Sensorineural hearing loss initiates a cascade of anatomical and functional changes within the auditory system. The secondary loss of spiral ganglion neurones, the target cells of cochlear implants, is the most critical peripheral change; and there are a range of atrophic changes within the central auditory pathway. However, equally important are the functional changes, particularly the degradation in spatial (spectral) and temporal processing, that occur within the central auditory system. Over the past decade, we have focussed on the changes in the response of the primary auditory cortex in the cat to intracochlear electrical stimulation with long-term, ototoxically induced, profound deafness. The most striking effect is a complete loss of the normal cochleotopic organisation seen in normal hearing animals. We have also examined the effects of chronic environmentally derived intracochlear electrical stimulation, delivered by a cochlear implant, on central auditory processing. Specifically, chronic cochlear implant use can drive the cochleotopic organisation of primary auditory cortex, both in young and mature animals. The effects of cochlear implant use can be observed after as little as one month of chronic use, highlighting the importance of early (re)habilitation following implant activation in a clinical setting. The excellent performance of cochlear implant recipients has also led to a relaxation of the criteria for candidacy for implantation. Initially only implanted in patients with no useful hearing in either ear, patients with significant amounts of low-frequency hearing are now routinely implanted, who previously would only have been treated with hearing aids. These patients have access to information from both acoustic hearing (via their remaining low-frequency hearing) and electric hearing (via their cochlear implant stimulating the more basal, high frequency region of the cochlea). However, it is unclear how the central auditory system represents and integrates the two modalities of stimulation. Therefore, we have begun examining the representation of both acoustic and electric activation of the cochlea in ototoxically partially deafened animals, some of whom have received a cochlear implant.