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PubMed2003

Basal ganglia efferents to the brainstem centers controlling postural muscle tone and locomotion: a new concept for understanding motor disorders in basal ganglia dysfunction.

The present study is designed to elucidate how basal ganglia afferents from the substantia nigra pars reticulata (SNr) to the mesopontine tegmental area of the brainstem contribute to gait control and muscle-tone regulation. We used unanesthetized and acutely decerebrated cats (n=27) in which the striatum, thalamus and cerebral cortex were removed but the SNr was preserved. Repetitive stimulation (50 Hz, 10-60 microA, for 5-20 s) applied to a mesencephalic locomotor region (MLR), which corresponded to the cuneiform nucleus, and adjacent areas, evoked locomotor movements. On the other hand, stimulation of a muscle-tone inhibitory region in the pedunculopontine tegmental nucleus (PPN) suppressed postural muscle tone. An injection of either glutamatergic agonists (N-methyl-D-aspartic acid and kainic acid) or GABA antagonists (bicuculline and picrotoxin) into the MLR and PPN also induced locomotion and muscle-tone suppression, respectively. Repetitive electrical stimuli (50-100 Hz, 20-60 microA for 5-20 s) delivered to the SNr alone did not alter muscular activity. However stimulating the lateral part of the SNr attenuated and blocked PPN-induced muscle-tone suppression. Moreover, weaker stimulation of the medial part of the SNr reduced the number of step cycles and disturbed the rhythmic alternation of limb movements of MLR-induced locomotion. The onset of locomotion was delayed as the stimulus intensity was increased. At a higher strength SNr stimulation abolished the locomotion. An injection of bicuculline into either the PPN or the MLR diminished the SNr effects noted above. These results suggest that locomotion and postural muscle tone are subject to modulation by GABAergic nigrotegmental projections which have a partial functional topography: a lateral and medial SNr, for regulation of postural muscle tone and locomotion, respectively. We conclude that disorders of the basal ganglia may include dysfunction of the nigrotegmental (basal ganglia-brainstem) systems, which consequently leads to the production of abnormal muscle tone and gait disturbance.

Animals↗
PubMed1995

Mefloquine Prophylaxis and Hearing, Postural Control, and Vestibular Functions.

Background: Mefloquine (MQ) is an important antimalarial drug. Dizziness and other adverse neuropsychiatric reactions have however restricted its use. Method: Ten healthy adult volunteers were given MQ (Lariam) 250 mg once weekly for 16 weeks. Measurement of postural sway (posturography), nystagmus recording, determinations of hearing thresholds (Bekesy audiometry), and determinations of drug concentrations were done before, after 4, 32, and 109 days of weekly MQ intake and 3 months after the last dose. Results: All volunteers were able to continue their professional work and normal daily activities. Several mild symptoms were reported. In at least one of the volunteers, these symptoms were probably caused by the MQ intake. Hearing thresholds remained normal. No significant changes were noted in the nystagmus tests. The recorded values of sway index were within the normal range (99% confidence interval) in all volunteers in all test situations, and no differences were seen at the time of maximal drug concentrations (day 109) compared to before or after the study. There was no correlation between the plasma concentrations of MQ, the two MQ enantiomers (RS and SR), or the main mefloquine metabolite and the sway index. Conclusion: Although no effect was seen on the vestibular system in the present study, further tests in a flight simulator will be needed before MQ can be recommended for pilots. (J Travel Med 2:66-69, 1995)

Journal Article↗
PubMed1979

Vagal and sinoaortic reflexes in postural control of circulation and renin release.

Anesthetized cats were subjected to two 10-min trials of head-up tilting spaced 60 min apart. Bilateral cervical vagotomy, performed after the first tilting episode, did not affect the hemodynamic response to the change in posture, but significantyly and markedly reduced the increase in renin release from the innervated kidney. After sinoaortic denervation a marked and sustained arterial hypotension occurred during tilting, and the postural increase in renin release, though still limited to the innervated kidney, was even greater. When pressure homeostasis to tilting was disturbed, the renin release response was seen to be independent of the vagi, as it occurred after combined vagotomy and sinoaortic denervation. Maintenance of arterial pressure during tilting is mainly due to sinoaortic reflexes, whereas vagal reflexes are mostly responsible for the postural increase in renin release. The vagally independent release of renin observed when the cardiovascular response to tilting is impaired, is probably due to a direct action of arterial hypotension on intrarenal receptors, an action occurring only in innervated kidneys.

Animals↗
PubMed2000

Intrasession reliability of the "center of pressure minus center of mass" variable of postural control in the healthy elderly.

