How ‘hidden hearing loss’ noise exposure affects neural coding in the inferior colliculus of rats

• Published in: Hearing research Vol. 443; p. 108963
• Main Authors: Bakay, Warren M.H., Cervantes, Blanca, Lao-Rodríguez, Ana B., Johannesen, Peter T., Lopez-Poveda, Enrique A., Furness, David N., Malmierca, Manuel S.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-03-2024
• Subjects: Cochlear synaptopathy; Hearing loss; Inferior colliculus; Noise exposure; Single unit electrophysiology; Temporary threshold shift; CF; BF; Inferior colliculus; Single unit electrophysiology; HHL; PTS; Hearing loss; ABR; TTS; Cochlear synaptopathy; FRA; RF; ANOVA; Temporary threshold shift; BWn; ANF; Noise exposure; IC; SEM; Qn
• ISSN: 0378-5955; 1878-5891; 1878-5891
• DOI: 10.1016/j.heares.2024.108963

•Noise exposure levels that induce PTS in other rodents only induce TTS in rats.•Rats develop cochlear synaptopathy and show similar electrophysiological changes to other rodents after noise exposure.•Short duration stimuli suggest a reduced number of fibres available to encode the auditory scene after noise exposure.
Exposure to brief, intense sound can produce profound changes in the auditory system, from the internal structure of inner hair cells to reduced synaptic connections between the auditory nerves and the inner hair cells. Moreover, noisy environments can also lead to alterations in the auditory nerve or to processing changes in the auditory midbrain, all without affecting hearing thresholds. This so-called hidden hearing loss (HHL) has been shown in tinnitus patients and has been posited to account for hearing difficulties in noisy environments. However, much of the neuronal research thus far has investigated how HHL affects the response characteristics of individual fibres in the auditory nerve, as opposed to higher stations in the auditory pathway. Human models show that the auditory nerve encodes sound stochastically. Therefore, a sufficient reduction in nerve fibres could result in lowering the sampling of the acoustic scene below the minimum rate necessary to fully encode the scene, thus reducing the efficacy of sound encoding.
Here, we examine how HHL affects the responses to frequency and intensity of neurons in the inferior colliculus of rats, and the duration and firing rate of those responses. Finally, we examined how shorter stimuli are encoded less effectively by the auditory midbrain than longer stimuli, and how this could lead to a clinical test for HHL.