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1.  Spatial Irregularities of Sensitivity along the Organ of Corti of the Cochlea 
The Journal of Neuroscience  2014;34(34):11349-11354.
Fine structures of spatial profiles were computed from existing records of cat and chinchilla auditory-nerve fibers on the basis of their characteristic frequencies and cochlear maps. The spatial fine structures of characteristic-frequency thresholds and of “spontaneous” and driven firing rates were mutually correlated, implying the presence of sensitivity fluctuations due to spatial irregularities of presynaptic structures or processes of the inner hair cells and their input. These findings suggest that activity that appears spontaneous is not actually spontaneous and may indicate irregularities of tonotopic mapping in cochlear mechanics.
doi:10.1523/JNEUROSCI.2558-13.2014
PMCID: PMC4138343  PMID: 25143615
auditory-nerve fibers; cochlea; inner hair cells; organ of Corti; spatial irregularities
2.  Frequency Tuning of Basilar Membrane and Auditory Nerve Fibers in the Same Cochleae 
Science (New York, N.Y.)  1998;282(5395):1882-1884.
Responses to tones of a basilar membrane site and of auditory nerve fibers innervating neighboring inner hair cells were recorded in the same cochleae in chinchillas. At near-threshold stimulus levels, the frequency tuning of auditory nerve fibers closely paralleled that of basilar membrane displacement modified by high-pass filtering, indicating that only relatively minor signal transformations intervene between mechanical vibration and auditory nerve excitation. This finding establishes that cochlear frequency selectivity in chinchillas (and probably in mammals in general) is fully expressed in the vibrations of the basilar membrane and renders unnecessary additional (“second”) filters, such as those present in the hair cells of the cochleae of reptiles.
PMCID: PMC3578392  PMID: 9836636
3.  Low-frequency suppression of auditory nerve responses to characteristic frequency tones 
Hearing research  1997;113(1-2):29-56.
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.
PMCID: PMC3578423  PMID: 9387984
Auditory nerve; Biasing; Modulation; Rate suppression; Basilar membrane; Inner hair cells; Cochlea; Chinchilla
4.  Traveling waves on the organ of Corti of the chinchilla cochlea: spatial trajectories of inner hair cell depolarization inferred from responses of auditory-nerve fibers 
Spatial magnitude and phase profiles for inner hair cell depolarization throughout the chinchilla cochlea were inferred from responses of auditory-nerve fibers to threshold- and moderate-level tones and tone complexes. Firing-rate profiles for frequencies ≤ 2 kHz are bimodal, with the major peak at the characteristic place and a secondary peak at 3–5 mm from the extreme base. Response-phase trajectories are synchronous with peak outward stapes displacement at the extreme cochlear base and accumulate 1.5-period lags at the characteristic places. High-frequency phase trajectories are very similar to the trajectories of basilar-membrane peak velocity toward scala tympani. Low-frequency phase trajectories undergo a polarity flip in a region, 6.5–9 mm from the cochlear base, where traveling-wave phase velocity attains a local minimum and a local maximum and where the onset latencies of near-threshold impulse responses computed from responses to near-threshold white noise exhibit a local minimum. That region is the same where frequency-threshold tuning curves of auditory-nerve fibers undergo a shape transition. Since depolarization of inner hair cells presumably indicates the mechanical stimulus to their stereocilia, the present results suggest that distinct low-frequency forward waves of organ of Corti vibration are launched simultaneously at the extreme base of the cochlea and at the 6.5–9 mm transition region, from where antiphasic reflections arise.
doi:10.1523/JNEUROSCI.1138-12.2012
PMCID: PMC3436599  PMID: 22855802
5.  Timing of cochlear responses inferred from frequency-threshold tuning curves of auditory-nerve fibers 
Hearing research  2010;272(1-2):178-186.
