex dependent changes].

BACKGROUND: The maintenance of balance while standing is ensured by means of a sensory motor control system. As the development of sensory organization on posture control in children is not clear at this time, the aim of this study was to analyse the significance of each sensory component in relation to age and sex. SUBJECTS AND METHOD: A total of 128 children between the ages of 3 and 16 years and 23 adults were examined using the Sensory Organization Test (EquiTest). RESULTS: Age-related changes during the test procedure showed a developmental tendency of the sensory motor process. The influence of the proprioceptive function on stance stability seemed to be completely developed between 3-4 years. The visual and vestibular afferences reached the adult level between 15-16 years with differences between girls and boys. CONCLUSION: Age-related evaluation of the postural mechanisms can be used for differentiation between physiological and pathological results in balance control as well as for monitoring therapy progress in the context of, for example, hyperactivity or learning disability.

Adaptation, Physiological↗

PubMed2005

Center of pressure measures during standing tasks in minimally impaired persons with multiple sclerosis.

BACKGROUND AND PURPOSE: Balance impairments are common in persons with multiple sclerosis (MS), but clinical balance tests may not detect subtle deficits in adults with MS who are not yet experiencing functional limitations or disability. The purpose of this study was to determine if center of pressure (COP) displacement during standing tasks could be a useful performance-based evaluative measure for adults with MS who have minimal or no balance deficits on clinical examination using the Berg Balance Scale (BBS). SUBJECTS AND METHODS: Twenty-one adults with MS were compared with 21 age- and gendermatched healthy adults. Subjects with MS were tested with the BBS, Mini-mental State Exam, Expanded Disability Status Scale (EDSS), and Multiple Sclerosis Functional Composite (MSFC). They also performed voluntary leaning and reaching movements while kinematic and kinetic data were collected. Control subjects performed the same tasks with the exception of the EDSS and MSFC. RESULTS: COP displacement during reaching and leaning was less in adults with MS when compared to control subjects. There were no differences in anthropometric, kinematic, or foot position variables that could account for this difference. Furthermore, there was no difference between groups when COP displacement during reaching was expressed as a percentage of the maximum COP displacement during leaning. DISCUSSION AND CONCLUSION: COP measures show clear differences when comparing healthy adults with minimally impaired adults with MS. The lack of between-group differences when COP displacement during reaching was expressed as a percentage of the maximum COP displacement during leaning suggests that the subjects with MS adopt a reaching strategy that allows them to stay within their reduced limits of stability. COP measures during standing tasks appear well-suited to quantifying changes in postural control over time or in response to intervention for minimally impaired persons with MS.

Adult↗

PubMed1989

The time course of postflight simulator sickness symptoms.

Reports of posteffects following training sessions in Navy and Army flight simulators were obtained from pilots to determine the time course of recovery from simulator sickness. Results imply that posteffects may be a more serious problem than previously considered; 45% of all those queried (N greater than 700) reported having experienced symptoms of simulator sickness; 25% of the symptoms lasted more than 1 h after leaving the simulator; and 8% lasted more than 6 h. Postexposure symptoms were classified into three categories: visuomotor (based on disturbances in oculomotor control; e.g., eyestrain), disorientation (based on disturbance in postural control; e.g., dizziness), and nausea (vagal/autonomic symptoms). A safety risk may be posed particularly by the moderately high frequency of symptoms involving postural disequilibrium. Guidelines for coping with risks are discussed.

Adaptation, Psychological↗

PubMed1999

Effect of facilitation of sensation from plantar foot-surface boundaries on postural stabilization in young and older adults.

