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PubMed1997

Anticipatory postural adjustments during standing in below-the-knee amputees.

OBJECTIVE: We studied the role of adaptive changes within the central nervous system in anticipatory postural adjustments seen in unilateral below-the-knee amputees. DESIGN: Changes in electromyographic and mechanical variables were compared during standardized tasks performed by standing subjects. BACKGROUND: Anticipatory postural adjustments represent an important mechanism of postural control which was expected to be changed in amputees because of both mechanical and secondary, neurological reasons. METHODS: Six patients after a below-the-knee amputation and six control subjects stood on a force platform and performed fast bilateral shoulder movements and also dropped or caught a load from (into) extended hands. Anticipatory changes in the background activity of postural muscles were analysed. RESULTS: In amputees, there were cases of marked asymmetry in anticipatory changes of the background muscle activity which were larger on the intact side of the body but were commonly small or absent on the side of the amputation. This asymmetry could lead to larger mediolateral forces and displacements of the centre of pressure. CONCLUSIONS: We suggest that asymmetrical patterns of anticipatory postural adjustments reflect central adaptive changes secondary to the amputation. Rehabilitation approaches would benefit from understanding and taking advantage of the adaptive changes within the central nervous system. RELEVANCE: We demonstrated asymmetries in patterns of anticipatory postural adjustments during voluntary arm movements and load manipulations by standing unilateral amputees. This finding is of potential importance for rehabilitation of amputees and their prosthetic training.

Journal Article↗

PubMed1996

Measures of postural steadiness: differences between healthy young and elderly adults.

Measures of postural steadiness are used to characterize the dynamics of the postural control system associated with maintaining balance during quiet standing. The objective of this study was to evaluate the relative sensitivity of center-of-pressure (COP)-based measures to changes in postural steadiness related to age. A variety of time and frequency domain measures of postural steadiness were compared between a group of twenty healthy young adults (21-35 years) and a group of twenty healthy elderly adults (66-70 years) under both eyes-open and eyes-closed conditions. The measures that identified differences between the eyes-open and eyes-closed conditions in the young adult group were different than those that identified differences between the eye conditions in the elderly adult group. Mean velocity of the COP was the only measure that identified age-related changes in both eye conditions, and differences between eye conditions in both groups. The results of this study will be useful to researchers and clinicians using COP-based measures to evaluate postural steadiness.

Adult↗

PubMedDate not supplied

Clinical evaluation of a new biofeedback standing balance training device.

For patients with neurological damage of the central nervous system, such as that due to cerebrovascular accident (CVA), standing balance training is a critical therapeutic procedure to be undertaken before walking and self-care training. The identification and characterization of neurological disorder in postural steadiness will enhance our understanding of the postural control system, and help to identify patients at risk of falls in the CVA population. This paper discusses the design and clinical evaluation of a new biofeedback training device for static (postural steadiness) performance of the standing balance system. The device includes a height adjustable standing table, an instrumented force sensing platform, an on-line weight bearing audio/visual biofeedback system, a postural correction mirror, and a belt suspension system for the upper extremities. A quantitative evaluation protocol of bilateral asymmetries in weight distribution and postural sway to characterize standing balance with the force sensing platform is discussed. Finally, the clinical evaluation results of sixty patients with hemiplegia from acute stroke for a period of four weeks are discussed. With this economic standing training device, the static standing steadiness can be trained effectively through weight bearing biofeedback and a postural correction mirror in the clinical and home caring environments.

Adult↗

PubMed1989

Stance dependence of automatic postural adjustments in humans.