Links between frequency tuning and timing were explored in the responses to sound of auditory-nerve fibers. Synthetic transfer functions were constructed by combining filter functions, derived via minimum-phase computations from average frequency-threshold tuning curves of chinchilla auditory-nerve fibers with high spontaneous activity (A. N. Temchin et al., J. Neurophysiol. 100: 2889–2898, 2008), and signal-front delays specified by the latencies of basilar-membrane and auditory-nerve fiber responses to intense clicks (A. N. Temchin et al., J. Neurophysiol. 93: 3635–3648, 2005). The transfer functions predict several features of the phase-frequency curves of cochlear responses to tones, including their shape transitions in the regions with characteristic frequencies of 1 kHz and 3–4 kHz (A. N. Temchin and M. A. Ruggero, JARO 11: 297–318, 2010). The transfer functions also predict the shapes of cochlear impulse responses, including the polarities of their frequency sweeps and their transition at characteristic frequencies around 1 kHz. Predictions are especially accurate for characteristic frequencies < 1 kHz.
doi:10.1016/j.heares.2010.10.002
PMCID: PMC3039049  PMID: 20951191
6.  Phase-Locked Responses to Tones of Chinchilla Auditory Nerve Fibers: Implications for Apical Cochlear Mechanics 
Responses to tones with frequency ≤ 5 kHz were recorded from auditory nerve fibers (ANFs) of anesthetized chinchillas. With increasing stimulus level, discharge rate–frequency functions shift toward higher and lower frequencies, respectively, for ANFs with characteristic frequencies (CFs) lower and higher than ∼0.9 kHz. With increasing frequency separation from CF, rate–level functions are less steep and/or saturate at lower rates than at CF, indicating a CF-specific nonlinearity. The strength of phase locking has lower high-frequency cutoffs for CFs >4 kHz than for CFs < 3 kHz. Phase–frequency functions of ANFs with CFs lower and higher than ∼0.9 kHz have inflections, respectively, at frequencies higher and lower than CF. For CFs >2 kHz, the inflections coincide with the tip-tail transitions of threshold tuning curves. ANF responses to CF tones exhibit cumulative phase lags of 1.5 periods for CFs 0.7–3 kHz and lesser amounts for lower CFs. With increases of stimulus level, responses increasingly lag (lead) lower-level responses at frequencies lower (higher) than CF, so that group delays are maximal at, or slightly above, CF. The CF-specific magnitude and phase nonlinearities of ANFs with CFs < 2.5 kHz span their entire response bandwidths. Several properties of ANFs undergo sharp transitions in the cochlear region with CFs 2–5 kHz. Overall, the responses of chinchilla ANFs resemble those in other mammalian species but contrast with available measurements of apical cochlear vibrations in chinchilla, implying that either the latter are flawed or that a nonlinear “second filter” is interposed between vibrations and ANF excitation.
doi:10.1007/s10162-009-0197-4
PMCID: PMC2862913  PMID: 19921334
basilar membrane; cochlear apex; phase–frequency functions; rate–frequency functions
7.  Basilar Membrane Vibrations Near the Round Window of the Gerbil Cochlea 
Using a laser velocimeter, responses to tones were measured at a basilar membrane site located about 1.2 mm from the extreme basal end of the gerbil cochlea. In two exceptional cochleae in which function was only moderately disrupted by surgical preparations, basilar membrane responses had characteristic frequencies (CFs) of 34–37 kHz and exhibited a CF-specific compressive nonlinearity: Sensitivity near the CF decreased systematically and the response peaks shifted toward lower frequencies with increasing stimulus level. Response phases also changed with increases in stimulus level, exhibiting small relative lags and leads at frequencies just lower and higher than CF, respectively. Basilar membrane responses to low-level CF tones exceeded the magnitude of stapes vibrations by 54–56 dB. Response phases led stapes vibrations by about 90° at low stimulus frequencies; at higher frequencies, basilar membrane responses increasingly lagged stapes vibration, accumulating 1.5 periods of phase lag at CF. Postmortem, nonlinearities were abolished and responses peaked at ~0.5 octave below CF, with phases which lagged and led in vivo responses at frequencies lower and higher than CF, respectively. In conclusion, basilar membrane responses near the round window of the gerbil cochlea closely resemble those for other basal cochlear sites in gerbil and other species.
doi:10.1007/sl01620020023
PMCID: PMC1868570  PMID: 12382108
inner ear; auditory; basilar membrane; cochlear mechanics; compressive nonlinearity
8.  High-Frequency Sensitivity of the Mature Gerbil Cochlea and Its Development 
Audiology & neuro-otology  2003;8(1):19-27.
