Two-tone suppression by a saturating feedback model of the cochlear partition

doi:10.1016/0378-5955(92)90086-3

Hearing Research

Volume 63, Issues 1–2, November 1992, Pages 203-210

https://doi.org/10.1016/0378-5955(92)90086-3 Get rights and content

Abstract

A model of a small strip of cochlear partition was computer simulated. The model is composed of two elements, approximations to the transfer functions of an inner hair cell (IHC) and an outer hair cell (OHC), respectively. The IHC element was insensitive to DC stimulation. Input was one or two sinusoids. One sinusoid, at the characteristic frequency (CF), was multiplied by the gain of the ‘cochlear amplifier’. A second sinusoid, representing a tone with much lower frequency, was not affected by the amplifier gain. This gain was determined by the OHC transfer function. In one form of the model (‘fixed-gain’), this gain was set at a fixed number determined from the furthest point reached on the OHC transfer function. This form of the model produced very realistic single-tone responses as well as showing ‘two-tone suppression’: that is, the IHC DC response produced by CF stimulation was reduced when the lower-frequency sinusoid, at suitable intensities, was added to the stimulus. When a DC component was added to the two-tone stimulus, the magnitude of this two-tone suppression was enhanced. In the second form of the model (‘variable-gain’), the cochlear-amplifier gain varied throughout the stimulus cycle. Its value was re-calculated at each instant, determined by the point on the OHC transfer function current at that particular instant. This form of the model showed two-tone suppression only when a DC component was added to the two-tone stimulus.

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Cited by (13)

