Assessing Hidden Hearing Loss After Impulse Noise in a Mouse Model

Abstract

Introduction: There are several key differences between impulse and continuous noise: the nature of the noise itself, the cochlear and neuronal structures affected, the severity to which they damage the auditory system, and the period of time in which damage occurs. Notably, no work on hidden hearing loss after impulse noise exposure has been done to this point, though it has been extensively studied after continuous noise. Hidden hearing loss manifests physiologically with reductions in suprathreshold amplitudes of the first wave of the auditory brainstem response, while auditory thresholds can remain relatively normal.

Objective: This study aimed to assess the extent to which, if at all, hidden hearing loss is present after exposure to impulse noise in C57BL6/J mice.

Methods: Thirty-one C57BL6/J mice were used in the experiment, in accordance with IACUC protocols. Auditory brainstem responses were recorded before and after noise exposures. The noise exposures consisted of 500 impulses at 137 dB peSPL.

Results: Suprathreshold amplitude reductions in the P1 wave of the mouse auditory brainstem response were seen, but only at frequencies with significant threshold shift.

Conclusion: These amplitude changes were consistent with hidden hearing loss, and we conclude that impulse noise can cause hidden hearing loss, but future studies are required to determine the specific mechanisms involved and if they parallel those of hidden hearing loss after continuous noise.

Keywords: Auditory brainstem response; cochlea; hidden hearing loss; impulse noise; noise.

Figure 1

ABR thresholds for the mice before and after impulse noise exposure. Error bars represent ± 1 standard deviation. N = 31 for Pre, Day 3, and Day 7. N = 29 for Day 21. Significant differences between Pre and all other days as well as between Day 3 and Day 21 are shown with an asterisk (*). Significant differences only between Pre and all other days are shown with two asterisks (**).

Figure 2

ABR P1 wave amplitudes for the mice before and after impulse noise exposure. The top, center, and bottom panels represent 8, 16, and 24 kHz data, respectively. Error bars represent ±1 standard deviation. N = 31 for Pre, Day 3, and Day 7. N = 29 for Day 21. Levels at which amplitudes were significantly different between Pre and Day 21 are shown with asterisks (*).