Vestibular prosthesis

The vestibular system, the inner-ear partner of the cochlea, senses head rotation (three semicircular canals) and linear acceleration and gravity (the otoliths); its bilateral loss causes disabling oscillopsia (the world bouncing with every head movement) and chronic imbalance for which there is no good treatment. A vestibular prosthesis senses head motion with gyroscopes and accelerometers and encodes it as modulation of the baseline firing rate of the corresponding ampullary (semicircular-canal) nerve branches — increasing rate for excitatory head turns, decreasing it for the opposite direction — to restore the vestibulo-ocular reflex (VOR) that stabilizes gaze.

Human feasibility has been demonstrated: multichannel canal implants (some adapting cochlear-implant hardware) partially restore the VOR, improve posture and gait, and reduce oscillopsia over months of adaptation. Key challenges are shared with the cochlea and then some — current spread makes the three canals interact (misaligned, cross-axis eye responses), chronic stimulation and electrode insertion can damage residual vestibular and even cochlear function, and the system must encode a bidirectional, sensor-driven signal continuously. Otolith (linear) restoration is far less developed than canal (rotational) restoration.