Effect of sleep stages on transiently evoked oto-acoustic emissions in infants

Transiently evoked oto-acoustic emissions (TEOAEs) are generated by active contractions of the outer hair cells (OHC) of the organ of Corti. TEOAE are inhibited by the medial efferent olivocochlear system which originates in the brainstem and innervates the OHC. TEOAEs are a rapid non-invasive objective method of auditory screening in infants. Because in infants sleep represents 75% of their time, it was of interest to determine whether sleep stages which are induced in the brainstem could concomitantly affect TEOAEs. Repeated TEOAE recordings during polygraphic recordings of sleep stages were made on seven, 6-week-old infants. Results showed that: (i) TEOAE spectrum frequency components remained stable over sleep stages; (ii) TEOAE amplitude tended to increase during recording sessions; (iii) sleep stages (quiet, active and indeterminate sleep) did not affect TEOAE amplitude. This pilot study reveals that sleep mechanisms seem to have no effect on active OHC micromechanical properties. Therefore, in auditory screening, TEOAEs may serve to study active cochlear mechanisms in infants even during sleep which is the better time to perform recordings because of the quietness required.