Spontaneous cellular vibrations in the guinea-pig temporal-bone preparation

Area of Science:

• Otoacoustic Emissions
• Auditory Physiology
• Cellular Mechanics

Background:

• Hensen cells play a crucial role in auditory transduction.
• Spontaneous otoacoustic emissions (SOAEs) are sounds emitted by the ear without external stimulation.
• The precise origin of SOAEs remains a subject of investigation.

Purpose of the Study:

• To investigate the presence and characteristics of spontaneous mechanical vibrations in Hensen cells.
• To determine the relationship between spontaneous vibrations and otoacoustic emissions.

Main Methods:

• Utilized a laser-heterodyne interferometer to measure mechanical vibrations of Hensen cells in a guinea-pig temporal-bone preparation.
• Recorded velocity versus time waveforms from individual cells.
• Constructed smoothed periodograms (spectral-density estimates versus frequency) from the recorded data.

Main Results:

• Detected spontaneous mechanical vibrations in Hensen cells, with several peaks significantly above the noise floor.
• Observed that vibration frequencies varied between preparations, ruling out ambient noise as the cause.
• Found that vibrations were present only in fresh preparations and correlated with the tuning curve characteristics of the cells.
• Identified spontaneous vibration peaks within the principal peak region of the cells' tuning curves.

Conclusions:

• Spontaneous mechanical vibrations in Hensen cells are a real phenomenon, not an artifact of external noise.
• These vibrations are likely generated by outer hair cells.
• The study proposes that these spontaneous Hensen cell vibrations are the source of spontaneous otoacoustic emissions.