BACKGROUND: One of the more pervasive effects of aging is loss of cutaneous sensation, which appears to correlate with impaired postural control and increased risk of falling. This study examined the potential for compensating for the destabilizing effects of reduced cutaneous sensitivity by placing a raised edge underneath the perimeter of the plantar foot surface, so as to facilitate sensation from the stability boundaries of the base of support. METHODS: The main experiment involved 14 healthy older adults (aged 65-73) selected because they were known, from a previous study, to have moderate plantar cutaneous insensitivity. We also report results of an initial experiment involving 7 healthy young adults (aged 23-31). In both experiments, we studied effects of the plantar facilitation on control of rapid stepping reactions evoked by unpredictable postural perturbation, applied via sudden platform movement in forward, backward, and lateral directions. We also studied effects on "feet-in-place" responses evoked by continuous pseudorandom platform motion in mediolateral and anteroposterior directions. Subjects were blindfolded in all tests. RESULTS: Plantar facilitation reduced the incidence of "extra" limb movements, beyond the initial step, during forward-step reactions in the older adults. There also appeared to be an improved ability to control feet-in-place reactions: young subjects were better able to recover balance without stepping when falling backward (given instructions to "try not to step"), and both young and older subjects reduced the extent to which the center of foot pressure approached the posterior foot boundary during continuous anteroposterior platform motion. CONCLUSIONS: This study provides evidence that mechanical facilitation of sensation from the boundaries of the plantar surface of the foot can improve the efficacy of certain types of stabilizing reactions evoked by unpredictable postural perturbation. The results may be directly transferable to the design of special footwear insoles to reduce instability and risk of falling in older adults.

Adult↗

PubMed2001

Human balance control during cutaneous stimulation of the plantar soles.

Previous work on human postural control of upright stance, performed in the absence of visual and vestibular orientation cues, suggests that somatosensory cues in the feet enable subjects to maintain equilibrium during low-frequency platform tilts. Here we confirm earlier studies which indicated that stimulation of plantar cutaneous mechanoreceptors can lead to postural responses. Yet, this stimulation did not modify considerably the postural reactions of normal subjects and vestibular loss patients during platform tilts. We therefore suggest that it is necessary to differentiate between (i) cues from plantar cutaneous receptors involved in exteroceptive functions, like the evaluation of the support structure or of relative foot-to-surface motion, and (ii) cues from deep receptors which subserve proprioceptive functions like the control of center of pressure shifts within the limits of the foot support base.

Adult↗

PubMed1993

A kinematic and electromyographic analysis of the development of sitting posture in infants.

This study was designed to describe the development of posture control in sitting in response to a natural perturbation. Seven normal infants 2 to 5 months of age were tested at two stages of independent sitting development. Trunk support was removed from infants while sitting erect and the postural responses were videotaped and EMG recorded from the upper trunk extensors, lumbar paraspinals, gluteus maximus, rectus femoris, hamstrings, and abdominals. Kinematic variables (trunk displacement, trunk velocity, trunk curvature) and an EMG variable (pattern of muscle activation) were analyzed with computer programs. Between Stages 1 and 2 of sitting development, anterior trunk displacement and velocity decreased significantly, although the trunk extension curve did not change significantly. Infants had variable muscle responses during Stage 1; however, during Stage 2 EMG analysis revealed less variability and the emergence of postural synergies. Overall, lumbar paraspinals, hamstrings, and quadriceps were the muscles most frequently active during the postural response. Each subject had a preferred synergy, with the most common synergies being a lumbar paraspinal-hamstring synergy and a lumbar paraspinal-quadriceps synergy. These data provide evidence that trunk displacement and trunk velocity decrease in infants develop independent sitting posture, and these variables may be used to measure improvement in sitting control. We suggest that the control of sitting posture is related to the emergence and preferred use of the paraspinal-hamstring and paraspinal-quadriceps synergies.

Age Factors↗

PubMed2005

[Towards a better understanding and quantitative assessment of pushing, a postural behaviour caused by some strokes].

