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 th eir auditory system through a cochlear implant. Design: As a measure o f cortical auditory function, auditory evolved responses (AERs) were r ecorded from normal-hearing children and adults as well as from childr en and adults fitted with a cochlear implant. Morphological and latenc y 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 becomi ng 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 th e implanted population. Other typical features of the AER, namely N-1 and P-2, are either delayed in developing or absent in the implanted c hildren. Conclusions: These preliminary findings suggest both similari ties and differences in cortical auditory maturation for normal-hearin g and implanted children. For implanted children, the 5 yr delay for m aturation of P-1 latency roughly corresponds to the average 4.5 yr int erval between the onset of deafness and the time of implantation. Thes e findings suggest that during the period of deafness. maturation of c ortical auditory function does not progress. However, some, if not all , maturational processes resume after stimulation is reintroduced.