Low-frequency bias tone suppression of auditory-nerve responses to low-level clicks and tones (original) (raw)
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AIP Conference Proceedings, 2011
Apical auditory nerve (AN) fibers show two click-response regions that are both strongly inhibited by medial olivocochlear (MOC) efferents: (1) ringing responses from low-level (LL) clicks that are thought to be enhanced by a "cochlear amplifier," and (2) AN initial peak (ANIPr) responses from moderate-to-high level (~70-100 dB pSPL) rarefaction clicks. Since MOC fibers synapse and act on outer hair cells (OHCs), the MOC inhibition of these responses indicates that OHC processes are heavily involved in the production of both LL and ANIPr responses. Using AN recordings in anesthetized cats, we explored the role of OHC stereocilia position in the production of these click-response regions by presenting rarefaction clicks at different phases of 50 Hz, 70-110 dB SPL bias tones. Bias effects on LL responses followed the traditional biasing pattern of twice-abias-tone-cycle suppression with more suppression at one phase than the other. This suppression is attributable to the bias tone moving the OHC stereocilia toward low-slope, saturation regions of the mechano-electric transduction function with the rest position being closer to one saturation region. A somewhat similar pattern was found for ANIPr responses except that the bias phases of the largest suppressions were different in ANIPr versus LL responses, usually by~180 degrees. The data are consistent with the LL and ANIPr responses both being due to active processes in OHCs that are controlled by OHC stereocilia position. The different phases of the LL and ANIPr suppressions indicate that different mechanisms, and perhaps different vibration patterns in the organ of Corti, are involved in the production of LL and ANIPr responses.
Hearing Research, 2018
Recent cochlear mechanical measurements show that active processes increase the motion response of the reticular lamina (RL) at frequencies more than an octave below the local characteristic frequency (CF) for CFs above 5 kHz. A possible correlate is that in high-CF (>5 kHz) auditory-nerve (AN) fibers, responses to frequencies 1-3 octaves below CF ("tail" frequencies) can be inhibited by medial olivocochlear (MOC) efferents. These results indicate that active processes enhance the sensitivity of tail-frequency RL and AN responses. Perhaps related is that some apical low-CF AN fibers have tuning-curve (TC) "side-lobe" response areas at frequencies above and below the TC-tip that are MOC inhibited. We hypothesized that the tail and side-lobe responses are enhanced by the same active mechanisms as CF cochlear amplification. If responses to CF, tail-frequency, and TC-side-lobe tones are all enhanced by prestin motility controlled by outer-hair-cell (OHC) transmembrane voltage, then they should depend on OHC stereocilia position in the same way. To test this, we cyclically changed the OHC-stereocilia mechano-electric-transduction (MET) operating point with low-frequency "bias" tones (BTs) and increased the BT level until the BT caused quasi-static OHC MET saturation that reduced or "suppressed" the gain of OHC active processes. While measuring cat AN-fiber responses, 50 Hz BT level series, 70-120 dB SPL, were run alone and with CF tones, or 2.5 kHz tail-frequency tones, or side-lobe tones. BT-tone-alone responses were used to exclude BT sound levels that produced AN responses that might obscure BT suppression. Data were analyzed to show the BT phase that suppressed the tone responses at the lowest sound level. We found that AN responses to CF, tail-frequency, and side-lobe tones were suppressed at the same BT phase in almost all cases. The data are consistent with the enhancement of responses to CF, tail-frequency, and side-lobe tones all being due to the same OHC-stereocilia MET-dependent active process. Thus, OHC active processes enhance AN responses at frequencies outside of the cochlear-amplified TC-tip region in
The Journal of the Acoustical Society of America, 2005
Despite the insights obtained from click responses, the effects of medial-olivocochlear (MOC) efferents on click responses from single-auditory-nerve (AN) fibers have not been reported. We recorded responses of cat single AN fibers to randomized click level series with and without electrical stimulation of MOC efferents. MOC stimulation inhibited (1) the whole response at low sound levels, (2) the decaying part of the response at all sound levels, and (3) the first peak of the response at moderate to high sound levels. The first two effects were expected from previous reports using tones and are consistent with a MOC-induced reduction of cochlear amplification. The inhibition of the AN first peak, which was strongest in the apex and middle of the cochlea, was unexpected because the first peak of the classic basilar-membrane (BM) traveling wave receives little or no amplification. In the cochlear base, the click data were ambiguous, but tone data showed particularly short group delays in the tail-frequency region that is strongly inhibited by MOC efferents. Overall, the data support the hypothesis that there is a motion that bends inner-hair-cell stereocilia and can be inhibited by MOC efferents, a motion that is present through most, or all, of the cochlea and for which there is no counterpart in the classic BM traveling wave.
