Maturation of human cortical auditory function: Differences between normal-hearing children and children with cochlear implants

Objective: We investigated maturation of cortical auditory function in normal-hearing children and in children who receive stimulation of their auditory system through a cochlear implant. Design: As a measure of cortical auditory function, auditory evolved responses (AERs) were recorded from normal-hearing children and adults as well as from children and adults fitted with a cochlear implant. Morphological and latency changes for evoked responses recorded at electrode Cz are reported. Results: For normal-hearing children, there is a gradual evolution of AER features that extends through adolescence, with P-1 latency becoming adult-like in the late teens. Latency changes for P-1 occur at the same rate for implanted children, but the overall maturation sequence is delayed. By extrapolation from the existing data, the age at which P-1 latency becomes adult-like is delayed by approximately 5 yr for the implanted population. Other typical features of the AER, namely N-1 and P-2, are either delayed in developing or absent in the implanted children. Conclusions: These preliminary findings suggest both similarities and differences in cortical auditory maturation for normal-hearing and implanted children. For implanted children, the 5 yr delay for maturation of P-1 latency roughly corresponds to the average 4.5 yr interval between the onset of deafness and the time of implantation. These findings suggest that during the period of deafness. maturation of cortical auditory function does not progress. However, some, if not all, maturational processes resume after stimulation is reintroduced.