Auditory brain stem and midbrain development after cochlear implantation in children

Input to the central auditory system through a cochlear implant promotes psychophysical improvement of auditory skills. However, the developmental changes along the pathways have never been characterized in children with hearing loss who use implants. We aimed to measure auditory development in such children by using the electrically evoked auditory brain stem response (EABR). We made repeated measures of the EABR in 41 nonsedated children with implants before chronic stimulation and after 2, 6, and 12 months of consistent implant use. The results show that EABRs were present in all of the children even before chronic auditory stimulation, and that EABR wave latencies decreased from the time of initial activation throughout the first year of cochlear implant use. These findings reflect auditory development to the level of the midbrain as a result of the cochlear implant. The decreasing latencies likely reflect decreased neural conduction times at this level, in part because of increased synaptic efficacy.