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PubMedDate not supplied

Effect of head orientation on human postural stability following unilateral vestibular ablation.

Effective interpretation of vestibular inputs to postural control requires that orientation of head on body is known. Postural stability might deteriorate when vestibular information and neck information are not properly coupled, as might occur with vestibular pathology. Postural sway was assessed in unilateral vestibulopathic patients before and acutely, 1, 4, and 18+ months after unilateral vestibular ablation (UVA) as well as in normal subjects. Postural equilibrium with eyes closed was quantified as scaled pk-pk sway during 20 s trials in which the support surface was modulated proportionally with sway. Subjects were tested with the head upright and facing forward, turned 45 degrees right, and 45 degrees left. Equilibrium was uninfluenced by head orientation in normal subjects. In contrast, patients after UVA showed both a general reduction in stability and a right/left head orientation-dependent asymmetry. These abnormalities adaptively recovered with time. It is concluded that vestibular inputs to postural control are interpreted within a sensory-motor context of head-on-body orientation.

Adolescent↗

PubMed1983

Motor control. How posture and movements are governed.

This article is a review of the nature of motor control: the abilities and limitations of the body, the principles of doing and learning, how parts of the nervous system interact, and how information is processed to generate the blend of sensory, perceptive, and motor functions that we call motor control. The relation to physical therapy is stressed: PT is regarded as an emerging applied science of motor control, and motor control is regarded as a basic science of physical therapy.

Brain↗

PubMed1997

Driving skills after whiplash.

Previous studies have shown that some persons with longlasting problems after whiplash have changed eye movements. These changes have been related to disturbance of the posture control system. The question raised in the present study is whether such disturbances can influence daily life functions connected with balance, position and external movements, such as car driving. A group of 23 persons with disturbed eye movements due to whiplash injury, was tested in a driving simulator, together with a closely matched control group. The results revealed significant differences between the two groups with respect to response times to the traffic signs presented, identification of type of sign, as well as steering precision while the subjects' attention was directed to the process of identifying the signs. Alternative explanations such as driving experience, pain, medication or malingering are at least partly controlled for, but cannot completely be ruled out. A distorted posture control system leading to disturbance of eye movements seems to be the most likely primary causative factor, but these disturbances are most certainly complexly determined. Reduced attention capacity is considered to be a mediating secondary factor. Registration of eye movements may be a useful diagnostic tool to evaluate driving skill after whiplash.

Adult↗

PubMedDate not supplied

Effects of foot orthoses on patients with chronic ankle instability.

Chronic instability of the ankle can be the result of mechanical and functional deficits. An acute ankle sprain can cause mechanical and functional instability, which may or may not respond to standard rehabilitation programs. Chronic instability results when there is persistent joint laxity of the ankle or when one or more components of neuromuscular control of the ankle are compromised. A loss of balance or postural control seems to be the most consistent finding among athletes with chronic instability of the ankle. Recent research in patients with acute and chronic ankle instability has revealed positive effects of foot orthoses on postural control. This article reviews the current research relevant to the use of foot orthoses in patients with chronic ankle instability and clarifies the suggested benefits and the shortcomings of these investigations.

Ankle Joint↗

PubMed1997

System identification of closed-loop cardiovascular control: effects of posture and autonomic blockade.

We applied system identification to the analysis of fluctuations in heart rate (HR), arterial blood pressure (ABP), and instantaneous lung volume (ILV) to characterize quantitatively the physiological mechanisms responsible for the couplings between these variables. We characterized two autonomically mediated coupling mechanisms [the heart rate baroreflex (HR baroreflex) and respiratory sinus arrhythmia (ILV-HR)] and two mechanically mediated coupling mechanisms [the blood pressure wavelet generated with each cardiac contraction (circulatory mechanics) and the direct mechanical effects of respiration on blood pressure (ILV-->ABP)]. We evaluated the method in humans studied in the supine and standing postures under control conditions and under conditions of beta-sympathetic and parasympathetic pharmacological blockades. Combined beta-sympathetic and parasympathetic blockade abolished the autonomically mediated couplings while preserving the mechanically mediated coupling. Selective autonomic blockade and postural changes also altered the couplings in a manner consistent with known physiological mechanisms. System identification is an "inverse-modeling" technique that provides a means for creating a closed-loop model of cardiovascular regulation for an individual subject without altering the underlying physiological control mechanisms.