This study investigated the effect of initial stance configuration on automatic postural responses in humans. Subjects were tested in both bipedal and quadrupedal stance postures. The postural responses to horizontal translations of the supporting surface were measured in terms of the forces at the ground, movement of the body segments, and electromyographic (EMG) activity. Postural responses to the same perturbations changed with initial stance posture; these responses were biomechanically appropriate for restoring centre of mass. A change in stance configuration prior to platform movement led to a change in both the spatial and temporal organization of evoked muscle activation. Specifically, for the same direction of platform movement, during bipedal stance muscles on one side of the lower limb were activated in a distal to proximal sequence; during quadrupedal stance, muscles on the opposite side of the lower limb were activated and in a proximal to distal sequence. The most significant finding was an asymmetry in the use of the upper limbs and the lower limbs during postural corrections in quadrupedal stance. Whereas antagonists of the upper limb were either co-activated or co-inhibited, depending on the direction of translation, lower limb antagonists were reciprocally activated and inhibited. Human subjects in a quadrupedal stance posture used the lower limbs as levers, protracting or retracting the hips in order to propel the trunk back to its original position with respect to the hands and feet. Postural responses of the subjects during quadrupedal stance were remarkably similar to those of cats subjected to similar perturbations of the supporting surface. Furthermore, the same predominance of lower limb correction is characteristic of both species, suggesting that the standing cat is a good model for studying postural control in humans.

Adult↗

PubMed2004

Nociceptive EMG suppression in triceps brachii muscle in humans.

OBJECTIVE: Inhibitory spinal reflexes in human hand muscles mediated by cutaneous afferents (=cutaneous silent periods, CSPs) serve to protect the hand from injury. Proximal muscles are included in a complex protective pattern implementing both excitatory and inhibitory reflexes. METHODS: We investigated the functional organization of CSPs in the triceps brachii muscle (TB) - the prime elbow extensor - assessing different stimulus intensities and elbow positions. Thirteen healthy subjects underwent recurrent electrical index finger tip stimulation with different intensities while volitionally activating TB against resistance. The rectified and averaged electromyogram (EMG) was recorded from TB with surface electrodes while the elbow joint was held in full flexion, full extension, and at an angle of 90 degrees. RESULTS: Digit II stimulation resulted in distinct CSPs in TB. Increasing stimulus intensities caused a more profound EMG suppression. Different elbow positions had a significant influence on CSP onset and end latency, and duration. CONCLUSIONS: The present findings are consistent with a functional organization of protective reflexes in the proximal human upper limb across several metameric segments. Spinal inhibitory neurons serving to rapidly suppress basic muscle synergies may compete with neural circuitry involved in postural control.

Adult↗

PubMed1996

Relationship between frequency of upside-down posture and space size around upside-down catfish, Synodontis nigriventris.

The catfish Synodontis nigriventris shows a unique habit taking a stable upside-down posture in free water regardless of an above, one-sided illumination. This upside-down posture can be observed when the catfish is apart from objects because the catfish usually orients its ventral side towards the water bottom or objects due to a so-called ventral substrate response. Thus, it is not easy to study the mechanism of the upside-down posture. To resolve this problem, the frequency of the upside-down posture was measured by using various sizes of vessel in which the catfish was kept. Video analysis showed that the frequency of the upside-down posture depended on the space size around the catfish. The smaller the size became, the higher the frequency of the upside-down posture became. Furthermore, the frequency of the upside-down posture depended on the shape of the vessel bottom. Curved-bottom vessels induced the upside-down posture more frequently than flat bottom. These findings suggest that a small, curved-bottom vessel is ideal for researching the upside-down postural control mechanism.

Animals↗

PubMed2004

Reciprocal influences of attentional focus on postural and suprapostural task performance.

The authors examined the influence that attentional focus on either a postural or a suprapostural task had on the performance of each task. Participants (N = 32) stood on an inflated rubber disk and held a pole horizontally. All participants performed under 4 attentional focus conditions: external (disk) or internal (feet) focus on the postural task, and external (pole) or internal (hands) focus on the suprapostural task. Compared with internal focuses, external focuses on either task resulted in similar and reduced postural sway. Response frequency on each task increased when participants focused on the respective task. Finally, an external focus on either task produced higher frequencies of responding on the suprapostural task. The authors conclude that suprapostural task goals have a stronger influence on postural control than vice versa, reflecting the propensity of the motor system to optimize control processes on the basis of the desired movement effect.

