The maturation of the central auditory conduction in preterm infants until three months post term. II. The auditory brainstem responses (ABRs).

Auditory evoked brainstem responses (ABRs) were recorded in 65 preterm infants (serially in 55 of them), divided into 5 groups, according to their gestational age (GA). The recording sessions were performed at 8 conceptional age levels (CA = GA + chronological age), of which the last two were about 40 and 52 weeks CA. The number of recording sessions varied from one to seven. A full set of ABR latency and amplitude parameters was analyzed including peaks I, II, IIN, III, V and IIc, IIINc and Vc as well as some interpeak latency differences (IPLDs), and the amplitude ratios. The detectability of the different components in the ABR tests at 70 dB reached 80-100% at about 32 weeks CA. The side of stimulation nor the state of vigilance influences the detectability. The degree of prematurity in the 5 GA groups did not influence the development of the parameters. Neither the side of stimulation nor generally the state of vigilance give rise to different parameter values. The thresholds show an age dependent decrease, which is also determined by central maturation. The differential development of the latency decrease of the ABR parameters with increasing conceptional age can be associated with morphological maturational processes and may add weight to the arguments in the delineation of the sources of the ABR. The ipsi- and contralateral central conduction V-II and Vc-IIc do not show latency differences at any CA level. The components IIc and Vc, however, lagged behind in absolute latency compared with II and V. It is concluded that the ABR is a powerful instrument for the study of the maturation of the human auditory pathway in the brainstem. In view of the variability, the detectability and the complex changes within the ABR during the preterm period, its application for clinical purposes during this period has a limited value.