Central Auditory Gain Secondary to Hearing Deprivation and Its Role in Hyperacusis

Abstract

Objectives:

Determine the characteristics of the auditory central gain due to bilateral hearing deprivation, and its relationship with circadian variations as a function of cortical activity.

Methods:

The study was designed as a prospective observational research, in a national referral center. A total of 28 volunteers ranging between 18 and 30 years old underwent bilateral earplugging with Merocel, previous medical examination, anthropometry, author developed questionnaire, Hamilton anxiety and depression inventory, speech and pure tone audiometry, tympanometry and middle ear reflex (MER), distortion products otoacoustics emissions input/output(DPOAE-I/O), and uncomfortable loudness levels (ULLs) in 0.5-4 kHz. Subjects were randomly divided in 2 groups: Group A, starting at 8:00 am and finishing at 8:00 pm; Group B, starting at 4:00 pm ending at 4:00 am. Serum cortisol levels and audiological test were obtained at the beginning and at the end of the session. A 24-hour free urinary cortisol levels were measured.

Results:

We observed an air conduction drop in right ears (AD) at 1 kHz (P = .036) and 0.125, 4 y 8 kHz frequencies in left ears(AS) (P = .013, .003, .003), respectively. The ULLs in Group A showed a decline in AD/AS thresholds in all frequencies. Contralateral AD MER thresholds presented a decline on 0.5 to 1 kHz. AS DPOAE-I/O fell by 25 and 45 dB (P = .046, .461) in group B, and 25 dB in Group A (P = .047). In group B, serum cortisol levels increased by 19.28 ± 4.37 µg/µL (P = .018).

Conclusions:

We report an association between the increase of serum cortisol and auditory gain and an indirect relationship with normal cortical activity. Thus, bilateral hearing deprivation can potentially be used as a convenient model for the study of hyperacusis.