Attention↗

PubMed2006

The effects of balance training on gait late after stroke: a randomized controlled trial.

OBJECTIVE: To investigate the effects of balance training, using force platform biofeedback, on quantitative gait characteristics of hemiparetic patients late after stroke. DESIGN: Randomized, controlled, assessor-blinded trial. SETTING: Rehabilitation ward and gait laboratory of a university hospital. SUBJECTS: Forty-one patients (mean (standard deviation; SD) age of 60.9 (11.7) years) with hemiparesis late after stroke (median time since stroke six months) were randomly assigned to an experimental or a control group. INTERVENTIONS: The control group (n = 19) participated in a conventional stroke inpatient rehabilitation programme, whereas the experimental group (n = 22) received 15 sessions of balance training (using force platform biofeedback) in addition to the conventional programme. MAIN OUTCOME MEASURES: Selected paretic side time-distance, kinematic and kinetic gait parameters in sagittal, frontal and transverse planes were measured using a three-dimensional computerized gait analysis system, one week before and after the experimental treatment programme. RESULTS: The control group did not show any statistically significant difference regarding gait characteristics. Pelvic excursion in frontal plane improved significantly (P = 0.021) in the experimental group. The difference between before-after change scores of the groups was significant for pelvic excursion in frontal plane (P = 0.039) and vertical ground reaction force (P = 0.030) in favour of experimental group. CONCLUSION: Balance training using force platform biofeedback in addition to a conventional inpatient stroke rehabilitation programme is beneficial in improving postural control and weight-bearing on the paretic side while walking late after stroke.

Biofeedback, Psychology↗

PubMed1981

Some contributions of touch, pressure and kinesthesis to human spatial orientation and oculomotor control.

Human spatial orientation and oculomotor control are under multimodal influence. It is not possible in the normal animal to stimulate differentially the vestibular receptors without activating other receptor systems whose activity may have a profound influence on postural control and experienced orientation. Many patterns of behavior and response that have been attributed solely to vestibular function are actually dependent wholly or in part on touch, kinesthetic, and proprioceptive stimulation.

Eye Movements↗

PubMed2005

How the eyes move the body.

The increased postural sway of patients with disorders of the vestibular system improves with vision. The suppression of pathologic nystagmus also reduces sway. Because the latter effect cannot be attributed to retinal slip as a relevant feedback for postural control, the authors investigated how eye movements rather than retinal slip affect balance. They found that slow eye movements increase sway, possibly by an efference copy, which explains why spontaneous nystagmus causes postural imbalance.

Adult↗

PubMed1989

Injections of a beta-adrenergic antagonist in pontine reticular structures modify the gain of vestibulospinal reflexes in decerebrate cats.

1. The norepinephrine (NE)-containing locus coeruleus (LC) neurons control posture as well as the gain of the vestibulospinal reflexes either through direct coeruleospinal (CS) projections or by inhibiting the dorsal pontine reticular formation (pRF) and the related medullary inhibitory reticulospinal (RS) system. The question whether these inhibitory influences on the pRF are mediated through beta-adrenoceptors was investigated by injecting in precollicular decerebrate cats small doses of the non-selective beta-adrenergic antagonist propranolol in different pontine tegmental structures. 2. Injection of propranolol (usually 0.25 microliters at the concentration of 4.5 micrograms/microliters of saline) in dorsal pontine structures, which decreased the tonic contraction of limb extensors ipsilateral to the side of the injection, greatly increased the amplitude of the multiunit EMG responses of the ipsilateral triceps brachii to roll tilt of the animal at 0.15 Hz, +/- 10 degrees. Correspondingly, the response gain of the forelimb extensor to labyrinth stimulation increased. Moreover, a slight decrease in phase lead of the responses was observed. These responses were always characterized by an increased EMG activity during ipsilateral tilt and a decreased activity during contralateral tilt, as shown in the control records (alpha-responses). The same injection also produced in some instances an increase of the extensor tonus of the contralateral limbs, associated with an increased EMG activity of the contralateral triceps brachii; on the other hand, the amplitude of modulation and thus the response gain of this muscle to the same parameters of labyrinth stimulation decreased, while the response pattern reversed (beta-responses), thus being opposite to that displayed by the triceps brachii ipsilateral to the side of the injection. 3. The changes in posture and reflexes described above appeared 10-20 min after unilateral injection of propranolol in the pRF, reached in highest values in about 60-100 min and persisted for more that three hours before returning to the control level. These effects were not due to irritative phenomena following injection of the fluid, since neither changes in posture nor in the response gain of the triceps brachii to labyrinth stimulation were observed after injection of an equal volume of saline in the pRF of that side. Moreover, the magnitude of the effects increased to some extent in relation to the dose of the beta-adrenergic blocker. 4. Histological controls indicated that the structure responsible for these postural and reflex changes was located in the dorsal pontine tegmental region immediately ventral to the LC and included the peri-LC alpha and the surrounding dorsal pRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2006

