Cochlear transducer operating point adaptation.
The operating point (OP) of outer hair cell (OHC) mechanotransduction can be defined as any shift away from the center position on the transduction function. It is a dc offset that can be described by percentage of the maximum transduction current or as an equivalent dc pressure in the ear canal. The change of OP can be determined from the changes of the second and third harmonics of the cochlear microphonic (CM) following a calibration of its initial value. We found that the initial OP was dependent on sound level and cochlear sensitivity. From CM generated by a lower sound level at 74 dB SPL to avoid saturation and suppression of basal turn cochlear amplification, the OHC OP was at constant 57% of the maximum transduction current (an ear canal pressure of -0.1 Pa). To perturb the OP, a constant force was applied to the bony shell of the cochlea at the 18 kHz best frequency location using a blunt probe. The force applied over the scala tympani induced an OP change as if the organ of Corti moved toward the scala vestibuli (SV) direction. During an application of the constant force, the second harmonic of the CM partially recovered toward the initial level, which could be described by two time constants. Removing the force induced recovery of the second harmonic to its normal level described by a single time constant. The force applied over the SV caused an opposite result. These data indicate an active mechanism for OHC transduction OP.
Zou
Yuan
Y
Oregon Hearing Research Center, NRC04, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239-3098, USA.
Zheng
Jiefu
J
Ren
Tianying
T
Nuttall
Alfred
A
D000161:Acoustic Stimulation; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D001489:Basilar Membrane / Q000502:physiology; D002923:Cilia / Q000502:physiology; D003051:Cochlea / Q000502:physiology*; D004424:Ear Canal / Q000502:physiology; D004711:Endolymphatic Duct / Q000502:physiology; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000502:physiology*; D008144:Loudness Perception / Q000502:physiology; D008465:Mechanoreceptors / Q000502:physiology*; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D010498:Perilymph / Q000502:physiology; D010898:Pitch Perception / Q000502:physiology; D012405:Round Window, Ear / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography