Conclusion

This study demonstrates that the cortical tonotopic organization is altered by total deafness and that the central auditory pathway in adults remains capable of undergoing functional reorganization following reactivation of the auditory nerve via a cochlear implant. The similar temporal dynamics of the behavioural and electrophysiological responses indicate that when the sound information is adequately processed in the auditory cortex, it may result in proper perception of pitch and speech. This secondary plasticity seemed to be facilitated when the duration of deafness had been shorter and when the subject had worn a prosthesis before implantation or was using a contralateral prosthesis during the auditory rehabilitation by the implant. Age at implantation and auditory experience, before and after implantation, thus play a central role in laying down the fine organizational structure of the auditory pathway. It would be interesting to further investigate this plasticity of rehabilitation by studying the effects of auditory training on cortical tonotopy and implant benefit in humans as such training has been shown to modify the tonotopic cortical maps in animals (Recanzone et al., 1993; Bakin & Weinberger 1990; Edeline et al., 1993).