Cortical facilitation of somatosensory inputs using gravity-related tactile information in patients with bilateral vestibular loss
Résumé
A few years after their bilateral vestibular loss, individuals usually show a motor repertoire that
is almost back to normal. This recovery is thought to involve an up-regulation of the visual and
proprioceptive information that compensates for the lack of vestibular information. Here, we
investigated whether plantar tactile inputs, which provide body information relative to the
ground and to the Earth-vertical, contribute to this compensation. More specifically, we tested
the hypothesis that somatosensory cortex response to electric stimulation of the plantar sole in
standing adults will be greater in patients (n = 10) with bilateral vestibular loss than in an aged-
matched healthy group (n = 10). Showing significant greater somatosensory evoked potentials
(i.e., P1N1) in patients than in controls, the electroencephalographic recordings supported this
hypothesis. Furthermore, we found evidence that increasing the differential pressure between
both feet, by adding a 1 kg mass at each pending wrist, enhanced the internal representation of
body orientation and motion relative to a gravitational reference frame. The large decreased in
alpha/beta power in the right posterior parietal cortex (and not in the left) is in line with this
assumption. Finally, our behavioral analyses showed smaller body sway oscillations for
patients, likely originated from a tactile-based control strategy. Conversely, healthy subjects
showed smaller head oscillations suggesting a vestibular-based control strategy, the head
serving as a reference for balance control.
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