INTRODUCTION: Postural control aims to build up and align the body orientation (posture) and stabilize body segments. The existence of two separate mechanisms, one for the control of body orientation with respect to gravity and one for its stabilisation, is an emerging concept that allows a better understanding of postural disorders, including pushing, after stroke. Objectives. - Literature review concerning pushing, one of the most puzzling postural behaviours after stroke. METHODS: Critical review of papers indexed in Medline and book chapters dealing with pushing. RESULTS: There is no agreement about the definition of pushing: some authors consider that pushers push himself toward the paretic side using the healthy arm or leg; others consider that pushers lean (list) toward the side opposite the lesion and resist any attempt to become more upright. Surprisingly, the push itself has never been measured. Some ordinal scales have been recently proposed, but their psychometric properties have not been analysed. These methodological insufficiencies explain in part the disagreements about frequency (from 5% to 50% of patients with stroke) and cause(s) of pushing. CONCLUSION: Pushing may be the most dramatic clinical manifestations of an extreme bias in the construction of the biological vertical. We argue for a better assessment of vertical perception/representation after stroke involving the three modalities of the biological (subjective) vertical: the visual vertical, the haptic or tactile vertical, and especially the postural vertical.

Functional Laterality↗

PubMed2006

Effects of abdominal muscle fatigue on anticipatory postural adjustments associated with arm raising.

Anticipatory postural adjustments (APAs) are postulated to ameliorate the effects of the disturbance to posture caused by voluntary movement. The primary hypothesis tested in our study was that the magnitude of anticipatory trunk muscle activity is altered by abdominal muscle fatigue. A subsidiary aim of the present study was to examine the directional nature of APAs and use this information to elucidate the central or peripheral nature of changes in postural muscle activity associated with abdominal muscle fatigue. The present study was a within subject design, where abdominal muscle fatigue was induced by a static abdominal curl. Surface EMG was used to assess postural muscle activity in the following trunk muscles; rectus abdominis, erector spinae and internal oblique. Following abdominal muscle fatigue, the magnitude of muscle activity during APAs was significantly reduced by 20% in both the rectus abdominis (fatigued muscle) and the erector spinae (not fatigued) indicating a central rather than peripheral fatigue effect on muscle activity. Abdominal muscle fatigue also induced a 30% increase in the baseline muscle activity of the internal oblique. The changes in magnitude of APA muscle activity may reflect a change in system gain or a change in postural control perhaps related to a change in perceived postural stability. An increase in baseline muscle activity in the internal oblique may compensate partially for the reduction in APAs.

Abdominal Muscles↗

PubMed2006

Comparison of quantitative analysis and fractal analysis of center of pressure based on muscle fatigue.

To examine the influence of muscle fatigue on center of pressure displacement during quiet standing using quantitative and fractal analyses, 12 healthy young men and women did the exercise stress test on the triceps surae muscle until fatigued. Subjects were measured for body stability for 60 sec. before and after the exercise. Quantitative analysis showed that center-of-pressure parameters for distance, velocity, amplitude distribution, and mean vector length of sway in the anterior/posterior direction changed significantly after muscle fatigue but not on the periodic parameters. This result suggested that quantitative analysis may identify the effects of muscle fatigue on the parameters that show displacement in the anterior/posterior direction of center of pressure. Fractal analysis indicated the value of critical point coordinates increased after muscle fatigue. This analysis can clarify the fundamental postural control strategy and time-series characteristics of postural sway which cannot be identified by spectral analysis.

Adult↗

PubMed2005

Dynamic stabilometric findings in equilibrium disorders of the elderly.

Equilibrium disorders are frequent symptoms of aging, both on account of the so-called "multisensorial decay" and age-related diseases. Aim of the study was to evaluate the functional integrity of static-dynamic postural control related subsystems (visual, somatosensorial, vestibular), the fundamental postural strategies effected and adaptation to destabilizing inputs, in elderly subjects with otoneurological disorders. From January to November 2003, 40 elderly patients (19 male, 21 female, mean age +/- SD: 69.5 +/- 4.3 years; range: 65-83), with balance disorders, consisting in dizziness or vertigo, have been observed. Otoneurologic and internal case history was collected in all patients, all of whom were submitted to otoscopy, otoneurologic examination, pure-tone audiometry, as well as a specific examination called Equi test. The sensorial analysis, as often occurs in elderly subjects without unbalance, revealed marked impairment of the somatosensorial (85%), compared to vestibular (60%) and visual (40%), subsystems. Longer latencies of motor responses to forward platform translations than to backward translations were observed, even if the symmetry of movements was more evident in the former. Postural adaptation was more frequently impaired during raising of the support (70%) than during lowering. Therefore, in elderly people, somatosensorial impairment, combined with flexor muscle dysfunction, exists. Indeed, extensor responses, although slower than flexor responses, are more correctly performed.

