Muscle-specific modulation of vestibular reflexes with increased locomotor velocity and cadence

Vestibular information is one of the many sensory signals used to stabilize the body during locomotion. When locomotor velocity increases, the influence of these signals appears to wane. It is unclear whether vestibular signals are globally attenuated with velocity or are influenced by factors such as whether a muscle is contributing to balance control. Here we investigate how vestibular sensory signals influence muscles of the leg during locomotion and what causes their attenuation with increasing locomotor velocity. We hypothesized that 1) vestibular signals influence the activity of all muscles engaged in the maintenance of medio-lateral stability during locomotion and 2) increases in both cadence and velocity would be associated with attenuation of these signals. We used a stochastic vestibular stimulus and recorded electromyographic signals from muscles of the ankle, knee, and hip. Participants walked using two cadences (52 and 78 steps/min) and two walking velocities (0.4 and 0.8 m/s). We observed phase-dependent modulation of vestibular influence over ongoing muscle activity in all recorded muscles. Within a stride, reversals of the muscle responses were observed in the biceps femoris, tibialis anterior, and rectus femoris. Vestibular-muscle coupling decreases with increases in both cadence and walking velocity. These results show that the observed vestibular suppression is muscle- and phase dependent. We suggest that the phase- and muscle-specific influence of vestibular signals on locomotor activity is organized according to each muscle's functional role in body stabilization during locomotion.

Cognitive-vestibular interactions: A review of patient difficulties and possible mechanisms

Cognitive deficits such as poor concentration and short-term memory loss are known by clinicians to occur frequently among patients with vestibular abnormalities. Although direct scientific study of such deficits has been limited, several types of investigations do lend weight to the existence of vestibular-cognitive effects. In this article we review a wide range of studies indicating a vestibular influence on the ability to perform certain cognitive functions. In addition to tests of vestibular patient abilities, these studies include dual-task studies of cognitive and balance functions, studies of vestibular contribution to spatial perception and memory, and works demonstrating a vestibular influence on oculomotor and motor coordination abilities that are involved in the performance of everyday cognitive tasks. A growing literature on the physiology of the vestibular system has demonstrated the existence of projections from the vestibular nuclei to the cerebral cortex. The goals of this review are to both raise awareness of the cognitive effects of vestibular disease and to focus scientific attention on aspects of cognitive-vestibular interactions indicated by a wide range of results in the literature.

Labyrinthectomy decreases bone mineral density in the femoral metaphysis in rats

To determine whether the vestibular system could influence bone remodeling in rats, we measured bone mineral density with dual energy X-rays absorptiometry before and 30 days after bilateral labyrinthectomy. Comparatively to intact control rats, labyrinthectomized animals showed a reduced bone mineral density in distal femoral metaphysis (p = 0.007): the variations between D0 and D30 were +3.0% for controls and -13.9% for labyrinthectomized rats. No significant difference between the 2 groups was observed in the whole body mineral density. These results suggest that the peripheral vestibular apparatus is a modulator of bone mass and more specifically in weight bearing bone. We discuss possible mechanisms of this vestibular influence probably mediated by the sympathetic nervous system.