Adult↗

PubMed2005

Trunk sway in patients with spinocerebellar ataxia.

We investigated whether quantified measurements of trunk sway during stance and gait tests in patients with autosomal dominant spinocerebellar ataxia (SCA) could be a useful approach to assess ataxia, which is highly relevant for adequate follow-up and future intervention studies. Examined were 11 SCA patients and 11 age-matched, healthy controls. Postural and balance control were quantified using peak-to-peak measurements of trunk angle and angular velocity, in the roll (lateral) and pitch (anterior-posterior) directions, during a battery of stance and gait tasks. In all stance tasks, trunk angle displacement and angular velocity in both the pitch and roll planes were significantly larger in the SCA group compared with the control group. Among the ataxia patients instability was more increased in the pitch than in the roll direction for two-legged stance tasks, especially when standing on foam, with pronounced oscillations in the pitch plane at 1.4 and 2.5 Hz. A similar dominance of pitch over roll instability was also observed in most gait tasks, especially for tandem gait and while walking with simultaneous head rotations. Trunk sway measurements were effective in detecting and quantifying the gait and balance abnormalities in SCA patients, suggesting that this method might be used for follow-up studies of SCA patients. Furthermore, the method might help to identify early symptomatic individuals and those patients at risk of falling. The postural instability in SCA was found to be multidirectional, although there is generally more pitch than roll instability corresponding with predominant involvement of the spinocerebellum.

Adult↗

PubMed2002

Vestibulospinal control of posture.

To better understand the role of the vestibular system in postural coordination, we compared the ability of subjects with complete, bilateral loss of vestibular function and age-matched control subjects to maintain equilibrium and postural orientation during sinusoidal displacements of the support surface at a variety of frequencies. We also examined the ability of visual or somatosensory-light touch information to substitute for missing vestibular information in dynamic postural coordination. The results suggest that vestibular information is used as a gravitational reference frame to prevent slow drift of the trunk in space during complex postural tasks. Furthermore, visual information or somatosensory information from light touch of a finger on a stable reference can significantly substitute for loss of vestibular function.

Gravitation↗

PubMed1985

Patients with an acoustic neurinoma examined with a tilting room.

Patients with acoustic neurinomas do not usually show vertigo or spontaneous nystagmus, suggesting a gradual decrease of vestibular function with adequate compensation. Seventeen patients with acoustic neurinoma were examined to test their postural control. Examination in the tilting room showed a visual dominance in postural control with these patients irrespective of involvement of the central vestibular system. The subjective horizon was determined in addition to routine audiovestibular examination, to be informed about the compensation process. When routine audiovestibular examination points to an acoustic neurinoma, a pathological subjective horizon favours the diagnosis, although this is not mandatory. The combination of tilting room and stabilometry is superior in detecting visual dominance to the standard Romberg test.

Humans↗

PubMed2006

Distance impairs postural stability only under binocular viewing.

Prior studies indicate that postural stability under binocular viewing is not better than under monocular viewing. This was tested at the distances of 145 cm [Fox, C.R. (1990). Some visual influences on human postural equilibrium: binocular versus monocular fixation. Perception and Psychophysics, 47 (5), 409-422] and 90 cm [Isotalo, E., Kapoula, Z., Feret, P.H., Gauchon, K., Zamfirescu, F., & Gagey, P.M. (2004). Monocular versus binocular vision in postural control. Auris Nasus Larynx, 31 (1), 11-17]. On the other hand, postural stability is known to decrease with distance increase. We re-examined the effect of binocular versus monocular viewing on postural stability at near and far distances (40 and 200 cm), and for both young (25.7+/-2.7 years), and old subjects (61.2+/-4.6 years). For both groups of subjects, proximity decreased the area of CoP, the standard deviation of antero-posterior sway (SDy) and the variance of speed. The group of elderly presented increased variance of speed at far distance in comparison with young subjects. The novel finding is the interaction between distance and viewing condition. Under binocular viewing, the area of CoP was significantly higher at far distance than at near; in contrast, monocular viewing produced similar CoP values at both distances. Increased instability at far distance when both eyes are viewing is attributed to decreased sensitivity to binocular disparity cues and to visual motion in depth resulting from body sway. Monocular viewing would provide similar stability at far and at near distance, because sensitivity to lateral visual motion, detected monocularly, decreases less with distance than sensitivity to binocularly detected motion in depth. Alternatively, such monocular viewing could increase subject's attention and lead to tighter postural control regardless of the distance.

