The microscopic examination of fifty-five serially sectioned implanted temporal bones has provided insight into what is being stimulated; and the changes that are the result of the insertion and presence of the implant. The ganglion cell bodies (neurons) are structures being stimulated (two laboratories have reported an inverse relationship of the number of neurons and performance). Insertion through the round window, verses a cochleostomy, produces the least fibrosis and new bone. Fibrosis and new bone do not affect the implant function unless they form in the scala vestibuli in the region of the ductus reuniens, and, block it; and produce cochlear hydrops resulting in a delayed low tone loss of hearing in hybrid implants. Animal models cannot be applied to humans because of the difference in size and myelination of the neurons.
Keywords: Cochlear implant.