OBJECTIVES: To estimate the intrasession reliability of a single measure of the biomechanical variable "center of pressure minus center of mass" (COP-COM) to determine, first, how many trials must be averaged to obtain a reliable measure of postural stability, and second, the minimal metrically detectable change of the COP-COM. PARTICIPANTS: Community-living, healthy, elderly people over 60 years of age (n = 7). DESIGN: Measurements were made in double leg stance, eyes-open condition. Nine successive trials, with rests between, were carried out for each subject. DATA ANALYSIS: Intraclass correlation coefficients (ICCs). MAIN OUTCOME MEASURE: The biomechanical variable COP-COM, which represents the distance between the center of pressure and the center of mass, was measured from two force platforms and three position sensors. RESULTS: The ICCs obtained for one measure of the COP-COM were .79 in the anterior-posterior (AP) direction and .69 in mediolateral (ML) direction. With four trials, the COP-COM variable is reliable at .94 in the AP direction and .90 in the ML direction. Minimal metrically detectable changes were .10 mm (AP) and .16 mm (ML). CONCLUSION: Using four repetitions of the COP-COM variable provides a reliable measurement of postural stability.

Aged↗
PubMed1997

Nature and nurture in the development of postural control in human infants.

Nowadays, the controversy on "nature" and "nurture" in motor development focuses on the development of automatic motor patterns. The present paper discusses this issue within the framework of a recent study on the effect of maturation and training on the development of postural adjustments in sitting infants. This study revealed that already before the age of sitting without help, highly variable but direction-specific muscle activation patterns are present. This suggests that postural adjustments develop via an innate repertoire of primary direction-specific response patterns. The following developmental step consists of a decrease in muscle activation patterns, which results in selection of the most complete patterns of synergist activation. In accordance with Edelman's neuronal group selection theory, pattern selection turned out to be experience dependent, as it appeared to be guided by cues on head stabilization and enhanced by daily balance training.

Child Development↗
PubMed1999

Preservation of postural control of transient lower oesophageal sphincter relaxations in patients with reflux oesophagitis.

INTRODUCTION: In normal subjects, transient lower oesophageal sphincter relaxations (TLOSRs) and gas reflux during belching are suppressed in the supine position. Supine reflux, however, is a feature of reflux disease. AIMS: To investigate whether postural suppression of TLOSRs and gas reflux is impaired in patients with reflux disease. PATIENTS: Ten patients with erosive oesophagitis. METHODS: Oesophageal manometry was performed during gastric distension with 750 ml carbon dioxide. Measurements were made for 10 minutes before and after distension in both sitting and supine positions. RESULTS: In the sitting position gastric distension substantially increased the rate of gas reflux (median (interquartile range)), as evidenced by increases in oesophageal common cavities from 1 (0-1)/10 min to 7 (5-10)/10 min and TLOSRs from 1 (1-1.5)/10 min to 6 (2.5-8)/10 min. However, this effect was suppressed in the supine position in all but one patient (TLOSRs 0 (0)/10 min to 1 (0-4.5)/10 min, common cavities 0 (0)/10 min to 0.5 (0-2)/10 min). CONCLUSIONS: Postural suppression of TLOSRs and gas reflux is generally preserved in reflux disease.

Adult↗
PubMed2005

The effect of cataract surgery on postural control.

PURPOSE: Falls are a significant cause of morbidity in the elderly. Because decreased vision is known to be a significant risk factor for falling in this age group, we sought to examine the effect of the removal of cataract, a major cause of visual handicap, on postural stability. METHODS: Postural stability was measured in 23 patients who underwent cataract surgery, before and 1 to 4 months after surgery. Stability indices included Stability Effect, Fourier Spectrum of Postural Sway, and Synchronizations, and, based on these measurements, Falling Index, which had been shown in earlier studies to predict the risk of falling. RESULTS: Visual acuity in the surgical eye significantly improved in all patients after surgery (P < 0.01) and did not change in the fellow eye. Stability improved in most patients (19/23) and Fourier Spectrum of Postural Sway improved in the high-frequency bands (above 0.5 Hz), when viewing with the surgical eye, but not when viewing with the nonsurgical eye (P < 0.05). By Falling Index, before surgery, 12 of 23 patients were at high risk of falling, and only six were at low risk. After surgery, 16 of 23 were at low risk and only three remained at high risk (chi(2) test, P < 0.008). CONCLUSIONS: Cataract surgery significantly improves postural stability. Considering the high cost of treating fall-related injuries in the elderly, the findings may imply that cataract surgery is cost effective in this regard.

Accidental Falls↗
PubMed2005

Evidence for reflex and perceptual vestibular contributions to postural control.