Adult↗

PubMed1987

Stability of the head: studies in normal subjects and in patients with labyrinthine disease, head tremor, and dystonia.

The dynamics of postural control of the head were investigated in normal human subjects and patients with neurological disease. The technique adopted was to measure the head movements provoked by passive, unpredictable oscillations of the trunk in the frequency range 0-6-7 Hz when subjects were required (a) to try to stabilise their head "in space" and (b) to try to make their heads move "en bloc" with the trunk. Head movement responses were characterised by the gain and phase with respect to trunk movement (transfer function) and degree of linear relationship between head and trunk (coherence). The normal transfer function approximated a cascade of two second-order, underdamped, systems representing the passive inertial, viscous, and elastic properties of the muscle and joints of the head and neck. Stabilisation of the head "in space" produced about 40% reduction in transmission of body movement, was only evident at frequencies less than 1 Hz and was affected partly by voluntary movements. An alabyrinthine patient could also achieve some spatial stabilisation. The findings indicate a weak role for vestibular-collic reflexes and emphasise that the primary control of head posture during unpredictable movement is through the tonic visco-elastic properties of neck muscles that work to stabilise the head on the shoulders. In patients with dystonia of the neck and essential and cerebellar head tremor, the head showed a tendency to unstable oscillation (resonance). The instability and dystonia could be measured in terms of visco-elastic constants and damping ratios. The head movements of some tremor patients did not linearly follow the trunk movement, showing that the motion stimulus provoked abnormal phasic muscle activity at frequencies other than those of the tremor. The technique quantifies head control in movement disorders and is sensitive to abnormal function.

Adolescent↗

PubMed2004

Measurement of balance in survivors of acute lymphoblastic leukemia in childhood.

Survivors of acute lymphoblastic leukemia (ALL) in childhood have been identified with balance problems. The goals of this study were to objectively quantify these observations by measuring the displacement and velocity of the body centre of pressure, a measure of 'sway'. The subjects included 79 ALL survivors who were at least 1 year post-treatment for ALL and 83 age-matched controls. Testing was carried out using various static balance tests designed to challenge central nervous system maintenance of balance and postural control. Patients were different from controls, across all age groups, in the more difficult task in which they were required to balance over a narrow base of support. However this did not reach statistical significance. When they were asked to perform this task with their eyes closed 32% of the patients tested, as opposed to 2% of controls, were unable to complete the task (significant at P<0.01, chi(2)). The youngest group of patients (children aged 5-7 years) presented consistently with lower (or similar) displacement and lower velocity measures. This phenomenon has been observed in healthy children, however, in patients, these trends were magnified and beyond the normal age range in healthy children. The velocity values were significantly different from the other patient groups (normalized values for velocity; P<0.01). These observations then manifested as higher sway values when patients were challenged with a difficult task with their eyes closed. We propose that survivors of childhood ALL have delayed motor development compared to age-matched controls giving rise to impairment in balance and postural control. It is possible that these impairments are a consequence of intensive multi-agent chemotherapy and cranial irradiation.

Adolescent↗

PubMed2000

Paraspinal muscle response to electrical vestibular stimulation.

