FUNCTIONAL MATURATION OF COCHLEAR ACTIVE MECHANISMS AND OF THE MEDIALOLIVOCOCHLEAR SYSTEM IN HUMANS

The aim of this study was to investigate the functional development of cochlear active mechanisms and of the medial efferent olivocochlear s ystem. Otoacoustic emissions (evoked and spontaneous) were recorded in 42 preterm neonates (conceptional age ranging form 33 to 39 weeks) an d a control group of 20 young normal-hearing adults. Medial olivochlea r system activity was examined by coupling evoked otoacoustic emission recording to a contralateral stimulation. Otoacoustic emission record ings were carried out using the Otodynamic ILO88 software and hardware . The stimuli were unfiltered clicks and the contralateral stimulation was broad band noise of 50 and 70 dBSPL delivered by an Adam generato r. The results revealed the presence of EOAEs and SOAEs from at least 33 weeks in humans, suggesting that the functional maturation of the o uter hair cells is nearly complete at that age. The study further reve aled that the contralateral stimulation had no effect on evoked otoaco ustic emissions in preterm neonates. The lack of activity observed in medial olivocochlear system indicated functional immaturity here, at l east before full-term birth.