A behavioral measure of the cochlear changes underlying temporary threshold shifts

Area of Science:

• Audiology
• Otoacoustic emissions
• Auditory physiology

Background:

• Recreational noise exposure can lead to temporary threshold shift (TTS), a common form of hearing dysfunction.
• The specific mechanisms of TTS, particularly the roles of inner hair cells (IHCs) and outer hair cells (OHCs), require further elucidation.

Purpose of the Study:

• To investigate the contribution of outer hair cell (OHC) dysfunction to temporary threshold shift (TTS) following exposure to recreational noise.
• To differentiate the roles of inner hair cell (IHC) and outer hair cell (OHC) dysfunction in noise-induced hearing changes.

Main Methods:

• Utilized a forward-masking paradigm to assess auditory function in 18 normal-hearing adults.
• Measured hearing thresholds and estimated OHC gain before, immediately after, and one week after attending a loud music concert.
• Recorded noise exposure levels using personal dosimeters, averaging 99.0 dBA.

Main Results:

• Immediately after noise exposure, participants exhibited an average TTS of 10.8 dB at 4 kHz.
• A significant average reduction in estimated OHC gain of 11.5 dB was observed, correlating strongly with TTS.
• All auditory measures returned to pre-exposure levels within one week, indicating full recovery.

Conclusions:

• Outer hair cell (OHC) dysfunction is the primary contributor to temporary threshold shifts (TTS) induced by loud recreational noise.
• The findings highlight the susceptibility of OHCs to noise damage and their crucial role in maintaining auditory sensitivity.
• Complete recovery suggests that temporary noise exposure, within these parameters, does not cause permanent cochlear damage.