Galvanic (electrical) vestibular stimulation (GVS) has been used to study the role of the vestibular system in postural control by inducing postural sway in standing subjects. The purpose of this study was to determine the timing and pattern of activation in the paraspinal muscles in response to GVS and to compare these responses with those in the muscles of the lower leg. Binaural-bipolar GVS was applied to the skin overlying the mastoid processes of 10 subjects while they stood on a force plate with their eyes closed. The stimulus consisted of a 0.6 mA 5-pulse sequence. Each pulse lasted for 2 s, followed by 4 s of rest. The centre of pressure (COP) vs. time for each trial was calculated from the reaction forces and moments. Surface electromyographic (EMG) signals from the paraspinal and gastrocnemius muscles were recorded bilaterally. The EMG signals were rectified and integrated (iEMG). The iEMG from the muscles on the cathodal side of the body were then subtracted from the iEMG of the anodal side muscles, to yield a differential EMG (dEMG). Both the paraspinal and gastrocnemius muscles became activated in response to the stimulus. The pattern of activation was consistent with the changes observed in the centre of pressure. The primary response in both muscles acted to move the body toward the anode. This primary response began at 74 +/- 20 ms in the paraspinal muscles and at 118 +/- 18 ms in the gastrocnemius. A second component of the response began at 232 +/- 27 ms in the paraspinal muscles and 262 +/- 54 ms in the gastrocnemius muscles. This second phase of the response was opposite in direction to the primary response and was responsible for decelerating the body and maintaining the deviated position of the centre of mass over the base of support. Following the termination of the stimulus, the opposite pattern of muscle activation in both the paraspinal and the gastrocnemius muscles was observed. The results of this study suggest that the paraspinal muscles may play a significant role in the frontal plane response to vestibular stimulation during stance in humans.

Adult↗

PubMed1993

The Cascade Neural Network Model and a Speed-Accuracy Trade-Off of Arm Movement.

We propose a hybrid neural network model of aimed arm movements that consists of a feedforward controller and a postural controller. The cascade neural network of Kawato, Maeda, Uno, and Suzuki (1990) was employed as a computational implementation of the feedforward controller. This network computes feedforward motor commands based on a minimum torque-change criterion. If the weighting parameter of the smoothness criterion is fixed and the number of relaxation iterations is rather small, the cascade model cannot calculate the exact torque, and the hand does not reach the desired target by using the feedforward control alone. Thus, one observes an error between the final position and the desired target location. By using a fixed weighting parameter value and a limited iteration number to simulate target-directed arm movements, we found that the cascade model generated a planning time-accuracy trade-off, and a quasi-power-law type of speed-accuracy trade-off. The model provides a candidate neural mechanism to explain the stochastic variability of the time course of the feedforward motor command. Our approach also accounts for several invariant features of multijoint arm trajectories, such as roughly straight hand paths and bell-shaped speed profiles.

Journal Article↗

PubMed2005

Widespread access to predictive models in the motor system: a short review.

Recent behavioural and computational studies suggest that access to internal predictive models of arm and object dynamics is widespread in the sensorimotor system. Several systems, including those responsible for oculomotor and skeletomotor control, perceptual processing, postural control and mental imagery, are able to access predictions of the motion of the arm. A capacity to make and use predictions of object dynamics is similarly widespread. Here, we review recent studies looking at the predictive capacity of the central nervous system which reveal pervasive access to forward models of the environment.

Brain↗

PubMed1993

The effects of background visual roll stimulation on postural and manual control and self-motion perception.

The effects of background visual roll stimulation on postural control, manual control, and self-motion perception were investigated in this study. In the main experiment, 8 subjects were exposed to wide field-of-view background scenes that were tilted and static, continuously rotating, or sinusoidally rotating at frequencies between 0.03 and 0.50 Hz, as well as a baseline condition. The subjects performed either a postural control task (maintain an upright stance) or a manual control task (keep an unstable central display horizontally level). Root-mean square (RMS) error in both the postural and manual control tasks was low in the static tilt condition and extremely high in response to continuous rotation. Although the phases of the postural and manual responses were highly similar, the power and RMS error generated by the sinusoidal visual background stimulation peaked at a lower frequency in the postural task. Vection ratings recorded at the end of the postural and manual trials somewhat paralleled the frequency tuning differences between tasks, which a subsequent experiment showed to be the result of the differential motion of the central display rather than the differential positioning of the subject. In general, these results show that the dynamic characteristics of visual orientation systems vary according to the specific motor and/or perceptual system investigated.

Adult↗

PubMed2000

Can the control of bodily orientation be significantly improved in a group of older adults with a history of falls?