Aged↗

PubMed1986

Dynamic posture analysis of Spacelab-1 crew members.

Dynamic posture testing was conducted on the science crew of the Spacelab-1 mission on a single axis linear motion platform. Tests took place in pre- and post-flight sessions lasting approximately 20 min each. The pre-flight tests were widely spaced over the several months prior to the mission while the post-flight tests were conducted over the first, second, fourth, and sixth days after landing. Two of the crew members were also tested on the day of landing. Consistent with previous postural testing conducted on flight crews, these crew members were able to complete simple postural tasks to an acceptable level even in the first few hours after landing. Our tests were designed to induce dynamic postural responses using a variety of stimuli and from these responses, evaluate subtle changes in the postural control system which had occurred over the duration of the flight. Periodic sampling post-flight allowed us to observe the time course of readaptation to terrestrial life. Our observations of hip and shoulder position, when subjected to careful analysis, indicated modification of the postural response from pre- to post-flight and that demonstrable adjustments in the dynamic control of their postural systems were taking place in the first few days after flight. For transient stimuli where the platform on which they were asked to stand quickly moved a few centimeters fore or aft then stopped, ballistic or open loop 'programs' would closely characterize the response. During these responses the desired target position was not always achieved and of equal importance not always properly corrected some 15 seconds after the platform ceased to move. The persistent observation was that the subjects had a much stronger dependence on visual stabilization post-flight than pre-flight. This was best illustrated by a slow or only partial recovery to an upward posture after a transient base-of-support movement with eyes open. Postural responses to persistent wideband pseudorandom base-of-support translation were modeled as time invarient linear systems arrived at by Kalman adaptive filter techniques. Derived model parameters such as damping factor and fundamental frequency of the closed loop system showed significant modification between pre- and post-flight. This phenomenon is best characterized by movement of the poles toward increasing stability. While pre-flight data tended to show shoulders and hips moving in phase with each other, post-flight data showed a more disjoint behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗

PubMed2004

Postural and locomotor control in normal and vestibularly deficient mice.

We investigated how vestibular information is used to maintain posture and control movement by studying vestibularly deficient mice (IsK-/- mutant). In these mutants, microscopy showed degeneration of the cristae of the semicircular canals and of the maculae of the utriculi and sacculi, while behavioural and vestibulo-ocular reflex testing showed that vestibular function was completely absent. However, the histology of Scarpa's ganglia and the vestibular nerves was normal in mutant mice, indicating the presence of intact central pathways. Using X-ray and high-speed cineradiography, we compared resting postures and locomotion patterns between these vestibularly deficient mice and vestibularly normal mice (wild-type and IsK+/-). The absence of vestibular function did not affect resting posture but had profound effects on locomotion. At rest, the S-shaped, sagittal posture of the vertebral column was the same for wild-type and mutant mice. Both held the head with the atlanto-occipital joint fully flexed, the cervico-thoracic junction fully flexed, and the cervical column upright. Wild-type mice extended the head and vertebral column and could walk in a straight line. In marked contrast, locomotion in vestibularly deficient mice was characterized by circling episodes, during which the vertebral column maintained an S-shaped posture. Thus, vestibular information is not required to control resting posture but is mandatory for normal locomotion. We propose that vestibular inputs are required to signal the completion of a planned trajectory because mutant mice continued rotating after changing heading direction. Our findings support the hypothesis that vertebrates limit the number of degrees of freedom to be controlled by adopting just a few of the possible skeletal configurations.

Animals↗

PubMed1997

Home exercise to improve strength and walking velocity after hip fracture: a randomized controlled trial.

