Tissue resistivities determine the current flow in the cochlea.
OBJECTIVE
In individuals with severe to profound hearing loss, cochlear implants bypass normal inner ear function by applying electrical current directly into the cochlea, thereby stimulating cochlear nerve fibers. Stimulating discrete populations of spiral ganglion cells in cochlear implant users' ears is similar to the encoding of small acoustic frequency bands in a normal-hearing person's ear. Thus, spiral ganglion cells stimulated by an electrode convey the information contained by a small acoustic frequency band. Problems that refer to the current spread and subsequent nonselective stimulation of spiral ganglion cells in the cochlea are reviewed.


RESULTS
Cochlear anatomy and tissue properties determine the current path in the cochlea. Current spreads largely via scala tympani and across turns. While most of the current leaves the cochlea via the modiolus, the facial canal and the round window constitute additional natural escape paths for the current from the cochlea. Moreover, degenerative processes change tissue resistivities and thus may affect current spread in the cochlea.


CONCLUSIONS
Electrode design and coding strategies may result in more spatial stimulation of spiral ganglion cells, resulting in a better performance of the electrode-tissue interface.
Micco
Alan Gerard
AG
Northwestern University Feinberg School of Medicine, Department of Otolaryngology-Head and Neck Surgery, The Hugh Knowles Center, Chicago, Illinois , USA. agm109@northwestern.edu
Richter
Claus-Peter
CP
D003051:Cochlea / Q000502:physiology*; D003054:Cochlear Implants; D017097:Electric Impedance; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D006309:Hearing / Q000502:physiology*; D034381:Hearing Loss / Q000534:rehabilitation; D006801:Humans