Vestibular loss induces a combination of postural, oculomotor, and perceptive symptoms that are compensated over time. The aim of this study was to analyze the influence of betahistine dihydrochloride on vestibular compensation. A randomized, double-blind, placebo-controlled study was performed in Menière's disease patients who underwent a curative unilateral vestibular neurotomy (UVN). The effects of betahistine treatment were investigated on a broad spectrum of vestibular-induced changes resulting from vestibular loss: body sway, head orientation, ocular cyclotorsion, spontaneous nystagmus, verticality perception, and self-evaluation of the postural stability. The time course of the recovery was compared in 16 patients who received either a placebo or betahistine (24 mg b.i.d.) from 3 days up to 3 months after UVN. Patients were examined before (day -1) and after UVN (days 7, 30, and 90). Results indicate that betahistine reduces the time to recovery by 1 month or more depending on the tested functions. Betahistine was effective as soon as 4 days after treatment administration, and the effect remained during the whole compensation period (up to 3 months). The observed clinical effects may be attributed to an action of betahistine in rebalancing the neuronal activity between contralateral vestibular nuclei.
Any action performed by standing subjects is generally accompanied by compensatory postural activities, which reduce or abolish the postural disturbance generated by the movements and keep the subjects' center of gravity within the supporting base. These postural activities are triggered by either anticipatory and/or feedback-based control processes, depending on the information available and on the behavioral context. To investigate the respective involvement of these two components in postural control during development, we studied the extent to which the postural equilibrium of children (3-to 10-year-olds) and adults was disturbed by the same physical event, an unloading, depending on whether it was initiated by the subject or externally imposed. The subjects were standing on a force platform with their eyes closed, holding a load (5% of their own body weight) in their hands, with arms vertical and forearms horizontal. Two conditions were applied: (1) the subjects voluntarily released the load and (2) the load was unpredictably removed. The unloading resulted in a backward movement of the center of pressure, which was smaller with self-initiated than imposed disturbances in all age groups. This difference varied depending mainly on the age-related changes in the relative amplitude of the self-initiated disturbance, which decreased between 3- to 5-, and 6- to 8-year-olds (who showed no marked postural instability after self-initiated unloading), and increased again in the two older groups (9- to 10-year-olds and adults), in which it also became more consistent It was concluded that feedforward control. becomes more efficient as children grow up, but that its relative contribution to postural control does not show a monotonic pattern of development.
We studied the development of the coordination between posture and movement by analyzing the shifts of the center of pressure (CoP) associated with arm raising. Three groups of children aged 3-5 years, 6-8 years, and 9-10 years and an adult group were tested. The subjects were required to raise their arms to the horizontal position while standing still, with their hands free or loaded (5% of the body weight). The arm movements were recorded by a TV-image processor, and the changes in position of the CoP were measured by a force platform and analyzed before, during, and after the arm movement. The data show that the CoP moved forward during arm raising, that additional load induced a greater shift in all age groups, and that the relative amplitude of the shift decreased with age. The greatest changes occurred between ages 3-5 years and 6-8 years. The pre- and postmovement CoP shift suggests qualitative changes in the postural adaptation to movement between these two age groups: the anticipatory postural adjustments moved from a supporting function to a compensatory function, yielding an increasing functional convergence between the feedforward and the feedback modes of postural control, and an increasing rapidness in recovering postural stability after arm movement. The postural behavior shown by the 9- to 10-year-old children and by the adults in the arms-free condition suggests an increased tolerance to unbalance when postural oscillations do not jeopardize static equilibrium.
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