Electrically evoked otoacoustic emissions from the chicken ear

Area of Science:

• Auditory Neuroscience
• Otoacoustic Emissions Research
• Comparative Bioacoustics

Background:

• Mammalian outer hair cell electromotility underlies inner ear sensitivity and otoacoustic emissions (OAEs).
• Avian ears are sensitive and produce OAEs, but lack somatic electromotility in hair cells.
• Stereocilia bundle movements in avian hair cells suggest a potential mechanism for electrically evoked OAEs.

Purpose of the Study:

• To investigate if electrically evoked otoacoustic emissions (EEOAEs) can be generated in avian ears.
• To explore the biological origin and characteristics of EEOAEs in the chicken cochlea.

Main Methods:

• Application of alternating current (AC) to the chicken's round window to evoke EEOAEs.
• Analysis of EEOAE frequency response and impulse response to current pulses.
• Assessment of EEOAEs and distortion product OAEs following cochlear damage (anoxia, paraformaldehyde) and hair cell loss (kanamycin).

Main Results:

• AC current stimulation evoked EEOAEs in chickens, with peak amplitudes between 1000-3000 Hz.
• EEOAEs exhibited a bandpass frequency response and oscillatory impulse response.
• Cochlear damage and hair cell loss significantly reduced EEOAEs and distortion product OAEs, indicating a biological origin.

Conclusions:

• The study demonstrates EEOAEs in avian species, challenging the mammalian model of outer hair cell electromotility.
• Results strongly suggest a biological basis for avian EEOAEs, likely involving electrically evoked stereocilia bundle movements.
• This finding opens new avenues for understanding auditory function and OAE generation across different vertebrate species.