Sensory strategies in human postural control before and after unilateral vestibular neurotomy

Abstract

Vestibular inputs tonically activate the anti-gravitative leg muscles during normal standing in humans, and visual information and proprioceptive inputs from the legs are very sensitive sensory loops for body sway control. This study investigated the postural control in a homogeneous population of 50 unilateral vestibular-deficient patients (Ménière's disease patients). It analyzed the postural deficits of the patients before and after surgical treatment (unilateral vestibular neurotomy) of their diseases and it focused on the visual contribution to the fine regulation of body sway. Static posturographic recordings on a stable force-plate were done with patients with eyes open (EO) and eyes closed (EC). Body sway and visual stabilization of posture were evaluated by computing sway area with and without vision and by calculating the percentage difference of sway between EC and EO conditions. Ménière's patients were examined when asymptomatic, 1 day before unilateral vestibular neurotomy, and during the time-course of recovery (1 week, 2 weeks, 1 month, 3 months, and 1 year). Data from the patients were compared with those recorded in 26 healthy, age- and sex-matched participants. Patients before neurotomy exhibited significantly greater sway area than controls with both EO (+52%) and EC (+93%). Healthy participants and Ménière's patients, however, displayed two different behaviors with EC. In both populations, 54% of the subjects significantly increased their body sway upon eye closure, whereas 46% exhibited no change or significantly swayed less without vision. This was statistically confirmed by the cluster analysis, which clearly split the controls and the patients into two well-identified subgroups, relying heavily on vision (visual strategy, V) or not (non-visual strategy, NV). The percentage difference of sway averaged +36.7%+/-10.9% and -6.2%+/-16.5% for the V and NV controls, respectively; +45.9%+/-16.8% and -4.2%+/-14.9% for the V and NV patients, respectively. These two distinct V and NV strategies seemed consistent over time in individual subjects. Body sway area was strongly increased in all patients with EO early after neurotomy (1 and 2 weeks) and regained preoperative values later on. In contrast, sway area as well as the percentage difference of sway were differently modified in the two subgroups of patients with EC during the early stage of recovery. The NV patients swayed more, whereas the V patients swayed less without vision. This surprising finding, indicating that patients switched strategies with respect to their preoperative behavior, was consistently observed in 45 out of the 50 Ménière's patients during the whole postoperative period, up to 1 year. We concluded that there is a differential weighting of visual inputs for the fine regulation of posture in both healthy participants and Ménière's patients before surgical treatment. This differential weighting was correlated neither with age or sex factors, nor with the clinical variables at our disposal in the patients. It can be accounted fo...

Walking performance of vestibular-defective patients before and after unilateral vestibular neurotomy

“…Compensatory mechanisms have very likely developed in Menière's patients before UVN, including increased functional weight of visual and proprioceptive cues. This hypothesis was already supported by posturographic recordings we performed in such pathology [27]. Adaptive plasticity in the control of locomotor trajectory has also been reported in normal subjects exposed to 2 h of walking on the perimeter of a horizontally rotating disc and asked thereafter to walk blindfolded straight ahead on firm ground [17].…”

“…In static posturographic recordings, the patients asked to stand quietly showed body sway modifications [27]. Circular locomotion tasks showed walking trajectory deviations pointing to vestibulospinal asymmetries [22].…”

Effect of visual surrounding motion on body sway in a three-dimensional environment

“…tently reported in the field of visual control of balance (Crémieux & Mesure, 1994;Isableu, Ohlmann, Cré-mieux, & Amblard, 1998;Lacour et al, 1997;Lestienne et al, 1977;Masson, Mestre, & Pailhous, 1995;Warren et al, 1996). For instance, Lestienne et al (1977) reported that 20% of subjects tested with linear motion of the visual scene did not show any postural readjustment.…”

Investigating the center of pressure velocity Romberg s quotient for assessing the visual role on the body sway

“…Considering RQ A as Gaussian distributed after excluding outliers and using a threshold based on the 95% confidence interval, Gagey and Weber (2005) only assumed as healthy those subjects with RQ A > 100. On the other hand, Chiari et al (2000), Da Silva et al (2006) and Lacour et al (1997) have found a bimodal RQ A distribution in healthy subjects.…”

“…Usually, the influence of visual input in the postural control has been studied using the classical Romberg's Quotient test (RQ) based on the elliptical sway area (RQ A ), defined as the ratio between the area values in EC and EO conditions (Chiari et al, 2000;Da Silva et al, 2006;Gagey and Weber, 2005;Lacour et al, 1997). Considering RQ A as Gaussian distributed after excluding outliers and using a threshold based on the 95% confidence interval, Gagey and Weber (2005) only assumed as healthy those subjects with RQ A > 100.…”