The Journal of the Acoustical Society of America, 1987
A displacement-sensitive capacitive probe technique was used in the first turn of guinea pig cochleas to examine whether the motion of the basilar membrane includes a displacement component analogous to the de receptor potentials of the hair cells. Such a "de" component apparently exists. At a given location on the basilar membrane, its direction toward scala vestibuli (SV) or scala tympani (ST) varies systematically with frequency of the acoustic stimulus. Furthermore, it appears to consist of two parts: a small asymmetric offset response to each gated tone burst plus a progressive shift of the basilar membrane from its previous position. The mean position shift is cumulative, increasing with successive tone bursts. The amplitude of the immediate offset response, when plotted as a function of frequency, appears to exhibit a trimodal pattern. This displacement offset is toward SV at the characteristic frequency (CF) of the location of the probe, while at frequencies either above or below the CF the offset is relatively larger, and toward ST. The mechanical motion of the basilar membrane therefore appears to contain the basis for lateral suppression. The cumulative mean position shift, however, appears to peak toward ST at the apical end of the traveling wave envelope and appears to be associated with a resonance, not of the basilar membrane motion directly, but coupled to it. The summating potential, measured concurrently at the round window, shows a more broadly tuned peak just above the CF of the position of the probe. This seems to correspond to the peak at the CF of the mechanical bias. As the preparation deteriorates, the best frequency of the vibratory displacement response decreases to about a half-octave below the original CF. There is a corresponding decrease in the frequency of the peaks of the trimodal pattern of the asymmetric responses to tone bursts. The trimodal pattern also broadens. In previous experiments the basilar membrane has been forced to move in response to a low-frequency biasing tone. The sensitivity to high-frequency stimuli varies in phase with .the biasing tone. The amplitudes of slow movement in these earlier experiments and in the present experiments are of the same order of magnitude. This suggests strongly that the cumulative shift toward ST to a high-frequency acoustic stimulus constitutes a substantial controlling bias on the sensitivity of the cochlea in that same high-frequency region. Its effect will be to reduce the slope of neural rate-level functions on the high-frequency side of CF.
The Journal of the Acoustical Society of America, 2006
Bell and Fletcher ͓J. Acoust. Soc. Am. 116, 1016-1024 ͑2004͔͒ proposed that one of the functions of activity of the outer hair cells ͑OHCs͒ might be a fluid-pumping action generating lateral fluid flow in the gap between the reticular membrane and the tectorial membrane and they supplied mathematical and descriptive justification for their theory which drew heavily upon the postulation ͑Gold, 1948͒ of the need for an active mechanism in the mammalian cochlea. In the 1970s there had been considerable speculation about how the inner hair cell ͑IHC͒ stereocilia are stimulated, whether they are stimulated in proportion to basilar membrane displacement or velocity or both, and whether the velocity dependence is due to subtectorial fluid flow. In 1977 experiments were conducted to investigate the possibility of subtectorial fluid flows using a dye as tracer. The work was not reported because it had been conducted at a time when visual observation of cochlear function had fallen out of favor in comparison with the more sensitive techniques thought necessary to observe submicroscopic phenomena, and secondly because it yielded a negative result. The essential details of those experiments are reported here to note for the record the extent to which this elaborate idea has already been tested.
