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PubMed2003

Asymmetry in the pitch control system of the lamprey caused by a unilateral labyrinthectomy.

A postural control system in the lamprey is driven by vestibular input and maintains a definite orientation of the animal during swimming. After a unilateral labyrinthectomy (UL), the lamprey continuously rolls toward the damaged side. Important elements of the postural network are the reticulospinal (RS) neurons that are driven by vestibular input and transmit commands for postural corrections to the spinal cord. We characterized the effect of UL on vestibular responses in RS neurons elicited by rotation of the animal in the pitch plane. The activity of RS neurons was recorded from their axons in the spinal cord before and after UL. The neurons can be classified into the Up and Down groups activated preferentially with nose-up or nose-down rotation, respectively. After UL, vestibular responses in the group Up changed only slightly on the damaged side and disappeared almost completely on the opposite side. In the group Down, responses on both sides persisted after UL. These results indicate that the left and right subgroups of the group Up neurons receive excitatory input mainly from the contralateral labyrinth. In contrast, the group Down neurons receive excitatory input from both labyrinths. We conclude that the UL-induced changes in vestibular responses to pitch tilt will disturb the normal activity of the postural control system. The UL-induced asymmetry in the bilateral activity of the group Up neurons seems to be an important factor contributing to the loss of equilibrium in UL animals and to their rotation during swimming.

Animals↗

PubMed2006

Information processing capacity while wearing personal protective eyewear.

It is difficult to overemphasize the function vision plays in information processing, specifically in maintaining postural control. Vision appears to be an immediate, effortless event; suggesting that eyes need only to be open to employ the visual information provided by the environment. This study is focused on investigating the effect of Occupational Safety and Health Administration regulated personal protective eyewear (29 CFR 1910.133) on physiological and cognitive factors associated with information processing capabilities. Twenty-one college students between the ages of 19 and 25 years were randomly tested in each of three eyewear conditions (control, new and artificially aged) on an inclined and horizontal support surface for auditory and visual stimulus reaction time. Data collection trials consisted of 50 randomly selected (25 auditory, 25 visual) stimuli over a 10-min surface-eyewear condition trial. Auditory stimulus reaction time was significantly affected by the surface by eyewear interaction (F2,40 = 7.4; p < 0.05). Similarly, analysis revealed a significant surface by eyewear interaction in reaction time following the visual stimulus (F2,40 = 21.7; p < 0.05). The current findings do not trivialize the importance of personal protective eyewear usage in an occupational setting; rather, they suggest the value of future research focused on the effect that personal protective eyewear has on the physiological, cognitive and biomechanical contributions to postural control. These findings suggest that while personal protective eyewear may serve to protect an individual from eye injury, an individual's use of such personal protective eyewear may have deleterious effects on sensory information associated with information processing and postural control.

Adult↗

PubMedDate not supplied

Influence of arousal and attention on the control of postural sway.

Healthy young adults (n = 39) were asked to perform four different secondary cognitive tasks during quiet unperturbed stance, in order to investigate the influence of physiological arousal and attention distraction on the control of spontaneous postural sway. During each task, postural activity was quantified in terms of center-of-pressure displacement, leg-muscle activation, and ankle and hip rotation. Arousal was monitored via skin conductance, and questionnaires were used to assess state anxiety. Respiratory trunk movements were also recorded, to assess potential arousal-related destabilizing effects, but failed to show a strong association with the postural measures. The nature of the secondary task affected the postural responses in that subjects tended to lean slightly forward, and exhibited higher levels of activation in tibialis anterior, when performing a mental-arithmetic task. Although this task affected both attention and arousal, the leaning effect was limited to subjects who reported higher levels of anxiety-related autonomic or somatic symptoms during testing, and the degree of leaning was correlated with the level of physiological arousal. A secondary task that diverted attention but did not affect physiological arousal (listening to a spoken-word recording) failed to elicit changes in postural response. These findings suggest that the changes in leaning were associated with task-related changes in physiological arousal, and highlight the need to account for the potentially confounding influence of arousal when studying attentional effects. Given the potential influence on stability, the results also suggest that leaning should be monitored or controlled during balance assessment, particularly when dealing with individuals who may be anxious or afraid of falling.

Adult↗

PubMed2001

Study of a group of extremely preterm infants (25-27 weeks): how do they function at 1 year of age?