The "posture second" strategy: a review of wrong priorities in Parkinson's disease.

Falls are common in Parkinson's disease. It remains difficult to predict these falls, presumably because clinical balance tests assess single components of postural control, whereas everyday fall mechanisms are typically more complicated. A substantial proportion of everyday falls appears to occur while Parkinson patients attempt to perform multiple tasks at the same time. Furthermore, little attention is generally paid to the possible contribution of cognitive impairments to falls. The importance of mental dysfunction is supported by the fact that cognitive loading while walking or balancing can lead to marked deteriorations in postural performance, and there is some evidence to suggest that such "dual tasking" is particularly difficult for elderly persons with dementia or depression. We examined what strategies Parkinson patients used when a basic walking task became increasingly challenging by adding additional tasks (both motor and cognitive). Most patients could perform a simple "dual task" test: simultaneously walking and answering simple questions. However, as the walking task became more complex, patients' performance began to deteriorate. Interestingly, this was reflected not only by failure to answer questions, but also by an increasing number of blocks in motor performance (walking and balancing). This behaviour was different from that of both young and elderly controls, who appeared to sacrifice performance on the cognitive task in order to optimise their gait and balance ("posture first" strategy). Preliminary evidence suggest that impaired multiple task performance is associated with a two-fold increased risk of sustaining falls in daily life. We conclude that Parkinson patients are less inclined than healthy persons to maintain a safe gait. Instead, Parkinson patients use a "posture second" strategy and treat all elements of a complex task with equal priority, which in daily life may go at the expense of maintaining balance and lead to falls.

Accidental Falls↗

PubMed2006

Voluntary and involuntary postural responses to imposed optic flow.

We demonstrated that postural responses to imposed optic flow are to some extent voluntary. In a moving room, participants either stood normally or were instructed to resist any influence of visible motion on their stance. When participants attempted to resist, coupling of body sway with motion of the room was significantly greater than when the eyes were closed, but was significantly reduced relative to coupling in the normal stance condition. The results indicate that the use of imposed optic flow for postural control is not entirely automatic or involuntary. This conclusion motivates a search for non-perceptual factors that may influence the degree to which body sway is coupled to imposed optic flow.

Adolescent↗

PubMed2002

Modifications of vestibular responses of individual reticulospinal neurons in lamprey caused by unilateral labyrinthectomy.

