Early-stage development of auditory center: an experimental study of auditory evoked electrophysiologic recordings from fetal and newborn guinea pigs.

Five guinea pig fetuses at 8 weeks' gestation (term is 9 weeks) were tested for auditory brain stem response (ABR) generated by earphones placed outside the maternal abdomen. The results obtained from these fetuses were compared with the ABRs in 10 term newborn guinea pigs on the 1st and 20th day after delivery. The ABRs indicated a decreasing peak latency over wave III with increasing age. The interpeak latency to wave III-V decreased markedly, with very little change in wave I-III. The results suggested rapid maturation of the upper brain stem and midbrain during late gestation and in newborns. They also exhibited an increasing peak latency of ABRs from both fetuses and newborns with decreasing stimulus intensity.