The functional outcome of 49 extremely preterm infants (gestational age: 25-27 weeks) was studied at the corrected age of 12 months. Apart from pediatric follow-up, a full neurologic assessment and the Bayley Motor and Mental Scales of Infant Development was done. Emphasis was placed on postural control, spontaneous motility, hand function, and elicited infantile reactions. Special attention was given to symmetric development. The infants were then categorized as having optimal or nonoptimal or asymmetric outcome. Overall, an optimal outcome was found in 19 infants (39%) and nonoptimal outcome in 30 infants (61%), 7 of whom failed on all domains of function. Postural control had a significant influence on the different domains of development such as motility (P < or = .001) and persistent infantile reactions (P < or = .001) and slightly less on hand function (P = .08) and asymmetry (P = .06). The outcome on spontaneous motility was significantly related to the results on infantile reactions (P < or = 005) and hand function (P = .05). Also, the score on the motor scale of the Bayley Developmental test was clearly related to outcome on spontaneous motility (P < or = .001) and reactions (P< or = .02). Abnormal brain ultrasonograms were related to the asymmetry of the infantile reactions (P < or = .05). Poor coordination of gross motor function will have consequences for appropriate visuomotor and sensorimotor integration, thereby hampering motor learning and later cognitive function, as is often described in preterm infants. It is suggested that the poor postural control found in many infants born preterm is the result of both myogenic and neurogenic deviations caused by the preterm birth and its nursing consequences.

Child Development↗

PubMed2005

Effects of the removal of vision on body sway during different postures in elite gymnasts.

The aim of this study was to analyse the effects of the removal of vision on postural performance and postural control in function of the difficulty and specificity of the posture. Twelve elite gymnasts were instructed to be as stable as possible with eyes open and eyes closed in three postures: bipedal, unipedal, and handstand ranked from the less difficult and less specific to the more difficult and more specific. The ratios eyes closed on eyes open, computed on CP surface and CP mean velocity, which respectively represents postural performance and postural control, were similar in the bipedal and handstand postures. They were highly increased in the unipedal one. The effect of the removal of vision and so the role of vision on body sway was not directly linked to the difficulty or specificity of the posture; other tasks' characteristics like the segments configuration also played a role.

Adolescent↗

PubMed2006

Age associated differences in postural equilibrium control: a comparison between EQscore and minimum time to contact (TTC(min)).

Increased postural instability and the subsequent elevation in fall incidence with increasing age are important contributors for hip fractures and developing frailty. When testing for such instability, most studies characterize balance in terms of center-of-mass (COM) deviation from a finite point, the "equilibrium point", located at the center of a subject's stance. For example, the clinically accepted equilibrium score (EQscore) represents instability as the maximum peak-to-peak sway about the "equilibrium point". An alternative theory views balance as being controlled within a "stability margin" in which all corrective actions are based on the time to contact (TTC) of the body's COM with that margin. This study examines the differences offered by evaluating balance control using the EQscore and TTC approach across several age groups and sessions. Consenting subjects from the Baltimore Longitudinal Study of Aging were recruited (N=155) from each age decade (20s-80s) who were generally healthy and free from neurological diagnoses. Results showed TTC tests detected significant variations in eyes open versus eyes closed testing that were unpredictable by EQscore. Further, TTC produced differences in age-related stability threats not seen using EQscore. The TTC data also provided a discriminating difference between subjects who fell in the difficult tests and those who maintained posture. Overall, these data suggest EQscore might not sufficiently account for dynamic control components the body may be using to maintain balance. TTC may offer a more accurate estimate of postural stability (functional ability) than EQscore based on its inclusion of a velocity component to detect dynamic changes.

Accidental Falls↗

PubMed2006

Posturographic stabilisation of healthy subjects exposed to full-length mirror image is inversely related to body-image preoccupations.

Affective states, anxiety in particular, have been shown to negatively influence human postural control efficiency as measured by posturographic means, while exposure to a full-length mirror image of one's body exerts a stabilizing effect. We tested the hypothesis that body image concerns and preoccupations would relate negatively to this stabilising effect. Sixty-six healthy students, who screened negative for psychiatric disorders, completed rating scales for anxiety, depression and body image concerns. Posturography recordings of body sway were taken under three conditions: with eyes closed, looking at a vertical bar and looking at a full-length mirror. The Eyes Open/Mirror Stabilometric Quotient [EOMQ=(sway path with eyes closed/sway path looking at the mirror)x100], an index of how much postural control is stabilized by mirror feedback in comparison to the visual vertical bar condition, was significantly inversely related to body image concerns and preoccupations, and to trait anxiety. This finding confirms the impact of emotional factors on human postural control, which warrant further studies. If confirmed in clinical populations characterized by high levels of body image disturbances, e.g. eating disorders, it could lead to developments in the assessment and monitoring of these patients.