OBJECTIVE: To determine the short-term effectiveness of a biofeedback-based, computerized intervention that applied the principles of the ecological theory of perception and control of bodily orientation to the rehabilitation of older adults with a history of falling. PARTICIPANTS: Forty-five older adults (X = 78.5 years) with a history of falls were assigned to either a control (n = 21) or intervention group (n = 24). DESIGN: A 2 x 2 (Group x Time) mixed factorial design with repeated measures on the second factor. SETTING: A motor control research laboratory in a university setting. MEASUREMENT: Impairments in multiple dimensions of balance (i.e., dynamic postural control and sensory organization) were measured before and after an 8-week balance intervention using the 100% Limits of Stability Test and Sensory Organization Test. More functional limitations in balance and/or mobility were measured using two clinical tests: Berg Balance Scale and Timed Up and Go test. MAIN RESULTS: Repeated measures multivariate analyses and follow-up testing indicated significant improvements in the dynamic balance and sensory integration capabilities in the case of the intervention group only (P < .03). Significant improvements were also observed in the two clinical measures of balance and mobility evaluated before and after the intervention for the intervention group only. CONCLUSIONS: Theory-driven rehabilitation programs that focus on manipulating individual, task, and environmental constraints concurrently can significantly improve the control of bodily orientation of older adults with a previous history of falls in both static and dynamic action environments. Moreover, the significant improvements in functional performance observed for the intervention group suggest that interventions emphasizing task-specific practice are not the only means by which an older adult's ability to perform daily activities requiring postural control can be improved.

Accidental Falls↗

PubMed2005

Body sway during quiet standing: is it the residual chattering of an intermittent stabilization process?

This paper reviews different approaches for explaining body sway while quiet standing that directly address the instability of the human inverted pendulum. We argue that both stiffness control [Winter, D. A., Patla, A. E., Riedtyk, S., & Ishac, M. (2001). Ankle muscle stiffness in the control of balance during quiet standing. Journal of Neurophysiology, 85, 2630-2633] and continuous feedback control by means of a PID (Proportional, Integral, Derivative) mechanism [Peterka, R. J. (2000). Postural control model interpretation of stabilogram diffusion analysis. Biological Cybernetics, 83, 335-343.] can guarantee asymptotic stability of controlled posture at the expense of unrealistic assumptions: the level of intrinsic muscle stiffness in the former case, and the level of background noise in the latter, which also determines an unrealistic level of jerkiness in the sway. We show that the decomposition of the control action into a slow and a fast component (rambling and trembling, respectively, as proposed by [Zatsiorsky, V. M., & Duarte, M. (1999). Instant equilibrium point and its migration in standing tasks: Rambling and trembling components of the stabilogram. Motor Control, 4, 185-200; Zatsiorsky, V. M., & Duarte, M. (2000). Rambling and trembling in quiet standing. Motor Control, 4, 185-200.]) is useful but must be modified in order to take into account that rambling is not a stable equilibrium trajectory. We address the possibility of a form of stability weaker than asymptotic stability in light of the intermittent stabilization mechanism outlined by [Loram, I. D., & Lakie, M. (2002a). Human balancing of an inverted pendulum: position control by small, ballistic-like, throw and catch movements. Journal of Physiology, 540, 1111-1124.], and propose an indicator of intermittent stabilization that is related to the phase portrait of the human inverted pendulum. This indicator provides a further argument against the plausibility of PID-like control mechanisms. Finally, we draw attention to the sliding mode control theory that provides a useful theoretical framework for formulating realistic intermittent, stabilization models.

Adult↗

PubMed1995

Changes in motor cortex activity during reaching movements with similar hand paths but different arm postures.

1. Neuronal activity was recorded in the motor cortex of a monkey that performed reaching movements with the use of two different arm postures. In the first posture (control), the monkey used its natural arm orientation, approximately in the sagittal plane. In the second posture (abducted), the monkey had to adduct its elbow nearly to shoulder level to grasp the handle. The path of the hand between targets was similar in both arm postures, but the joint kinematics and kinetics were different. 2. In both postures, the activity of single cells was often broadly tuned with movement direction and static arm posture over the targets. In a large proportion of cells, either the level of tonic activity, the directional tuning, or both, varied between the two postures during the movement and target hold periods. 3. For most directions of movement, there was a statistically significant difference in the direction of the population vector for the two arm postures. Furthermore, whereas the population vector tended to point in the direction of movement for the control posture, there was a poorer correspondence between the direction of movement and the population vector for the abducted posture. These observed changes are inconsistent with the notion that the motor cortex encodes purely hand trajectory in space.

Animals↗