Simultaneous multielectrode recordings along the human scala tympani: Evidence for level-dependent place coding

Area of Science:

• Auditory Neuroscience
• Human Physiology
• Bioacoustics

Background:

• The cochlea's tonotopic map encodes sound frequency and intensity.
• How sound intensity influences this map in humans is not fully understood.
• Animal models show intensity-dependent shifts, but human data is limited.

Purpose of the Study:

• To investigate intensity-dependent changes in human cochlear place coding.
• To characterize shifts in tonotopic organization with varying sound intensities.
• To provide physiological evidence for intensity effects on human auditory processing.

Main Methods:

• Simultaneous multielectrode electrocochleography recordings in the human scala tympani.
• Measurements in subjects with preserved cochlear mechanics, including auditory neuropathy spectrum disorder patients and normal-hearing individuals.
• Quantification of cochlear traveling-wave velocity and spatial activation patterns.

Main Results:

• Observed pronounced basalward shifts (up to ~158°) in best-frequency responses at higher sound intensities.
• Demonstrated broader spatial activation with increasing intensity.
• Found that traveling wave velocity and phase response remained stable across intensities despite altered spatial patterns.

Conclusions:

• Established physiological evidence for systematic changes in human cochlear frequency representation with sound intensity.
• Revealed intensity-dependent shifts in tonotopic organization in the human cochlea.
• Provided crucial insights into fundamental auditory coding mechanisms.