Adult↗

PubMed1990

Early behavioral development in capuchins (Cebus).

Capuchin infants (genus Cebus) are born in a behaviorally more altricial state than is known for infants of other primate taxa except apes. Development in the first 2 months after birth is characterized by the major reorganization of sleeping and waking, assumption of postural control and the appearance of prehension. Capuchins develop postural control, prehension and locomotion later than do squirrel monkeys, baboons or macaques, presenting a pattern of motor development intermediate between these relatively more precocial genera and apes. Capuchins provide a useful model primate system in which to study development and its links with behavioral variability and life history.

Animals↗

PubMed1995

Vestibular stimulation perturbs human stance also at higher frequencies.

The effect of primary vestibular disturbance on postural control was investigated in 11 normal subjects exposed to perturbation by bi-polar binaural galvanic stimulation of the vestibular nerve. The stimulus consisted of 30 s of sinusoidal galvanic stimulation at frequencies of 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 3.0 and 4.0 Hz, with a current of +/- 1 mA, the subject standing with open or closed eyes and the response evoked being recorded with a force platform. As compared with resting values, i.e. no stimuli, variance of lateral body sway was significantly greater at all frequencies tested in the closed eyes condition and at frequencies of 0.2, 0.5, 1.0, 3.0 and 4.0 Hz in the open eyes condition; using a high pass filter with a cut-off frequency of 0.1 Hz, variance of lateral body sway was significantly greater at frequencies 0.2, 0.3, 0.5, 1.0 and 2.0 Hz in the closed eyes condition and at frequencies 0.5 and 2.0 Hz in the open eyes condition. These findings suggest that in the lateral plane vestibular input affects and probably contributes to human postural control over a wider frequency range than suggested by findings in previous studies. Moreover, the visual contribution appears to enable the subject to suppress vestibular input causing lateral body sway only in the lower frequency range (here at 0.2 and 0.3 Hz). This evidence of vestibular contribution to postural control in the lateral plane is consistent with the response characteristics of the vestibulo-ocular reflex.

Adolescent↗

PubMed1991

Optimal coordination and control of posture and locomotion.

This paper presents a theoretical model of stability and coordination of posture and locomotion, together with algorithms for continuous-time quadratic optimization of motion control. Explicit solutions to the Hamilton-Jacobi equation for optimal control of rigid-body motion are obtained by solving an algebraic matrix equation. The stability is investigated with Lyapunov function theory, and it is shown that global asymptotic stability holds. It is also shown how optimal control and adaptive control may act in concert in the case of unknown or uncertain system parameters. The solution describes motion strategies of minimum effort and variance. The proposed optimal control is formulated to be suitable as a posture and stance model for experimental validation and verification. The combination of adaptive and optimal control makes this algorithm a candidate for coordination and control of functional neuromuscular stimulation as well as of prostheses.

Algorithms↗

PubMed1995

Role of local nonspiking interneurons in the generation of rhythmic motor activity in the stick insect.

Local nonspiking interneurons in the thoracic ganglia of insects are important premotor elements in posture control and locomotion. It was investigated whether these interneurons are involved in the central neuronal circuits generating the oscillatory motor output of the leg muscle system during rhythmic motor activity. Intracellular recordings from premotor nonspiking interneurons were made in the isolated and completely deafferented mesothoracic ganglion of the stick insect in preparations exhibiting rhythmic motor activity induced by the muscarinic agonist pilocarpine. All interneurons investigated provided synaptic drive to one or more motoneuron pools supplying the three proximal leg joints, that is, the thoraco-coxal joint, the coxa-trochanteral joint and the femur-tibia joint. During rhythmicity in 83% (n = 67) of the recorded interneurons, three different kinds of synaptic oscillations in membrane potential were observed: (1) Oscillations were closely correlated with the activity of motoneuron pools affected; (2) membrane potential oscillations reflected only certain aspects of motoneuronal rhythmicity; and (3) membrane potential oscillations were correlated mainly with the occurrence of spontaneous recurrent patterns (SRP) of activity in the motoneuron pools. In individual interneurons membrane potential oscillations were associated with phase-dependent changes in the neuron's membrane conductance. Artificial changes in the interneurons' membrane potential strongly influenced motor activity. Injecting current pulses into individual interneurons caused a reset of rhythmicity in motoneurons. Furthermore, current injection into interneurons influenced shape and probability of occurrence for SRPs. Among others, identified nonspiking interneurons that are involved in posture control of leg joints were found to exhibit the above properties. From these results, the following conclusions on the role of nonspiking interneurons in the generation of rhythmic motor activity, and thus potentially also during locomotion, emerge: (1) During rhythmic motor activity most nonspiking interneurons receive strong synaptic drive from central rhythm-generating networks; and (2) individual nonspiking interneurons some of which underlie sensory-motor pathways in posture control, are elements of central neuronal networks that generate alternating activity in antagonistic leg motoneuron pools.

