Far-field cochlear microphonics in man and their relation to cochlear integrity

Area of Science:

• Audiology
• Otoacoustic Emissions
• Neuroscience

Background:

• Far-field cochlear microphonics (CM) are electrical potentials generated by cochlear hair cells.
• Current models often attribute CM generation primarily to the basal turn of the cochlea.
• Understanding CM frequency specificity is crucial for auditory function assessment.

Purpose of the Study:

• To measure far-field cochlear microphonics (CM) in humans as a function of frequency.
• To investigate the frequency-dependent characteristics of CM amplitude, dispersion, and input-output functions.
• To explore the diagnostic potential of CM measurements for evaluating cochlear health.

Main Methods:

• Phase-sensitive detection was employed to measure far-field CM.
• Measurements were conducted across a range of frequencies.
• Input-output functions were analyzed to assess cochlear response characteristics.

Main Results:

• CM amplitude, dispersion, and input-output functions exhibited periodic variations with frequency.
• Specific frequency windows were identified where CM responses were approximately frequency-specific.
• These findings contrast with the prevailing model emphasizing basal turn CM generators.
• Pathological cochleae demonstrated abnormal amplitude and phase functions.

Conclusions:

• The commonly accepted model of basal turn CM generators may require revision.
• CM measurements reveal frequency-specific characteristics and potential diagnostic windows.
• Abnormal CM patterns are indicative of cochlear pathology.
• This non-invasive technique allows for routine evaluation of hair cell function, including low-frequency speech ranges.