  We investigated the effects of a plantar pressure-based tongue-placed
electrotactile biofeedback on postural control during quiet standing under
normal and altered vestibular and neck proprioceptive conditions. To achieve
this goal, fourteen young healthy adults were asked to stand upright as
immobile as possible with their eyes closed in two Neutral and Extended head
postures and two conditions of No-biofeedback and Biofeedback. The underlying
principle of the biofeedback consisted of providing supplementary information
related to foot sole pressure distribution through a wireless embedded
tongue-placed tactile output device. Centre of foot pressure (CoP)
displacements were recorded using a plantar pressure data acquisition system.
Results showed that (1) the Extended head posture yielded increased CoP
displacements relative to the Neutral head posture in the No-biofeedback
condition, with a greater effect along the anteroposterior than mediolateral
axis, whereas (2) no significant difference between the two Neutral and
Extended head postures was observed in the Biofeedback condition. The present
findings suggested that the availability of the plantar pressure-based
tongue-placed electrotactile biofeedback allowed the subjects to suppress the
destabilizing effect induced by the disruption of vestibular and neck
proprioceptive inputs associated with the head extended posture. These results
are discussed according to the sensory re-weighting hypothesis, whereby the
central nervous system would dynamically and selectively adjust the relative
contributions of sensory inputs (i.e., the sensory weights) to maintain upright
stance depending on the sensory contexts and the neuromuscular constraints
acting on the subject.