Action Potentials↗

PubMed1983

[Localization of the cortical representation of control of postural synergy in the frontal lobe of the brain].

Muscular activity of the legs and trunk was studied in 27 patients with verified tumours of the frontal lobes of the brain. It is shown that the abnormalities of the anticipated postural muscle activity are connected with the lesion of the median part of the premotor region. It is concluded that the supplementary motor area is concerned with the control of the postural synergy and involves the muscles of both sides of the body.

Brain Diseases↗

PubMedDate not supplied

Functional instability of the ankle and the role of neuromuscular control: a comprehensive review.

A review of current knowledge of the clinical syndrome of functional ankle instability is presented. Recent evidence has demonstrated that the majority of patients with functional instability of the ankle do not have mechanical hypermobility of the ankle joint. Functional instability of the ankle results from a loss of neuromuscular control. Components of neuromuscular control include proprioception, muscle strength, muscle reaction time, and postural control. Proprioceptive deficits lead to a delay in peroneal reaction time, which appears to be a peripheral reflex. Proprioception and eversion muscle strength improve with the use of passive supportive devices. Balance and postural control of the ankle appear to be diminished after a lateral ankle sprain and can be restored through training that is mediated through central nervous mechanisms. Methods of detecting deficits in neuromuscular control are presented along with rehabilitation techniques to treat functional instability of the ankle.

Ankle Injuries↗

PubMedDate not supplied

Proprioceptive and sensorimotor performance in Parkinson's disease.

We explored the effects of random whole-body vibration on leg proprioception in Parkinson's disease (PD). In earlier studies it was found that this treatment leads to improved postural control in these patients. Thus, one could speculate that these effects result from modified proprioceptive capabilities. Twenty-eight PD patients were subdivided in one experimental and one control group. Proprioceptive performance was analyzed using a tracking task basing on knee extension and flexion movements. Treatment consisted of 5 series of random whole-body vibration taking 60 seconds each. Control subjects had a rest period instead. Prominent over- and undershooting errors were found in both groups representing proprioceptive impairments. No significant differences became evident, however, either between pre- and post-tests or between experimental and control group. One might therefore conclude that spontaneous improvements in postural control are not directly connected with proprioceptive changes. Nevertheless, one also should keep in mind the general aspects and difficulties of analyzing proprioception.

Humans↗

PubMed2005

Random change in cortical load representation suggests distinct control of posture and movement.

Accurately maintaining a fixed limb posture and quickly moving between postures underlies both everyday skills, including holding and lifting a cup of coffee, and expert skills, such as an Olympic wrestler's holding and throwing an opponent. A fundamental question in limb motor control is whether the brain manages these contrasting goals of posture and movement through a single, robust control process or whether each engages a specialized control process. We addressed this question by examining how individual neurons in the primary motor cortex of macaque monkeys represent mechanical loads during posture and movement tasks. Notably, approximately half of the neurons that expressed load-related activity did so exclusively during either posture only or movement only. Further, those neurons with load-related activity during both tasks randomly switched their magnitude of response between tasks. These random changes in load representation suggest specialized control processes, one for posture and one for movement.

Action Potentials↗

PubMed2001

Postural arm control following cervical spinal cord injury.

