The maturation of the central auditory conduction in preterm infants until three months post term. I. Composite group averages of brainstem (ABR) and middle latency (MLR) auditory evoked responses.

Brainstem (ABR) and middle latency (MLR) auditory evoked responses were obtained sequentially in 49 preterm infants until three months post term date. In addition, the records of 16 preterm infants, obtained at different conceptional age levels, were included. The recording of these responses was performed successively in one procedure, together with auditory cortical evoked responses. The infants were divided into 5 groups according to their gestational age, i.e. the term at birth. Composite group averages were determined, showing the group stable components of the 5 gestational age groups at 8 different conceptional age levels, i.e. term at the time of the recording. The intra group stable components could thus be determined for further study of developmental trends in the responses. The group averages also serve as a reference in the visual analysis of the individual records. The averaged ABRs showed that with increasing conceptional age increasingly better identifiable waveforms were obtained. These were particularly outstanding for peaks I and V ipsilateral to stimulation, and peaks IIc and Vc contralateral to stimulation. This enabled the measurement of the central conduction times. The MLRs were especially remarkable for their latency changes which occurred in peak PO and the troughs Na and Nb. The results indicated that the conduction of the subcortical auditory afferent signals can be measured successfully in groups of very premature infants with ABRs and MLRs.