Excitation-inhibition imbalance in the auditory cortex causes sound recognition impairment in noisy environment in hidden hearing loss mice

Noise–induced hidden hearing loss (HHL) is a type of hearing dysfunction caused by moderate noise exposure. It is clinically manifested as speech recognition impairment in noisy environments while the hearing threshold remains within the normal range. The mechanism by which noise exposure causes speech recognition impairment remains unclear. This study aimed to investigate the excitation–inhibition status in the auditory cortex of HHL mice and its roles in sound recognition disability in noisy environments. A model of HHL in mice was induced using 110 decibels (dB) of helicopter noise for 2 h, the sound recognition–avoidance decision (SRAD) behavioral test was used to evaluate sound recognition ability. The activation level of excitatory neurons and the expression of vesicular glutamate transporter 1 (VGluT1) and glutamate decarboxylase 67 (GAD67) in the auditory cortex were observed. Mice were administered α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist NBQX. The results showed increased cFos expression in the auditory cortex of HHL mice and an upregulated ratio of activated CaMKⅡ⁺ neurons. Furthermore, the expression of VGluT1 and GAD67 increased in an imbalanced manner under an 80 dB noise stimulus for 2 h. The SRAD behavioral tests showed the HHL mice maintained normal sound recognition ability under quiet conditions but not in a noisy environment. The NBQX treatment improved sound recognition but did not restore normal status. This study suggested that the excitation–inhibition imbalance in the auditory cortex of mice with HHL might be the direct cause of sound recognition disorders.