Neural Coding and Electrode Arrays in the Auditory Brainstem Implant
The Auditory Brainstem Implant (ABI) is a sophisticated neuroprosthetic device designed for individuals with a non-functional or absent auditory nerve. Unlike a cochlear implant, which stimulates the spiral ganglion cells in the inner ear, the ABI bypasses the ear and the nerve entirely to provide direct electrical stimulation to the cochlear nucleus in the brainstem.
The system consists of an external processor that captures acoustic signals and converts them into digital "pulse trains." These signals are transmitted to an internal receiver-stimulator connected to a paddle-shaped array of platinum electrodes (typically 12 to 21 contacts). The technical challenge lies in the "Tonotopic Mapping" of the brainstem; because the cochlear nucleus is not as clearly organized by frequency as the cochlea, each electrode must be individually "mapped" to a perceived pitch during post-surgical tuning to restore a sense of sound.