The thresholds of compound action potentials evoked by tone pips were measured in the cochleae of anesthetized gerbils, both in adults and in neonates aged 14, 16, 18, 20 and 30 days, using round-window electrodes. Stapes vibrations were also measured, using a laser velocimeter, in many of the same ears of adults and neonates aged 14, 16, 18 and 20 days to assess cochlear sensitivity in isolation from middle ear effects and to circumvent problems associated with calibration of acoustic stimuli at high frequencies. Whether referenced to sound pressure level in the ear canal or stapes vibration velocity, thresholds in adults were roughly uniform in the entire range of tested frequencies, 1.25–38.5 kHz. In neonates, thresholds decreased systematically as a function of age, with the largest reductions occurring at the highest frequencies. Thresholds remained slightly immature at all frequencies 30 days after birth. The results for adult gerbils are consistent with the recent finding that basilar-membrane responses to characteristic frequency tones normalized to stapes vibrations are as sensitive at sites near the round window as at more apical sites. The results for neonates confirm that the extreme basal region of the cochlea is the last to approach maturity, with substantial development occurring between 20 and 30 days after birth.
doi:10.1159/000067892
PMCID: PMC1868568  PMID: 12566689
Cochlea; Basilar membrane; Development; Middle ear; Stapes; Gerbil
9.  Middle-ear transmission in humans: wide-band, not frequency-tuned? 
Postmortem and in vivo vibration responses to sound of the stapes and the umbo of human ears are surveyed. The magnitudes of umbo velocity responses recorded postmortem decay between 1 and 5 or 10 kHz at rates between 0 and −3 dB/octave. In contrast, the magnitudes of in vivo umbo vibration are relatively invariant over a wide frequency range, amply exceeding the bandwidth of the audiogram according to one report. Similarly, most studies of postmortem stapes vibration report velocities tuned to about 1 kHz, with magnitudes that decay at a rate of about −6 dB/octave at higher frequencies. In contrast, in vivo stapes responses are apparently only mildly tuned. We conjecture that the bandwidth of stapes vibration velocity in humans will eventually be shown to exceed the bandwidth of the audiogram, in line with findings in other amniotic vertebrates.
doi:10.1121/1.1566924
PMCID: PMC1868690  PMID: 17505561
10.  Similarity of Traveling-Wave Delays in the Hearing Organs of Humans and Other Tetrapods 
Transduction of sound in mammalian ears is mediated by basilar-membrane waves exhibiting delays that increase systematically with distance from the cochlear base. Most contemporary accounts of such “traveling-wave” delays in humans have ignored postmortem basilar-membrane measurements in favor of indirect in vivo estimates derived from brainstem-evoked responses, compound action potentials, and otoacoustic emissions. Here, we show that those indirect delay estimates are either flawed or inadequately calibrated. In particular, we argue against assertions based on indirect estimates that basilar-membrane delays are much longer in humans than in experimental animals. We also estimate in vivo basilar-membrane delays in humans by correcting postmortem measurements in humans according to the effects of death on basilar-membrane vibrations in other mammalian species. The estimated in vivo basilar-membrane delays in humans are similar to delays in the hearing organs of other tetrapods, including those in which basilar membranes do not sustain traveling waves or that lack basilar membranes altogether.
doi:10.1007/s10162-007-0081-z
PMCID: PMC1868567  PMID: 17401604
cochlea; basilar membrane; auditory; otoacoustic emissions; compound action potentials; brainstem evoked responses
11.  Wiener Kernels of Chinchilla Auditory-Nerve Fibers: Verification Using Responses to Tones, Clicks, and Noise and Comparison With Basilar-Membrane Vibrations 
Journal of neurophysiology  2005;93(6):3635-3648.
