Biomedical subjects

N C Rich

Publications and source records attributed to N C Rich.

At least 19 recordsLinked to original sources

PubMed2004

Evaluation of actigraphy and automated telephoned questionnaires to assess hypnotic effects in insomnia.

This study aimed to explore new methodologies in insomnia research, namely whether actigraphy was suitable to show hypnotic effects over weeks in insomnia, and to compare an automated method of questionnaire data collection with traditional methods. Thirty-eight insomniacs took part in a 5-week, double-blind, placebo-controlled study of the effects of 2 weeks of administration of temazepam 20 mg on sleep. Outcome measures were actigraphy and daily St Mary's Hospital Sleep Questionnaires (SMHSQ). Actigraphy was performed using Actiwatch (CNT) and analysed using both the automated Actiwatch sleep analysis software and non-parametric analysis of rest-activity rhythms. The questionnaires were administered as straightforward pencil-and-paper for half of the time and an automated telephoned system for the other half. The experimental paradigm allowed within-subject comparison of traditional and automated data collection, both on and off drug. Actigraphy showed a high degree of inter-subject variability but, nevertheless, some sleep variables (Fragmentation Index, Actual Sleep Time %) showed significant improvement during drug treatment, and Sleep Efficiency and Actual Sleep Time were significantly worsened during the first post-drug week. Nonparametric circadian rhythm analysis showed no significant effect. Subjective data from the SMHSQ showed significant drug effects and there was no significant difference in scores between the automated and pencil-and-paper methods; automated data collection was slightly more acceptable to patients and minimized data entry and management. Effect sizes using within-subject and between-subject comparisons were calculated for the subjective and objective measures to inform future studies

Adolescent↗

PubMed1998

Basilar-membrane responses to clicks at the base of the chinchilla cochlea.

Basilar-membrane responses to clicks were measured, using laser velocimetry, at a site of the chinchilla cochlea located about 3.5 mm from the oval window (characteristic frequency or CF: typically 8-10 kHz). They consisted of relatively undamped oscillations with instantaneous frequency that increased rapidly (time constant: 200 microseconds) from a few kHz to CF. Such frequency modulation was evident regardless of stimulus level and was also present post-mortem. Responses grew linearly at low stimulus levels, but exhibited a compressive nonlinearity at higher levels. Velocity-intensity functions were almost linear near response onset but became nonlinear within 100 microseconds. Slopes could be as low as 0.1-0.2 dB/dB at later times. Hence, the response envelopes became increasingly skewed at higher stimulus levels, with their center of gravity shifting to earlier times. The phases of near-CF response components changed by nearly 180 degrees as a function of time. At high stimulus levels, this generated cancellation notches and phase jumps in the frequency spectra. With increases in click level, sharpness of tuning deteriorated and the spectral maximum shifted to lower frequencies. Response phases also changed as a function of increasing stimulus intensity, exhibiting relative lags and leads at frequencies somewhat lower and higher than CF, respectively. In most respects, the magnitude and phase frequency spectra of responses to clicks closely resembled those of responses to tones. Post-mortem responses were similar to in vivo responses to very intense clicks.

Acoustic Stimulation↗

PubMed1997

Low-frequency suppression of auditory nerve responses to characteristic frequency tones.

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.

Acoustic Stimulation↗

PubMed1997

Basilar-membrane responses to tones at the base of the chinchilla cochlea.

Basilar-membrane responses to single tones were measured, using laser velocimetry, at a site of the chinchilla cochlea located 3.5 mm from its basal end. Responses to low-level (< 10-20 dB SPL) characteristic-frequency (CF) tones (9-10 kHz) grow linearly with stimulus intensity and exhibit gains of 66-76 dB relative to stapes motion. At higher levels, CF responses grow monotonically at compressive rates, with input-output slopes as low as 0.2 dB/dB in the intensity range 40-80 dB. Compressive growth, which is significantly correlated with response sensitivity, is evident even at stimulus levels higher than 100 dB. Responses become rapidly linear as stimulus frequency departs from CF. As a result, at stimulus levels > 80 dB the largest responses are elicited by tones with frequency about 0.4-0.5 octave below CF. For stimulus frequencies well above CF, responses stop decreasing with increasing frequency: A plateau is reached. The compressive growth of responses to tones with frequency near CF is accompanied by intensity-dependent phase shifts. Death abolishes all nonlinearities, reduces sensitivity at CF by as much as 60-81 dB, and causes a relative phase lead at CF.

