Abstract

A tonotopic organization of the auditory cortex was evidenced in cochlear implant users with at least three months of implant use (Guiraud et al., submitted). However, it is not known whether experienced implant recipients use pre-existing cortical maps or whether the use of the implant leads to a reorganization of the auditory cortex. Indeed, it is not certain that deafness had altered the original tonotopic organization prior to implantation. Two aspects needed then to be further investigated. Firstly, does total deafness alter the tonotopic organization of the auditory cortex? Secondly, what are the plastic changes of this organization within the first times of cochlear implant use? The present study consisted then to follow up over one month the functional changes of the auditory cortex in five subjects from implant switch on. Auditory event-related potentials were recorded in response to current pulses delivered at different implant electrodes. Individual topographic analysis of the auditory N1 component within the first two days of implant use showed no ordered organization as a function of stimulation site in the cochlea. After one month of cochlear implant use, the potential maps in four subjects showed modifications in the positive/negative extremum locations on the scalp according to the stimulated electrode. This frequency-dependent organization was similar to the one found in experienced implantees and normal-hearing subjects. The present study therefore showed that total deafness leads to a reorganization of the cortical tonotopic maps that is reversible in most subjects with cochlear implantation. Investigation of the subjects’ ability to scale pitch at both sessions showed that improvement in the perception of pitch paralleled the cortical reorganization shown in N1 topographies. These plastic changes in the auditory cortex have thus important implications for implants benefit since pitch and speech perception are related.

Keywords: Cortical tonotopy, Cochlear implant, Electroencephalography, Pitch perception, Plasticity