Maturation of auditory evoked potentials in young guinea pigs with binaural conductive hearing loss.

A reversible conductive hearing loss produced during the first 4 weeks post partum caused marked alterations in the development of click-evoked auditory brainstem (ABR) and middle latency (MLR) responses in guinea pigs. The early component PI in the ABR in controls showed adult-like latencies at the time of birth, while the later ABR components PIII and PV and all components investigated in the MLR showed postnatal development characterized by a shortened latency that persisted for the whole period of investigation. The course of the ABR latencies showed the sharpest decrease during the first 2-3 weeks of life, while that for the MLR took place during the first 5 weeks. In addition to the increased ABR thresholds and lengthened ABR latencies due to the conductive hearing loss, development of the ABR inter-peak latencies (IPL) and MLR latencies was retarded. The IPL reached control values 1 week after the end of the deprivation phase, while the delay in MLR started later (4th week) and lasted longer than did that in the ABR. These findings showed that a long-lasting postnatal conductive hearing loss does not generate sustained impairment at the level of the brainstem but can evoke longer-lasting deficiencies at higher stations of the auditory pathway.