Acoustic Stimulation↗

PubMed1997

Two-tone distortion on the basilar membrane of the chinchilla cochlea.

Basilar membrane responses to pairs of tones were measured, with the use of a laser velocimeter, in the basal turn of the cochlea in anesthetized chinchillas. Frequency spectra of basilar membrane responses to primary tones with frequencies (f1, f2) close to the characteristic frequency (CF) contain prominent odd-order two-tone distortion products (DPs) at frequencies both higher and lower than CF (such as 2f1-f2, 3f1-2f3, 2f2-f1 and 3f2-2f1). For equal-level primaries with frequencies such that 2f1-f2 equals CF, the magnitude of the 2f1-f2 DP grows with primary level at linear or faster rates at low stimulus levels, but it saturates or decreases slightly at higher levels. For a fixed level of one of the primary tones, the magnitude of the 2f1-f2 DP is a nonmonotonic function of the level of the other primary tone. For low intensities of the variable tone, the 2f1-f2 DP grows at a rate of approximately 2 dB/dB with f1 level and 1 dB/dB with f2 level. DP magnitudes decrease rapidly with increasing primary frequency ratio (f2/f1) at low stimulus levels. For more intense stimuli, DP magnitudes remain constant or decrease slowly over a wide range of frequency ratios until a critical value is reached, at which DP magnitudes fall with slopes as steep as -300 dB/octave. As stimulus level grows, DP phases increasingly lag for large f2/f1 ratios, but exhibit leads for small f2/f1 ratios. Cochlear exposure to an intense tone that produces large sensitivity losses for the primary frequencies (but only small losses for tones with frequency equal to 2f1-f2) causes a substantial decrease in magnitude of the 2f1-f2 DP. This result demonstrates that the 2f1-f2 DP originates at the basilar membrane region with CFs corresponding to the primary frequencies and propagates to the location with CF equal to the DP frequency. 2f1-f2 DPs on the basilar membrane resemble those measured in human psychophysics in most respects. However, the magnitude of basilar membrane DPs does not show the nonmonotonic dependence on f2/f1 ratio evident in DP otoacoustic emissions.

Animals↗

PubMed1992

Basilar membrane responses to two-tone and broadband stimuli.

The responses to sound of mammalian cochlear neurons exhibit many nonlinearities, some of which (such as two-tone rate suppression and intermodulation distortion) are highly frequency specific, being strongly tuned to the characteristic frequency (CF) of the neuron. With the goal of establishing the cochlear origin of these auditory-nerve nonlinearities, mechanical responses to clicks and to pairs of tones were studied in relatively healthy chinchilla cochleae at a basal site of the basilar membrane with CF of 8-10 kHz. Responses were also obtained in cochleae in which hair cell receptor potentials were reduced by systemic furosemide injection. Vibrations were recorded using either the Mössbauer technique or laser Doppler-shift velocimetry. Responses to tone pairs contained intermodulation distortion products whose magnitudes as a function of stimulus frequency and intensity were comparable to those of distortion products in cochlear afferent responses. Responses to CF tones could be selectively suppressed by tones with frequency either higher or lower than CF; in most respects, mechanical two-tone suppression resembled rate suppression in cochlear afferents. Responses to clicks displayed a CF-specific compressive nonlinearity, similar to that present in responses to single tones, which could be profoundly and selectively reduced by furosemide. The present findings firmly support the hypothesis that all CF-specific nonlinearities present in the auditory nerve originate in analogous phenomena of basilar membrane vibration. However, because of their lability, it is almost certain that the mechanical nonlinearities themselves originate in outer hair cells.

