We hypothesized that cochlear frequency discrimination occurs through medial olivocochlear efferent (MOCE)-induced alterations in outer hair cell (OHC) electromotility, which is independent from basilar membrane traveling waves. After obtaining informed consent, volunteers with normal hearing (n = 10; mean age: 20.6 ± 1.2 years) and patients with unilateral deafness (n = 10; mean age: 30.2 ± 17.9 years) or bilateral deafness (n = 8; mean age: 30.7 ± 13.8 years) underwent a complete physical and audiological examination, and audiological tests including transient evoked otoacoustic emission and spontaneous otoacoustic emission (TEOAE and SOAE, respectively). SOAE recordings were performed during contralateral pure-tone stimuli at 1 and 3 kHz. SOAE recordings in the presence of contralateral pure-tone stimuli showed frequency-specific activation out of the initial frequency range of SOAE responses. Basilar membrane motion during pure-tone stimulation results from OHC activation by means of MOCE neurons rather than from a traveling wave. Eventually, frequency-specific responses obtained from SOAEs suggested that OHC electromotility may be responsible for frequency discrimination of the cochlea independently from basilar membrane motion.
The medial olivocochlear efferent (MOCE) branch synapses with outer hair cells (OHCs), and the efferent pathway can be activated via a contralateral acoustic stimulus (CAS). The activation of MOCE can change OHC motile responses and convert signals that are capable of controlling the sensitivity of the peripheral hearing system in a frequency-specific manner. The aim of this study was to examine the MOCE system activity in professional musicians using transient evoked otoacoustic emission test and CAS. Musician group showed stronger suppression in all frequency bands in the presence of CAS.