A postural control system in the lamprey is driven by vestibular input and maintains the dorsal-side-up orientation of the animal during swimming. After a unilateral labyrinthectomy (UL), the lamprey continuously rolls toward the damaged side. Normally, a recovery of postural equilibrium ("vestibular compensation") takes about 1 mo. However, illumination of the eye contralateral to UL results in an immediate and reversible restoration of equilibrium. Here we used eye illumination as a tool to examine a functional recovery of the postural network. Important elements of this network are the reticulospinal (RS) neurons, which are driven by vestibular input and transmit commands for postural corrections to the spinal cord. In this study, we characterized modifications of the vestibular responses in individual RS neurons caused by UL and the effect exerted on these responses by eye illumination. The activity of RS neurons was recorded from their axons in the spinal cord by chronically implanted electrodes, and spikes in individual axons were extracted from the population activity signals. The same neurons were recorded both before and after UL. Vestibular stimulation (rotation in the roll plane through 360 degrees ) and eye illumination were performed in quiescent animals. It was found that the vestibular responses on the UL-side changed only slightly, whereas the responses on the opposite side disappeared almost completely. This asymmetry in the bilateral activity of RS neurons is the most likely cause for the loss of equilibrium in UL animals. Illumination of the eye contralateral to UL resulted, first, in a restoration of vestibular responses in the neurons inactivated by UL and in an appearance of vestibular responses in some other neurons that did not respond to vestibular input before UL. These responses had directional sensitivity and zones of spatial sensitivity similar to those observed before UL. However, their magnitude was smaller than before UL. Second, the eye illumination caused a reduction of the magnitude of vestibular responses on the UL side. These two factors tend to restore symmetry in bilateral activity of RS neurons, which is the most likely cause for the recovery of equilibrium in the swimming UL lamprey. Results of this study are discussed in relation to the model of the roll control system proposed in our previous studies as well as in relation to the vestibular compensation.

Action Potentials↗

PubMed2006

Changing control strategies during standard assessment using computerized dynamic posturography with older women.

The goal of this investigation was to explore the use of spectral analysis to examine the data obtained during computerized dynamic posturography (CDP). In particular, we examined whether spectral analysis would provide more detailed information about underlying postural control strategies and potential learning across conditions and trials of the sensory organization test (SOT). Twenty older women between the ages of 60 and 72 (mean=65.2) were assessed using standard testing protocol. Participants showed significant improvements from the first to the second trials in their equilibrium scores in the more difficult conditions. This finding was reflected in the spectral analysis data by a shift in the frequency distribution towards greater power in the lower frequency range. This frequency change likely reflects a change in the ankle strategy used to maintain balance during the more difficult conditions.

Aged↗

PubMed1980

Development of the brain stem in the rat. III. Thymidine-radiographic study of the time of origin of neurons of the vestibular and auditory nuclei of the upper medulla.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational days 12 and 13 (E12 + 13) until the day before parturition (E21 + 22). In adult progeny of the injected rats the proportion of neurons generated on specific embryonic days was determined quantitatively in the vestibular and auditory nuclei of the upper medulla. In the vestibular nuclei, neurons are generated between days E11 and E15 in an overlapping sequential order, yielding a lateral-to-medial and a rostral-to-caudal internuclear gradient. In the lateral vestibular nucleus peak production time is day E12; in the superior nucleus, E13; in the inferior nucleus, E13 and E14; and in the medial nucleus, E14. The early generation of neurons of the lateral vestibular nucleus may reflect the early differentiation of the circuit from the gravity receptors (utricle) to neurons of the spinal cord controlling postural balance. The later production of neurons of the superior vestibular nucleus may reflect the subsequent differentiation of the circuit from the rotational receptors (semicircular canals) to the neurons of the brain stem controlling eye movements. The generation time of neurons of the nucleus prepositus hypoglossi overlaps with that of the medial vestibular nucleus. The neurons of the anteroventral and posteroventral cochlear nuclei are produced from days E13 to E17, with no temporal differences between the two nuclei. The neurons of the dorsal cochlear nucleus are generated over a very long time span, beginning on day E12 and extending into the postnatal period. There is a sequence in the production of neurons forming the different layers of the dorsal cochlear nucleus in the following order: pyramidal cells, cells of the inner layer, cells of the outer layer and, finally, cells of the granular layer. There is also a sequential production of neurons in four nuclei of the superior olivary complex. In the lateral trapezoid nucleus peak production time is day E12; in the medial superior olivary nucleus, day E13; in the medial trapezoid nucleus, day E15; and in the lateral superior olivary nucleus, day E16. This order yields a medial-to-lateral gradient in the dorsal aspect of the superior olivary complex, and a lateral-to-medial gradient ventrally. These mirror-image gradients were also seen intranuclearly in the lateral superior olivary nucleus and the medial trapezoid nucleus. The cytogenetic gradients could not be related to tonotopic representation; however, they could be related to the lateral location of ipsilateral cochlear nucleus input to the lateral superior olivary nucleus and the medial location of the contralateral cochlear nucleus input to the medial trapezoid nucleus.

