Auditory cortical responses in patients with cochlear implants

Currently the electrophysiological tests mostly used for cochlear implant evaluations are AEV, EABR and NRT. In this paper the Authors focus their interest on the study of the acoustic auditory cortical responses, or slow vertex responses (SVRs), that generally do not find large application due to the difficulty in recording especially in young children. The goals of this study consist in the verification of SVRs value and possible applications, in particular in monitoring the postimplant results considering the effective hearing restoration and auditory maturation. In practice, the use of tone-bursts even through the hearing aids as in SVRs, allows to evaluate much more frequencies and louder intensities than the other tests with a click as stimulus. Study design: Latencies of N1 and P2 SVR peaks were studied in cochlear implantees. Materials & Methods: Forty five implant recipients (aged 2 to 70 yr) were divided into five different homogeneous groups according to their chronological age, the age at the onset of deafness, and the age at implantation. For each subject, SVRs and free field auditory responses (PTAs) were recorded for tone-bursts at 500 and 2000 Hz before cochlear implant surgery (using hearing aid amplification) and during scheduled sessions at the 3rd and 12th month after implant activation. Results: N1 and P2 latencies decreased for all groups from the 3rd to the 12th mo after activation. Subjects implanted before school age or at least before age 8 yr exhibited the greatest latency change. For all subjects, a reduction of the gap between subjective thresholds (obtained with PTA) and objective thresholds (obtained with SVRs) measured with cochlear implant in comparison to those obtained in the presurgery stage with hearing aids was observed. Conclusions: A natural activation of the auditory pathway along the time especially in young children with prelingual deafness and implanted in preschool age was found. In any case cochlear implant seems to provide a real hearing restoration that is demonstrated by the sharp reducing of the gap between PTA and SVRs threshold.