1. Field of the Invention
The present invention relates generally to medical devices, and more particularly, to improving an interface between electrode contacts of an implantable medical device and the neurons of a recipient.
2. Related Art
Medical devices having one or more implantable components, generally referred to as implantable medical devices, have provided a wide range of therapeutic benefits to patients over recent decades. Implantable hearing prostheses that treat the hearing loss of a prosthesis recipient are one particular type of implantable medical devices that are widely used today.
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, individuals suffer from hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the cochlea, and thus the sensory hair cells therein, are impeded, for example, by damage to the ossicles. Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As a result, individuals suffering from conductive hearing loss typically receive an implantable hearing prosthesis, such as an acoustic hearing aid, middle ear implant, etc., that generates mechanical motion of the cochlea fluid.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. As such, those suffering from some forms of sensorineural hearing loss are thus unable to derive suitable benefit from hearing prostheses that generate mechanical motion of the cochlea fluid. As a result, implantable hearing prostheses that deliver electrical stimulation to nerve cells of the recipient's auditory system have been developed. As used herein, the recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion, and parts of the brain used to sense sounds. Electrically-stimulating hearing prostheses include, but are not limited to, auditory brain stimulators and cochlear prostheses (commonly referred to as cochlear prosthetic devices, cochlear implants, cochlear devices, and the like; simply “cochlear implants” herein.)
In a normal ear, auditory nerve fibers are connected to spiral ganglion cells, which in turn are connected to peripheral processes (also referred to as dendrites), which in turn are connected to hair cells inside the Organ of Corti in the cochlea. Oftentimes sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which transduce acoustic signals into nerve impulses that are detected by the peripheral processes. Further, the loss of hair cells also eventually results in the loss of peripheral processes.
Cochlear implants generally use an electrode assembly implanted in the cochlea to deliver electrical stimulation signals directly to the spiral ganglion cells thereby bypassing absent or defective hair cells. The electrode contacts of the stimulating assembly differentially activate spiral ganglion cells that normally encode differential pitches of sound.