Responses to tones, clicks, and noise were recorded from chinchilla auditory-nerve fibers (ANFs). The responses to noise were analyzed by computing the zeroth-, first-, and second-order Wiener kernels (h0, h1, and h2). The h1s correctly predicted the frequency tuning and phases of responses to tones of ANFs with low characteristic frequency (CF). The h2s correctly predicted the frequency tuning and phases of responses to tones of all ANFs, regardless of CF. Also regardless of CF, the kernels jointly predicted about 77% of the features of ANF responses to “frozen” samples of noise. Near-CF group delays of kernels and signal-front delays of responses to intense rarefaction clicks exceeded by 1 ms the corresponding basilar-membrane delays at both apical and basal sites of the chinchilla cochlea. This result, confirming that synaptic and neural processes amount to 1 ms regardless of CF, permitted drawing a map of basilar-membrane delay as a function of position for the entire length of the chinchilla cochlea, a first for amniotic species.
doi:10.1152/jn.00885.2004
PMCID: PMC1876724  PMID: 15659530
12.  Similarity of Traveling-Wave Delays in the Hearing Organs of Humans and Other Tetrapods 
Transduction of sound in mammalian ears is mediated by basilar-membrane waves exhibiting delays that increase systematically with distance from the cochlear base. Most contemporary accounts of such “traveling-wave” delays in humans have ignored postmortem basilar-membrane measurements in favor of indirect in vivo estimates derived from brainstem-evoked responses, compound action potentials, and otoacoustic emissions. Here, we show that those indirect delay estimates are either flawed or inadequately calibrated. In particular, we argue against assertions based on indirect estimates that basilar-membrane delays are much longer in humans than in experimental animals. We also estimate in vivo basilar-membrane delays in humans by correcting postmortem measurements in humans according to the effects of death on basilar-membrane vibrations in other mammalian species. The estimated in vivo basilar-membrane delays in humans are similar to delays in the hearing organs of other tetrapods, including those in which basilar membranes do not sustain traveling waves or that lack basilar membranes altogether.
doi:10.1007/s10162-007-0081-z
PMCID: PMC1868567  PMID: 17401604
cochlea; basilar membrane; auditory; otoacoustic emissions; compound action potentials; brainstem evoked responses
13.  Similarity of Traveling-Wave Delays in the Hearing Organs of Humans and Other Tetrapods 
Transduction of sound in mammalian ears is mediated by basilar-membrane waves exhibiting delays that increase systematically with distance from the cochlear base. Most contemporary accounts of such “traveling-wave” delays in humans have ignored postmortem basilar-membrane measurements in favor of indirect in vivo estimates derived from brainstem-evoked responses, compound action potentials, and otoacoustic emissions. Here, we show that those indirect delay estimates are either flawed or inadequately calibrated. In particular, we argue against assertions based on indirect estimates that basilar-membrane delays are much longer in humans than in experimental animals. We also estimate in vivo basilar-membrane delays in humans by correcting postmortem measurements in humans according to the effects of death on basilar-membrane vibrations in other mammalian species. The estimated in vivo basilar-membrane delays in humans are similar to delays in the hearing organs of other tetrapods, including those in which basilar membranes do not sustain traveling waves or that lack basilar membranes altogether.
doi:10.1007/s10162-007-0081-z
PMCID: PMC1868567  PMID: 17401604
cochlea; basilar membrane; auditory; otoacoustic emissions; compound action potentials; brainstem evoked responses
14.  Basilar Membrane Vibrations Near the Round Window of the Gerbil Cochlea 
Using a laser velocimeter, responses to tones were measured at a basilar membrane site located about 1.2 mm from the extreme basal end of the gerbil cochlea. In two exceptional cochleae in which function was only moderately disrupted by surgical preparations, basilar membrane responses had characteristic frequencies (CFs) of 34–37 kHz and exhibited a CF-specific compressive nonlinearity: Sensitivity near the CF decreased systematically and the response peaks shifted toward lower frequencies with increasing stimulus level. Response phases also changed with increases in stimulus level, exhibiting small relative lags and leads at frequencies just lower and higher than CF, respectively. Basilar membrane responses to low-level CF tones exceeded the magnitude of stapes vibrations by 54–56 dB. Response phases led stapes vibrations by about 90° at low stimulus frequencies; at higher frequencies, basilar membrane responses increasingly lagged stapes vibration, accumulating 1.5 periods of phase lag at CF. Postmortem, nonlinearities were abolished and responses peaked at ~0.5 octave below CF, with phases which lagged and led in vivo responses at frequencies lower and higher than CF, respectively. In conclusion, basilar membrane responses near the round window of the gerbil cochlea closely resemble those for other basal cochlear sites in gerbil and other species.
doi:10.1007/s101620020023
PMCID: PMC1868570  PMID: 12382108

Results 1-14 (14)