Acoustic Stimulation↗

PubMed1992

Two-tone suppression in the basilar membrane of the cochlea: mechanical basis of auditory-nerve rate suppression.

1. The vibratory response to two-tone stimuli was measured in the basilar membrane of the chinchilla cochlea by means of the Mössbauer technique or laser velocimetry. Measurements were made at sites with characteristic frequency (CF, the frequency at which an auditory structure is most sensitive) of 7-10 kHz, located approximately 3.5 mm from the oval window. 2. Two-tone suppression (reduction in the response to one tone due to the presence of another) was demonstrated for CF probe tones and suppressor tones with frequencies both higher and lower than CF, at moderately low stimulus levels, including probe-suppressor combinations for which responses to the suppressor were lower than responses to the probe tone alone. 3. For a fixed suppressor tone, suppression magnitude decreased as a function of increasing probe intensity. 4. The magnitude of suppression increased monotonically with suppressor intensity. 5. The rate of growth of suppression magnitude with suppressor intensity was higher for suppressors in the region below CF than for those in the region above CF. 6. For low-frequency suppressor tones, suppression magnitude varied periodically, attaining one or two maxima within each period of the suppressor tone. 7. Suppression was frequency tuned: for either above-CF or below-CF suppressor tones, suppression magnitude reached a maximum for probe frequencies near CF. 8. Cochlear damage or death diminished or abolished suppression. There was a clear positive correlation between magnitude of suppression and basilar-membrane sensitivity for responses to CF tones. 9. Suppression tended to be accompanied by small phase lags in responses to CF probe tones. 10. Because all of the features of two-tone suppression at the basilar membrane match qualitatively (and, generally, also quantitatively) the features of two-tone rate suppression in auditory-nerve fibers, it is concluded that neural two-tone rate suppression originates in mechanical phenomena at the basilar membrane. 11. Because the lability of mechanical suppression parallels the loss of sensitivity and frequency tuning due to outer hair cell dysfunction, the present findings suggest that mechanical two-tone suppression arises from an interaction between the outer hair cells and the basilar membrane.

Acoustic Stimulation↗

PubMed1992

Strength training via high frequency electrical stimulation.

Twelve males and twelve females received 18 sessions of high frequency (2500 Hz) electrical stimulation of either the biceps brachii or triceps brachii muscles. Each session consisted of ten 10-second contractions separated by 50 seconds of rest. Pre- and post-test measurements included arm flexion and extension strength, endurance, girths and fatfolds. The analysis of variance revealed that there were no significant differences for any of the pre versus post parameters. These findings suggest that electrical stimulation, by itself, is not an adequate training stimulus in normal healthy muscles. The data support the contention that volitional training is required to gain strength.

Adult↗

PubMed1991

Two-tone distortion in the basilar membrane of the cochlea.

When humans listen to pairs of thnes they hear additional tones, or distortion products, that are not present in the stimulus. Two-tone distortion products are also known as combination tones, because their pitches match combinations of the primary frequencies (f1 and f2, f2 greater than f1), such as f2-f1, (n + 1)f1-nf2 and (n + 1)f2-nf1 (n = 1, 2, 3...). Physiological correlates of the perceived distortion products exist in responses of auditory-nerve fibres and inner hair cells and in otoacoustic emissions (sounds generated by the cochlea, recordable at the ear canal). Because the middle ear responds linearly to sound and neural responses to distortion products can be abolished by damage to hair cells at cochlear sites preferentially tuned to the frequencies of the primary tones, it was hypothesized that distortion products are generated at these sites and propagate mechanically along the basilar membrane to the location tuned to the distortion-product frequency. But until now, efforts to confirm this hypothesis have failed. Here we report the use of a new laser-velocimetry technique to demonstrate two-tone distortion in basilar-membrane motion at low and moderate stimulus intensities.

