ISSN 1308-7649 | E-ISSN 2148-3817
Original Article
A New Hypothesis on the Frequency Discrimination of the Cochlea
1 Department of Audiology, Trakya University Faculty of Health Sciences, Edirne, Turkey; Department of Physiology, Trakya University School of Medicine, Edirne, Turkey  
2 Department of Otorhinolaryngology, Trakya University School of Medicine, Edirne, Turkey  
3 Department of Physiology, Trakya University School of Medicine, Edirne, Turkey.  
4 Center of In-vitro Fertilization, Marmara University School of Medicine, İstanbul, Turkey  
5 Department of Histology and Embryology, İstanbul Medeniyet University School of Medicine, İstanbul, Turkey  
6 Department of Histology and Embryology, Acıbadem University School of Medicine, İstanbul, Turkey  
J Int Adv Otol ; : -
DOI: 10.5152/iao.2017.2027
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Key Words: Efferent pathways, cochlear outer hair cells, otoacoustic emissions, spontaneous, basilar membrane, microscopy, electron, scanning
Abstract

OBJECTIVE: Medial olivocochlear efferent (MOCE) neurons innervate outer hair cells (OHCs) of the cochlea, which in turn leads to basilar membrane motion. We hypothesized that MOCE-induced alterations in basilar membrane motion, independent of traveling waves, is responsible for the cochlear frequency discrimination of sound.

 

MATERIALS and METHODS: Eleven guinea pigs underwent bilateral otoscopic and audiologic evaluations under general anesthesia. The study comprised two parts. Part I (n=11) included spontaneous otoacoustic emission (SOAE) recordings with or without contralateral pure-tone acoustic stimuli (1 and 8 kHz) at 60 dB sound pressure level (SPL). Part II involved pure-tone (1 or 8 kHz) acoustic trauma in the right ears of two randomly selected subgroups (G1: 1 kHz; n=4 and G8: 8 kHz; n=4). The remaining three animals served as controls. After frequency-specific deafness was confirmed by distortion product otoacoustic emission (DPOAE), SOAEs were recorded in the left ears in the presence of a contralateral pure-tone (1 and 8 kHz) stimulus of 60 dB SPL. Furthermore, the surface of the organ of Corti was examined by scanning electron microscopy (SEM).

 

RESULTS: The contralateral pure tone led to frequency-specific activation in SOAEs in part I (without trauma) and part II (with trauma) measurements. SEM showed heterogeneous OHC damage along the cochlea in traumatized ears with pure tone.

 

 

CONCLUSION: We suggest that MOCEs convey acoustic information from traumatized ears to intact ears. Traumatized ears can show frequency-specific activation in the presence of diffuse damage in OHCs that excludes the passive transmission of the pressure wave from the perilymph to the basilar membrane.

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