The Journal of the Acoustical Society of America, 1986
The physiological basis of auditory frequency selectivity was investigated by recording the temporal response patterns of single ouchlear-nerve fibers in the cat. The characteristic frequency and sharpness of tuning was determined for low-frequency ouchlear-nerve fibers with two-tone signals whose frequency components were of equal amplitude and starting phase. The measures were compared with those obtained with sinusoidal signals. The two-tone characteristic frequency (2TCF) is deftned as the arithmetic-center frequency at which the fiber is synchronized to both signal frequencies in equal measure. The 2TCF closely corresponds to the characteristic frequency as determined by the frequency threshold curve. Moreover, the 2TCF changes relatively little (2%-12%) over a 60-dB intensity range. The 2TCF generally shifts upward with increasing intensity for ouchlear-nerve fibers tuned to frequencies below 1 kHz and shifts downward as a function of intensity for units with characteristic frequencies (CF's) above 1 kHz. The shifts in the 2TCF are considerably smaller than those observed with sinusoidal signals. Filter functions were derived from the synchronization pattern to the two-tone signal by varying the frequency of one of the components over the fiber's response area while maintaining the other component at the 2TCF. The frequency selectivity of the two-tone filter function was determined by dividing the vector strength to the variable frequency signal by the vector strength to the CF tone. The filter function was measured 10 dB down from the peak (2T Q m dB) and compared with the Q ]o dB of the frequency threshold curve. The correlation between the two measures of frequency selectivity was 0.72. The 2T Q ]o aa does change as a function of intensity. The magnitude and direction of the change is dependent on the sharpness of tuning at low and moderate sound-pressure levels (SPL's). The selectivity of the more sharply tuned fibers (2T Q •o da > 3) diminishes at intensities above 60 dB SPL. However, the broadening of selectivity is relatively small in comparison to discharge rate-based measures of selectivity. The selectivity of the more broadly tuned units remains unchanged or improves slightly at similar intensity levels. The present data indicate that the frequency selectivity and tuning of lowfrequency cochlear-nerve fibers are relatively stable over a 60-dB range of SPL's when measured in terms of their temporal discharge properties.
Hearing Research, 2011
Links between frequency tuning and timing were explored in the responses to sound of auditorynerve 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.
The Journal of the Acoustical Society of America, 1986
On the basis of comparisons of responses of guinea pig ganglion cells and inner hair cells to intense low-frequency tones, Sellick et al. [ Hear. Res. 7, 199-221 (1982) ] have proposed that basal inner hair cells can be depolarized (and thus, VIII-N. spikes generated) by the extracellular microphonic generated during hyperpolarization of outer hair cells. VIII-N. data for the chinchilla have been presented that, to a first approximation, support such a hypothesis [ Ruggero and Rich, J. Acoust. Soc. Am. 73, 2096-2108 (1983) ]. However, an apparent discrepancy exists 'in our results, vis h vis Sellick et al.'s hypothesis, in that basal fiber near-threshold responses precede maximal negativity of the round window microphonic (i.e., maximal hyperpolarization of outer hair cells) by up to 90 ø (but generally less than 45ø), depending on frequency. It is shown here that the discrepancy is resolved if certain nonlinear phase changes and overall distortion of the mierophonic waveshapes, both of which occur at intense stimulus levels, are taken into account. It is also shown that compound action potentials (AP's), superimposed on the round window microphonics, can be identified at multiple times within each stimulus cycle, closely matching the near-threshold response phases of single-unit excitation. AP 1 is nearly synchronous with the negative-to-positive transition of round window microphonics and with the excitation of fibers innervating apical-to-middle eveblear regions. AP2 is synchronous with the positive-tonegative transition of the microphonics and with the excitation of basal fibers. One or two other AP's probably reflect "peak splitting" in the responses of both basal and apical fibers.
Journal of the Acoustical Society of America, 1978
Acoustical Society of America and Acoustical Society of Japan Joint Meeting S134 x vs log f transformation however looses its validity for frequencies above the highest resonance frequency in the cochlea. For those frequencies the membrane response tends to become frequencyindependent, which yields the plateau. Hence amplitude plateaus measured in one animal at different places must begin at the same frequency, and must have a decreasing level with increasing x. This is in agreement with the experimental data. XX16. Transmission line model of cat basilar membrane. J. E. Hind
Biophysics of the cochlea II: Stationary nonlinear phenomenology
The Journal of the Acoustical Society of America, 1996
Nonlinearities affecting cochlear mechanics produce appreciable compression in the basilar membrane ͑BM͒ input/output ͑I/O͒ functions at the characteristic frequency for sound-pressure levels ͑SPLs͒ as low as 20 dB ͑re: 20 Pa͒. This is thought to depend upon saturation of the outer hair cell ͑OHC͒ mechanoelectrical transducer ͑MET͒. This hypothesis was tested by solving a nonlinear integrodifferential equation that describes the BM vibration in an active cochlea. The equation extends a previously developed linear approach ͓Mammano and Nobili, J. Acoust. Soc. Am. 93, 3320-3332 ͑1993͔͒, here modified to include saturating MET, with a few corrections mainly concerning tectorial membrane resonance and OHC coupling to the BM. Stationary solutions were computed by iteration in the frequency domain for a wide range of input SPLs, generating BM I/O functions, frequency response envelopes, and two-tone distortion products. Traveling-wave amplitude envelopes were also computed for a fixed suppressor and several suppressed tones in order to evidence the phenomenon of two-tone suppression ͑frequency masking͒ at the mechanical level. All results accord nicely with experimental data.