The device, which researchers started testing more than a year ago, 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 animals 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.
Della Santina says people disabled by loss of vestibular sensation often feel chronically off balance and lose the ability to keep the eyes steadily pointed at an object when they move their head, seeing the world like the wobbly image on a shaky handheld video camera.
According to Della Santina, an assistant professor of otolaryngology - head and neck surgery and biomedical engineering at The Johns Hopkins University School of Medicine, this is the first implantable device made with multiple sensors and channels of processing that can measure and encode head rotation in all directions.
Each of the three sensors, he notes, can measure the speed of head rotation about one of three axes, or directional planes.
Della Santina says that previous implants developed elsewhere were limited to one functioning sensor and electrode and one plane or axis of rotation, when in reality, we move in multiple directions.
Every measurement in the balance device is processed in the implanted central microprocessor unit, using computer software developed by Della Santina and his team.
Once processed, the information is used to tailor timing of brief, electronic pulses through the electrodes implanted near the three branches of the vestibular nerve that respond to changes in head rotation. These branches normally carry signals from the inner ears three semicircular canals.