Toward a Differential Diagnosis of Hidden Hearing Loss in Humans.
Recent work suggests that hair cells are not the most vulnerable elements in the inner ear; rather, it is the synapses between hair cells and cochlear nerve terminals that degenerate first in the aging or noise-exposed ear. This primary neural degeneration does not affect hearing thresholds, but likely contributes to problems understanding speech in difficult listening environments, and may be important in the generation of tinnitus and/or hyperacusis. To look for signs of cochlear synaptopathy in humans, we recruited college students and divided them into low-risk and high-risk groups based on self-report of noise exposure and use of hearing protection. Cochlear function was assessed by otoacoustic emissions and click-evoked electrocochleography; hearing was assessed by behavioral audiometry and word recognition with or without noise or time compression and reverberation. Both groups had normal thresholds at standard audiometric frequencies, however, the high-risk group showed significant threshold elevation at high frequencies (10-16 kHz), consistent with early stages of noise damage. Electrocochleography showed a significant difference in the ratio between the waveform peaks generated by hair cells (Summating Potential; SP) vs. cochlear neurons (Action Potential; AP), i.e. the SP/AP ratio, consistent with selective neural loss. The high-risk group also showed significantly poorer performance on word recognition in noise or with time compression and reverberation, and reported heightened reactions to sound consistent with hyperacusis. These results suggest that the SP/AP ratio may be useful in the diagnosis of "hidden hearing loss" and that, as suggested by animal models, the noise-induced loss of cochlear nerve synapses leads to deficits in hearing abilities in difficult listening situations, despite the presence of normal thresholds at standard audiometric frequencies.
Department of Otology and Laryngology, Harvard Medical School, Boston, MA, United States of America.|Eaton-Peabody Laboratory, Massachusetts Eye & Ear Infirmary, Boston, MA, United States of America.|Harvard Program in Speech and Hearing Bioscience and Technology, Boston, MA, United States of America.
M Charles
MC
Liberman
Department of Communication Sciences and Disorders, Bouvé College of Health Sciences, Northeastern University, Boston, MA, United States of America.
Michael J
MJ
Epstein
Department of Communication Sciences and Disorders, Bouvé College of Health Sciences, Northeastern University, Boston, MA, United States of America.
Sandra S
SS
Cleveland
Eaton-Peabody Laboratory, Massachusetts Eye & Ear Infirmary, Boston, MA, United States of America.
Haobing
H
Wang
Department of Otology and Laryngology, Harvard Medical School, Boston, MA, United States of America.|Eaton-Peabody Laboratory, Massachusetts Eye & Ear Infirmary, Boston, MA, United States of America.|Harvard Program in Speech and Hearing Bioscience and Technology, Boston, MA, United States of America.
Stéphane F
http://orcid.org/0000-0003-2813-6439
SF
Maison
D000293:Adolescent; D000328:Adult; D001299:Audiometry; D003937:Diagnosis, Differential; D034381:Hearing Loss / Q000175:diagnosis*; D006801:Humans; D055815:Young Adult