Towards a Diagnosis of Cochlear Neuropathy with Envelope Following Responses.
Listeners with normal audiometric thresholds can still have suprathreshold deficits, for example, in the ability to discriminate sounds in complex acoustic scenes. One likely source of these deficits is cochlear neuropathy, a loss of auditory nerve (AN) fibers without hair cell damage, which can occur due to both aging and moderate acoustic overexposure. Since neuropathy can affect up to 50 % of AN fibers, its impact on suprathreshold hearing is likely profound, but progress is hindered by lack of a robust non-invasive test of neuropathy in humans. Reduction of suprathreshold auditory brainstem responses (ABRs) can be used to quantify neuropathy in inbred mice. However, ABR amplitudes are highly variable in humans, and thus more challenging to use. Since noise-induced neuropathy is selective for AN fibers with high thresholds, and because phase locking to temporal envelopes is particularly strong in these fibers, the envelope following response (EFR) might be a more robust measure. We compared EFRs to sinusoidally amplitude-modulated tones and ABRs to tone-pips in mice following a neuropathic noise exposure. EFR amplitude, EFR phase-locking value, and ABR amplitude were all reduced in noise-exposed mice. However, the changes in EFRs were more robust: the variance was smaller, thus inter-group differences were clearer. Optimum detection of neuropathy was achieved with high modulation frequencies and moderate levels. Analysis of group delays was used to confirm that the AN population was dominating the responses at these high modulation frequencies. Application of these principles in clinical testing can improve the differential diagnosis of sensorineural hearing loss.
Program in Speech and Hearing Bioscience and Technology, Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, 02139, USA. lshaheen@mit.edu.|Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA, 02114, USA. lshaheen@mit.edu.
Luke A
LA
Shaheen
Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA, 02114, USA. Michelle_Valero@meei.harvard.edu.|Department of Otology and Laryngology, Harvard Medical School, Boston, MA, 02115, USA. Michelle_Valero@meei.harvard.edu.
Michelle D
MD
Valero
Program in Speech and Hearing Bioscience and Technology, Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, 02139, USA. Charles_Liberman@meei.harvard.edu.|Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA, 02114, USA. Charles_Liberman@meei.harvard.edu.|Department of Otology and Laryngology, Harvard Medical School, Boston, MA, 02115, USA. Charles_Liberman@meei.harvard.edu.
M Charles
MC
Liberman
D000818:Animals; D001309:Auditory Threshold; D003056:Cochlear Nerve / Q000503:physiopathology*; D003939:Diagnostic Techniques, Otological; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D008297:Male; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D009622:Noise / Q000009:adverse effects*; D000160:Vestibulocochlear Nerve Diseases / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology
acoustic overexposure; auditory brainstem response; auditory nerve; auditory neuropathy; auditory steady-state response; envelope following response; hidden hearing loss