Effect of the attachment of the tectorial membrane on cochlear micromechanics and two-tone suppression
2014, Biophysical Journal
The mechanical stimulation of the outer hair cell hair bundle (HB) is a key step in nonlinear cochlear amplification. We show how two-tone suppression (TTS), a hallmark of cochlear nonlinearity, can be used as an indirect measure of HB stimulation. Using two different nonlinear computational models of the cochlea, we investigate the effect of altering the mechanical load applied by the tectorial membrane (TM) on the outer hair cell HB. In the first model (TM-A model), the TM is attached to the spiral limbus (as in wild-type animals); in the second model (TM-D model), the TM is detached from the spiral limbus (mimicking the cochlea of Otoa^EGFP/EGFP mutant mice). As in recent experiments, model simulations demonstrate that the absence of the TM attachment does not preclude cochlear amplification. However, detaching the TM alters the mechanical load applied by the TM on the HB at low frequencies and therefore affects TTS by low-frequency suppressors. For low-frequency suppressors, the suppression threshold obtained with the TM-A model corresponds to a constant suppressor displacement on the basilar membrane (as in experiments with wild-type animals), whereas it corresponds to a constant suppressor velocity with the TM-D model. The predictions with the TM-D model could be tested by measuring TTS on the basilar membrane of the Otoa^EGFP/EGFP mice to improve our understanding of the fundamental workings of the cochlea.
Low-frequency suppression of auditory nerve responses to characteristic frequency tones
1997, Hearing Research
The effects of low-frequency (50, 100, 200 and 400 Hz) ‘suppressor’ tones on responses to moderate-level characteristic frequency (CF) tones were measured in chinchilla auditory nerve fibers. Two-tone interactions were evident at suppressor intensities of 70–100 dB SPL. In this range, the average response rate decreased as a function of increasing suppressor level and the instantaneous response rate was modulated periodically. At suppression threshold, the phase of suppression typically coincided with basilar membrane displacement toward scala tympani, regardless of CF. At higher suppressor levels, two suppression maxima coexisted, synchronous with peak basilar membrane displacement toward scala tympani and scala vestibuli. Modulation and rate-suppression thresholds did not vary as a function of spontaneous activity and were only minimally correlated with fiber sensitivity. Except for fibers with CF<1 kHz, modulation and rate-suppression thresholds were lower than rate and phase-locking thresholds for the suppressor tones presented alone. In the case of high-CF fibers with low spontaneous activity, excitation thresholds could exceed suppression thresholds by more than 30 dB. The strength of modulation decreased systematically with increasing suppressor frequency. For a given suppressor frequency, modulation was strongest in high-CF fibers and weakest in low-CF fibers. The present findings strongly support the notion that low-frequency suppression in auditory nerve fibers largely reflects an underlying basilar membrane phenomenon closely related to compressive non-linearity.
Low-frequency modulation of inner hair cell and organ of Corti responses in the guinea pig cochlea
1997, Hearing Research
Low-frequency tones are used to study changes in responsiveness as a function of phase in inner hair cell (IHC) and organ of Corti (OC) responses recorded from second turn of the guinea pig cochlea. In these experiments a 40 Hz stimulus is combined with a variable frequency probe to determine the degree to which tones at and below best frequency (BF) are modulated. Changes in responsiveness produced by the low-frequency input are quantified and related to position of the basilar membrane which is estimated using the phase of the cochlear microphonic measured in the OC fluid space. Results obtained when 40 Hz is presented at its lowest effective level demonstrate that ac responses to low-level BF probes are reduced for basilar membrane displacements to scala tympani while probe tones well below BF are modulated in the opposite direction. The transition between these two response patterns occurs when the overall DC produced in the OC by the two-tone input changes from positive to negative. Because of this association, the frequency dependence exhibited in the bias results may be linked to mechanisms responsible for generating the two polarities of the summating potential and the DC receptor potentials that it reflects. An attempt is also made to relate bias-induced changes in hair cell receptor potentials to modulations in single-unit rate responses. In other words, to address variations in the temporal relationships between excitation and suppression measured in the auditory nerve.
Suppression in auditory-nerve fibers of cats using low-side suppressors. I. Temporal aspects
1996, Hearing Research
Two-tone suppression was studied in the auditory nerve fibers of anesthetized cats, using low-frequency suppressors (50–2000 Hz). The response to the characteristic-frequency (CF) tone was suppressed in a phase-specific manner, attaining one or two minimums in 1 cycle of the suppressor (SUP) tone. The suppression phase-lead (i.e., the phase of maximum suppression leading the phase of response to the SUP tone) was about $14$ cycle for lower-frequency suppressors (50, 100 and 200 Hz), and was close to $12$ cycle for higher-frequency suppressors (500, 1000 and 2000 Hz). Both the phase of suppression and the suppression phase-lead are independent of fiber spontaneous rate (SR). Some fibers also show a secondary (minor) suppression at higher SUP intensities, which is always about $12$ cycle away from the first (major) one. Fibers with higher CFs (> 2 kHz) are more likely to show a secondary suppression than those with lower CFs. The threshold difference between the major and minor suppressions is CF-dependent: lower CF fibers usually show differences of 10 dB or greater, while higher CF fibers show smaller differences. The secondary suppression is suppressor-frequency-dependent, usually restricted to lower-frequency suppressors (⪯ 200 Hz). No fibers showed a secondary suppression with a SUP frequency 1000 Hz or greater. The phases of suppressions (both the major and minor suppressions) are not affected by the intensity of the CF tone. Non-excitatory, low-frequency suppressors can also give rise to significant suppression. The threshold of synchronization to the SUP tone in the two-tone part was usually the lowest, while the SUP-alone rate threshold was highest. The threshold of synchronization in the SUP-alone segment and threshold of suppression were in between. In some low-SR fibers, complete suppression can be seen.
Suppression in auditory-nerve fibers of cats using low-side suppressors. III. Model results
1996, Hearing Research
A phenomenological model which simulates auditory-nerve (AN) two-tone suppression was developed. The model uses the output of the outer hair cell WHO to control the gain of the cochlear amplifier, which presumably affects only frequencies near the characteristic frequency (CF). Among other things, the model can simulate basic AN suppression patterns including the $14$ to $12$ cycle relationships which exist between phase of suppression and phase of excitation to the suppressor (SUP) tone alone (Cai and Geisler, 1996a). Without any changes, it is also able to simulate the experimental low-frequency biasing data and the suppression of CF component by the low-frequency SUP tone in the OHC outputs (Cheatham and Dallos, 1994). These successful simulations of the suppression patterns support the basic assumption in the model, that the saturation of OHC transduction current produces two-tone suppression. However, the amplitude behavior of the model fits that obtained only from AN fibers with high spontaneous rates (and from inner hair cells (IHC)), but not fibers with lower spontaneous rates. It appears, therefore, that other unknown mechanism(s) operating at stages following the IHC potential are important in determining the magnitude of low-side suppression.
Early events in auditory processing
1993, Current Opinion in Neurobiology

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Two-tone suppression by a saturating feedback model of the cochlear partition

Abstract

Neurosci. Let.

Hear. Res.

Hear. Res.

Hear. Res.

Hear. Res.

Hearing Res.

Hearing Res.

Hear. Res.

Properties of ‘two-tone inhibition’ in primary auditory neurones

J. Physiol. (London)

Changes in the phase of excitortone responses in cat auditory-nerve fibers by suppressor tones and fatigue

J. Acoust. Soc. Am.

Inner hair cell responses to tonal stimulation in the presence of broadband noise

J. Acoust. Soc. Am.

Two-tone suppression in a nonlinear model of the hasikir membrane

J. Acoust. Soc. Am.

Two-tone suppression, excitalion and the alter effect in rate responses in auditory nerve fibres in the cat

Hearing Res.

Coding of information pertaining to paired low-frequency tones in single auditory nerve fibers of the squirrel monkey

J. Neurophysiol.