OBJECTIVE: To determine the effect of a home exercise program on strength, postural control, and mobility following hip fracture. DESIGN: Randomized controlled trial of 1 month's duration. SETTING: Daily exercise carried out within the subjects' home environments. PARTICIPANTS: Forty-two people 64 to 94 years of age, 35 of whom were living independently in the community and 7 of whom were residing in institutional care. Subjects were recruited on average 7 months after a fall-related hip fracture and randomly allocated to either the intervention or the control group (n = 21 each). The groups were well matched in terms of medical conditions, medication use, disability, and activity levels. INTERVENTION: A "home-based" program of weight-bearing exercise established at a visit by a physiotherapist. MAIN OUTCOME MEASURES: Quadriceps strength, postural sway, functional reach, weight-bearing ability, walking velocity, and self-rated fall risk. The subjects undertook these assessments at the beginning and end of the trial. RESULTS: At pretest, exercisers and controls performed similarly in all tests. At the end of the trial, the intervention group showed significantly greater quadriceps strength in the affected (hip-fractured) leg and increased walking velocity. The intervention subjects also improved their weight-bearing ability and reported reduced subjective falls risk. In contrast, there were no significant improvements in any of the test measures in the controls. Within the intervention group, improvements in quadriceps strength were significantly associated with improved performances in the weight-bearing test measures and with increased walking velocity. CONCLUSIONS: This exercise program improved strength and mobility following hip fracture. Further research is needed to ascertain whether the extent of this improvement in these fall risk factors is sufficient to prevent falls.

Aged↗

PubMed1997

Sensory representation in the cerebellum and control circuits of motion.

The role of the cerebellum in motion and posture control as deduced from the behaviorial effects of lesions has long been known. Subsequent recording and tracing studies in mammals yielded a cerebellar sensory representation featuring 'animalculi', not unlike those seen in the cerebral cortex. This image of cerebellar representation had to be revised with the demonstration of the 'fractured somatotopy' in somatosensory projections (Welker, 1987). A point in case is the trigeminal representation in the mammalian cerebellum, which still lacks a functional explanation. While a fractured somatotopy--if present--has yet to be demonstrated in birds, the topographical details of the trigeminal representation appear to vary considerably between and within both classes. This undoubtedly reflects the variety of functions trigeminocerebellar links subserve in the two classes, but is also indicative of species-specific cerebellar output variation. In this context the importance of cerebellar afferent topography for cerebellar function is discussed.

Animals↗

PubMed2004

The effect of a concurrent cognitive task on cortical potentials evoked by unpredictable balance perturbations.

BACKGROUND: Although previous studies suggest that postural control requires attention and other cognitive resources, the central mechanisms responsible for this relationship remain unclear. To address this issue, we examined the effects of altered attention on cortical activity and postural responses following mechanical perturbations to upright stance. We hypothesized that cortical activity would be attenuated but not delayed when mechanical perturbations were applied during a concurrent performance of a cognitive task (i.e. when attention was directed away from the perturbation). We also hypothesized that these cortical changes would be accompanied by alterations in the postural response, as evidenced by increases in the magnitude of anteroposterior (AP) centre of pressure (COP) peak displacements and tibialis anterior (TA) muscle activity. Healthy young adults (n = 7) were instructed to continuously track (cognitive task) or not track (control task) a randomly moving visual target using a hand-held joystick. During each of these conditions, unpredictable translations of a moving floor evoked cortical and postural responses. Scalp-recorded cortical activity, COP, and TA electromyographic (EMG) measures were collected. RESULTS: Results revealed a significant decrease in the magnitude of early cortical activity (the N1 response, the first negative peak after perturbation onset) during the tracking task compared to the control condition. More pronounced AP COP peak displacements and EMG magnitudes were also observed for the tracking task and were possibly related to changes in the N1 response. CONCLUSION: Based on previous notions that the N1 response represents sensory processing of the balance disturbance, we suggest that the attenuation of the N1 response is an important central mechanism that may provide insight into the relationship between attention and postural control.

Adult↗