Histopathology of an ear after 5 years of electrical stimulation.

Four electrodes were placed in the cochlea and eighth nerve of a 57-year-old man, deafened earlier by neomycin. One electrode received over 4,000 known hours of electrical stimulation and the others fewer, but still substantial hours during extensive psychometric and speech-related testing. While tissue examination showed nerve damage in the basal turn secondary to the implant surgery, there were 18,450 surviving neurons (25,000 are normal for age). There was little or no local tissue reaction and no erosion of the electrode tips caused by electrical stimulation.