This study used estimates of dynamic endpoint stiffness to quantify postural arm stability following cervical spinal cord injury (SCI) and to investigate how this stability was affected by functional neuromuscular stimulation (FNS). Measurements were made in the horizontal plane passing through the glenohumeral joint on three SCI-impaired arms, which ranged in functional level from a weak C5 to a strong C6. Endpoint stiffness, which characterizes the relationship between externally imposed hand displacements and the resultant forces, was estimated during the application of planar, stochastic perturbations to each arm. These estimates were used in conjunction with voluntary endpoint force measurements to quantify stability and strength during voluntary contractions and during voluntary contractions in the presence of triceps FNS. The primary findings were: 1) the differences in the force generating capabilities of these arms were due primarily to differences in shoulder strength; 2) measurements of strength alone could not be used to predict arm stability; and 3) triceps FNS improved postural arm stability for all tested conditions. These results suggest strategies for improved control of FNS systems designed to restore arm function following cervical SCI and underscore the importance of examining the effects of FNS on both strength and stability.

Algorithms↗

PubMed1999

Performance in functional balance tests during menopausal hormone replacement: a double-blind placebo-controlled study.

BACKGROUND AND PURPOSE: Recent studies have indicated that oestrogens might have an effect on postural control. The purpose of this study was to investigate the short-term effect of hormone replacement therapy (HRT) on postural control in menopausal women and to analyse the correlation between sway velocity measures and results of functional balance tests. SUBJECTS: 100 menopausal women who were randomized to receive either HRT or placebo for three months were included in the study. METHOD: The balance function was measured with nine different static and dynamic functional balance tests. The sway velocities were measured on a computerized force platform. RESULTS: No significant differences were found between the two groups in the results of the functional balance tests after the three-month placebo-controlled period or in the changes over time. However, some significant improvements occurred within both groups over this three-month period. The correlations between different sway velocities and the results of the functional balance tests were all very low (r < 0.35). CONCLUSION: It can not be concluded that HRT had a positive effect on the performance in the functional balance tests, as some improvement occurred in both groups. The low correlations indicate that the sway velocity and functional balance tests measure different aspects of balance function.

Analysis of Variance↗

PubMed2001

The multiple tasks test. Strategies in Parkinson's disease.

The clinical balance tests presently used cannot predict falls in Parkinson's disease (PD), perhaps because they probe fairly isolated "components" of postural control. The Multiple Tasks Test (MTT) is a new balance test that simultaneously assesses multiple components of postural control. We investigated whether this MTT can detect postural abnormalities in PD patients. Fifty young controls (mean age 27.6 years), 20 elderly controls (mean age 62.5 years), and 20 PD patients (mean age 61.8 years, mean Hoehn and Yahr stage 2.2) participated. The MTT consisted of eight separate tasks of increasing complexity, which were executed sequentially. These tasks were composed of several motor components (standing up, walking, avoiding obstacles, touching the floor, turning around, and sitting down) and one cognitive component (answering serial questions). Four additional components included carrying an empty or loaded tray, wearing slippery shoes, and reduced illumination. All components within each task had to be performed simultaneously or directly sequentially. Errors were defined as Hesitations (slowed performance) or Blocks (complete cessation), which were scored separately for execution of the motor and cognitive components. Speed of performance was not stressed, but we did measure the time taken to complete all tasks. The complete MTT was performed by all subjects, except for a subgroup of seven patients and seven elderly controls who performed a shortened version, with only three of the eight sequential tasks (simple, intermediate, and most difficult). The number of subjects that produced Hesitations or Blocks for the motor components differed between the three groups [two-way repeated measures MANOVA, F(2.7) = 20.56; P < 0.001], patients making more errors than young and elderly controls. Furthermore, the number of subjects that made motor errors increased as the tasks became more complex [F(2.7) = 6.69; P < 0.001]. This increase differed across the three groups [significant interaction effect; F(2.7) = 3.31; P < 0.001] because particularly patients produced motor errors during the more complex tasks. In both control groups, 62% performed all eight consecutive tasks without errors in the motor components. In contrast, only 8% of the patients completed all tasks without motor errors (log rank test, P < 0.0001). This difference between patients and controls disappeared if the cognitive component was also scored, because more controls made cognitive errors during complex tasks than patients. Controls apparently gave priority to execution of the motor components, which they performed significantly faster than the patients. Both patients and controls made more errors during the shortened MTT, suggesting that learning effects (gain in performance through practice) influenced performance on the complete test. The MTT is a new balance test that clearly discriminates between healthy subjects and PD patients. Unlike controls, PD patients lend less priority to motor tasks over cognitive tasks. In addition, impaired motor learning may partially explain the higher error rate in PD. Future studies must determine if impaired MTT performance can predict actual falls in daily life.

Adult↗