The Hopkins study “is proof of concept that we can restore three-dimensional sensation of head movement with a multichannel vestibular prosthesis,” says Charles C. Della Santina, M.D., Ph.D., director of the Vestibular Neuroengineering Laboratory at Hopkins. In their report, the Hopkins team showed that a matchbox-size prototype device, weighing less than three ounces, effectively mimics the workings of the inner ear’s three semicircular canals by sensing head rotation and transmitting that information to the brain.

The device consists of a head-mounted, battery-operated box containing the sensors, which are positioned outside the head so that the sensors are parallel to the animal’s actual semicircular canals, where head rotation is normally sensed. The sensors are connected to a microprocessor and up to eight electrodes surgically implanted in the inner ear and separately connected to nerve endings. Each electrode can act as one information channel. In the chinchilla tests, pulses lasting less than a millisecond were delivered with timing patterns that mimicked normal nerve activity.

Santina and his colleagues first caused imbalance in chinchillas by treating them with a high dose of gentamicin, an antibiotic known to wipe out the tiny hairlike projections on cells in the inner ear canals that are normally key to sensory balance function. Treated animals displayed unsteady walking and wobbly eye movements commonly seen in people with impaired balance. Precise measurements of eye movements, using a technique of video-tracking adapted by researchers, were made during a fixed set of head movements. Results confirmed profound loss of normal eye-stabilizing reflexes.

The animals were then fitted with the vestibular prosthesis, with sensors oriented parallel to the semicircular canals they replaced. Post-activation eye testing showed, in three chinchillas mentioned in the report, that animals partially regained their vision-stabilizing reflex.; Source: Johns Hopkins Medical Institutions