Vestibular signals are known to have an important role in stance under specific conditions. Potentially these effects could be modulated by vestibular reflexes or by voluntary responses to perceived vestibular signals. Our preliminary aim was to confirm that vestibulospinal reflexes change in parallel with sway under different postural conditions, and then to determine whether any relationship was present between these reflexes and body sway within fixed postural conditions. Sixteen subjects (eight male, eight female) were tested in conditions assessing the effects of vision (eyes open or closed), support surface (firm or compliant), external support (with or without) and stance width (feet apart or together). Sway (centre of pressure) in the anteroposterior (AP) and mediolateral planes was measured using a force platform. A subgroup of 11 subjects (five male, six female) underwent testing to measure short (SL) and medium latency (ML) reflexes from soleus. Bipolar, transmastoid galvanic stimulation (1 mA, 200 ms) was administered while subjects stood in the most unstable of our conditions (eyes closed, compliant surface and feet together). In the final part, to assess possible perceptual contributions to body sway, short duration AP sway levels were measured and expressed in angular terms (sway in mrad, velocity in mrad s(-1)) in the 11 subjects for both our baseline (eyes open, firm surface and feet apart) and most unstable conditions. Average sway levels increased more than seven-fold between conditions and had significant, positive correlations with reported changes in mean vestibulospinal reflexes under similar conditions (overall r = 0.75, P < 0.001). However, the SL reflex for the subgroup of 11 subjects had a significant negative correlation (r = -0.71; P = 0.014) with the degree of AP sway in the condition with maximum reliance on vestibular inputs (eyes closed, compliant surface, and feet together). Under baseline conditions, 5/125 (4%) of the short-term AP sway displacements were above the threshold previously reported for the detection of imposed sway. In the unstable condition, when sway was increased, 43/138 (31%) of the short-term AP sway movements were above the threshold for perception of imposed body sway based on vestibular signals. Our results confirm that vestibulospinal reflexes appear to be acutely facilitated as body sway increases. For the most unstable condition, when non-vestibular information was absent or attenuated, subjects with larger SL reflexes had less AP sway, suggesting that the SL reflex acted to attenuate sway. Under the same condition, short duration sway levels increased such that 31% were above the previously published threshold for detection using vestibular afferents. We conclude that both vestibular reflexes and perceptual signals appear to have a specific role in the maintenance of upright stance, under conditions in which other sources of postural information are attenuated or absent.

Adult↗
PubMed2001

Postural control as assessed with virtual reality.

We studied the use of virtual reality technology as a stimulus in balance examinations. A pilot study was made using a small group of healthy subjects to investigate the effect of alcohol and virtual reality stimulus on the subjects' balance. The tests showed that blood alcohol concentration accounted for almost 50% of the increased lateral body sway velocity. The new stimulus technique based on virtual reality technology seems to be effective and flexible for postural investigations.

Adult↗
PubMed1996

Motion parallax is used to control postural sway during walking.

Three experiments tested the hypothesis that postural sway during locomotion is visually regulated by motion parallax as well as optical expansion. Oscillating displays of three-dimensional scenes were presented to participants walking on a treadmill, while postural sway was recorded. Displays simulated: (a) a cloud, in which parallax and expansion are congruent, (b) a hallway, (c) the side walls of the hallway, (d) a ground surface, (e) a wall, (f) the wall with a central hole, (g) a hall farther from the observer, and (h) a wall farther from the observer. In contrast to previous results with a hallway, responses with the cloud were isotropic and directionally specific. The other displays demonstrated that motion parallax was more effective than simple horizontal flow in eliciting lateral sway. These results are consistent with the hypothesis that adaptive control of sway during walking is based on congruent expansion and parallax in natural environments.

Adult↗
PubMed2000

Postural control model interpretation of stabilogram diffusion analysis.

Collins and De Luca [Collins JJ. De Luca CJ (1993) Exp Brain Res 95: 308-318] introduced a new method known as stabilogram diffusion analysis that provides a quantitative statistical measure of the apparently random variations of center-of-pressure (COP) trajectories recorded during quiet upright stance in humans. This analysis generates a stabilogram diffusion function (SDF) that summarizes the mean square COP displacement as a function of the time interval between COP comparisons. SDFs have a characteristic two-part form that suggests the presence of two different control regimes: a short-term open-loop control behavior and a longer-term closed-loop behavior. This paper demonstrates that a very simple closed-loop control model of upright stance can generate realistic SDFs. The model consists of an inverted pendulum body with torque applied at the ankle joint. This torque includes a random disturbance torque and a control torque. The control torque is a function of the deviation (error signal) between the desired upright body position and the actual body position, and is generated in proportion to the error signal, the derivative of the error signal, and the integral of the error signal [i.e. a proportional, integral and derivative (PID) neural controller]. The control torque is applied with a time delay representing conduction, processing, and muscle activation delays. Variations in the PID parameters and the time delay generate variations in SDFs that mimic real experimental SDFs. This model analysis allows one to interpret experimentally observed changes in SDFs in terms of variations in neural controller and time delay parameters rather than in terms of open-loop versus closed-loop behavior.

Computer Simulation↗