Predicting the location of missing outer hair cells using the electrical signal recorded at the round window

Abstract

The electrical signal recorded at the round window was used to estimate the location of missing outer hair cells. The cochlear response was recorded to a low frequency tone embedded in high-pass filtered noise conditions. Cochlear damage was created by either overexposure to frequency-specific tones or laser light. In animals with continuous damage along the partition, the amplitude of the cochlear response increased as the high-pass cutoff frequency increased, eventually reaching a plateau. The cochlear distance at the onset of the plateau correlated with the anatomical onset of outer hair cell loss. A mathematical model replicated the physiologic data but was limited to cases with continuous hair cell loss in the middle and basal turns. The neural contribution to the cochlear response was determined by recording the response before and after application of Ouabain. Application of Ouabain eliminated or reduced auditory neural activity from approximately two turns of the cochlea. The amplitude of the cochlear response was reduced for moderate signal levels with a limited effect at higher levels, indicating that the cochlear response was dominated by outer hair cell currents at high signal levels and neural potentials at low to moderate signal levels.

The potential use of low-frequency tones to locate regions of outer hair cell loss

“…The response, however, is still dominated by basal hair cells near the electrode, which can confound an attempt to measure outer hair cell (OHC) health at the apex of the cochlea (Dallos, 1969; Patuzzi et al, 1989). To solve this problem, Chertoff et al (2012, 2014) implemented a filtered noise paradigm in which 733 & 762 Hz tone stimuli were embedded in high-pass filtered noise with seventeen consecutively increasing cutoff frequencies, allowing them to measure a cumulative response from seventeen corresponding regions along the length of the cochlear partition. Taking into account the electric field decay and geometric distance from each point of measurement to the electrode, they modeled a growth function of the CM amplitude as a function of distance along the length of the cochlear partition.…”

“…Taking into account the electric field decay and geometric distance from each point of measurement to the electrode, they modeled a growth function of the CM amplitude as a function of distance along the length of the cochlear partition. This growth function was deemed the cumulative amplitude function (CAF), and they showed that damage to OHCs will alter the growth of this function (Chertoff et al, 2012, 2014). …”

“…The first is that the literature suggests that a significant proportion of the RW response is generated from auditory nerve potentials in addition to OHCs, especially for low-frequency stimuli (Henry, 1995; Patuzzi et al, 1989; He et al, 2012; Lichtenhan et al, 2014). In order to quantify the proportion of neural and OHC potentials present in the RW response, or cochlear response (CR), Chertoff et al (2014) damaged the auditory nerve with 10 mM of an ototoxic drug, ouabain, and recorded the CR before and after an acute application to the RW niche. Chertoff et al (2014) reported reductions in CR amplitude to a 762 Hz tone of up to 70% (at low signal levels) after the application of 10 mM ouabain on the RW for 30 min.…”

“…In order to quantify the proportion of neural and OHC potentials present in the RW response, or cochlear response (CR), Chertoff et al (2014) damaged the auditory nerve with 10 mM of an ototoxic drug, ouabain, and recorded the CR before and after an acute application to the RW niche. Chertoff et al (2014) reported reductions in CR amplitude to a 762 Hz tone of up to 70% (at low signal levels) after the application of 10 mM ouabain on the RW for 30 min. They attributed the effect primarily to the loss of basal auditory nerve fibers; however, they also found a small decrease in distortion-product otoacoustic emission (DPOAE) amplitudes to a 24 kHz primary tone, indicating some OHC damage.…”

An analysis of cochlear response harmonics: Contribution of neural excitation

“…Ouabain was dissolved in AP. The composition of gerbil AP (mM) was NaCl (120), KCl (3.5), CaCl 2 (1.5), glucose (5.5), HEPES (20), and the pH was adjusted to 7.5 with NaOH (Chertoff et al, 2014). Procedures were approved by the Animal Care and Use Committee at the University of Kansas Medical Center.…”