Animals↗

PubMed1993

Ontogenesis of head stabilization in space during locomotion in children: influence of visual cues.

The main purpose of this study was to investigate the development of the head stabilization in space strategy (HSSS) during various locomotor tasks in 3- to 8-year-old children and adults. The contribution of visual factors to the HSSS was also examined by applying peripheral visual restriction, stroboscopic visual motion cue restriction, and darkness. The kinematics of the head and trunk rotations (pitch, yaw, and roll) were analyzed by means of an optical TV-image processor (ELITE system). For each of the three angular components, an appropriate "head anchoring index" was defined in order to compare the HSSS with a head stabilization on the trunk strategy. Head-trunk correlation rates were also calculated for each angular component in order to evaluate the head-trunk stiffness. The development of head-trunk coordinations during locomotion under normal vision can be said to involve at least three main periods. The first period occurs from the age of 3 to 6 years, when the HSSS is adopted only while walking on the flat ground. While walking on narrow supports, children in this age-group rather tend to increase the head-trunk stiffness, especially at 6 years of age. The second period includes 7- to 8-year-old children. Children of this age become able to adopt the HSSS while walking on narrow supports. During this period, the HSSS is associated with a large decrease in the head-trunk correlations. Lastly, in adulthood the HSSS is commonly adopted but specifically involves the roll component associated with the lateral body oscillations while walking. Vision was found to have little influence on children's HSSS while walking, whatever their age. Moreover, darkness induces an increase in the efficiency of the HSSS in adults. This confirms that the HSSS is the most appropriate strategy available for dealing with an increase in the level of equilibrium difficulty and may reflect a "top-down" organization of the postural control while walking. These results also suggest that the HSSS may be mainly of vestibular origin and presumably serves to facilitate the visual input processing, particularly that of the motion and peripheral visual cues which are involved in the control of body equilibrium during locomotion.

Adult↗

PubMed2006

Spectrally similar periodic and non-periodic optic flows evoke different postural sway responses.

The present study investigated the effect of optic flow periodicity on postural sway. Head and center-of-pressure (COP) displacements in response to an oscillating full-field bullseye-and-checkerboard pattern were recorded in six healthy adults. Scene movement was driven by one of five signals: (1) 0.1 Hz sinusoid, (2) 0.3 Hz sinusoid, (3) 0.5 Hz sinusoid, (4) the periodic sum of these three sinusoids (PSUM), or (5) a non-periodic counterpart (NPSUM = 0.1+ pi/10 + 0.5 Hz). Sway response power at the various stimulus frequencies were compared: (1) among the three pure sinusoidal groups; and (2) between the two sum-of-sinusoid groups. Head and COP responses displayed similar spectral content, though sway magnitude was larger for the head. Sway responses to the moving scenes were significantly larger than those observed during quiet stance. Each sinusoidal moving scene evoked a strong response at the stimulus frequency, as well as increased sway at non-stimulus frequencies, primarily below 0.2 Hz. For the sum-of-sinusoids stimuli, both PSUM and NPSUM signals elicited sway responses at each of their component frequencies. The amplitudes of these responses were similar to one another at 0.1 and 0.3 Hz, but significantly different at 0.5 Hz, with PSUM responses on average four times larger than those for NPSUM. These findings indicate that spectrally similar periodic and non-periodic stimuli elicit quantitatively different sway responses. The observed behaviors may be due to postural sensitivity to the predictability of visual motion, or due to other nonlinear and/or time-varying mechanisms in the postural control system.

Adult↗