Animals↗

PubMed1991

Application of a commercially-manufactured Doppler-shift laser velocimeter to the measurement of basilar-membrane vibration.

A commercially-available laser Doppler-shift velocimeter has been coupled to a compound microscope equipped with ultra-long-working-distance objectives for the purpose of measuring basilar membrane vibrations in the chinchilla. The animal preparation is nearly identical to that used in our laboratory for similar measurements using the Mössbauer technique. The vibrometer head is mounted on the third tube of the microscope's trinocular head and its laser beam is focused on high-refractive-index glass microbeads (10-30 microns) previously dropped, through the perilymph of scala tympani, on the basilar membrane. For equal sampling times, overall sensitivity of the laser velocimetry system is at least one order of magnitude greater than usually attained using the Mössbauer technique. However, the most important advantage of laser-velocimetry vis-à-vis the Mössbauer technique is its linearity, which permits undistorted recording of signals over a wide velocity range. Thus, for example, we have measured basilar-membrane responses to clicks whose waveforms have dynamic ranges exceeding 60 dB.

Acoustic Stimulation↗

PubMed1991

Furosemide alters organ of corti mechanics: evidence for feedback of outer hair cells upon the basilar membrane.

A widely held hypothesis of mammalian cochlear function is that the mechanical responses to sound of the basilar membrane depend on transduction by the outer hair cells. We have tested this hypothesis by studying the effect upon basilar membrane vibrations (measured by means of either the Mössbauer technique or Doppler-shift laser velocimetry) of systemic injection of furosemide, a loop diuretic that decreases transduction currents in hair cells. Furosemide reversibly altered the responses to tones and clicks of the chinchilla basilar membrane, causing response-magnitude reductions that were largest (up to 61 dB, averaging 25-30 dB) at low stimulus intensities at the characteristic frequency (CF) and small or nonexistent at high intensities and at frequencies far removed from CF. Furosemide also induced response-phase lags that were largest at low stimulus intensities (averaging 77 degrees) and were confined to frequencies close to CF. These results constitute the most definitive demonstration to date that mechanical responses of the basilar membrane are dependent on the normal function of the organ of Corti and strongly implicate the outer hair cells as being responsible for the high sensitivity and frequency selectivity of basilar membrane responses. A corollary of these findings is that sensorineural hearing deficits in humans due to outer hair cell loss reflect pathologically diminished vibrations of the basilar membrane.

Acoustic Stimulation↗

PubMed1990

Middle-ear response in the chinchilla and its relationship to mechanics at the base of the cochlea.

The responses of the malleus and the stapes to sinusoidal acoustic stimulation have been measured in the middle ears of anesthetized chinchillas using the Mössbauer technique. With "intact" bullas (i.e., closed except for venting via capillary tubing), the vibrations of the tip of the malleus reach a maximal peak velocity of about 2 mm/s in responses to 100-dB SPL tones in the frequency range 500-6000 Hz; vibration velocity diminishes toward lower frequencies with a slope of about 6 dB/oct. Opening the bulla widely increases the responses to low-frequency stimuli by as much as 16 dB. At low frequencies, malleus response sensitivity with either open or intact bullas far exceeds all previous measurements in cats and matches or exceeds such measurements in guinea pigs. Whether measured in open or intact bullas, phase-versus-frequency curves closely approximate those predicted from the magnitude-versus-frequency curves by minimum phase theory. The stapes responses are similar to those of the malleus, except that stapes response magnitude is lower, on the average, by 7.5 dB at frequencies below 2 kHz and 10.7 dB at 2 kHz and above. Comparison of the responses of the middle ear with those of the basilar membrane at a site 3.5 mm from the stapes indicates that, at frequencies below 150 Hz, the basilar membrane displacement is proportional to stapes acceleration. At frequencies between 150 and 2000 Hz, basilar membrane displacement is proportional to stapes velocity.

Acoustic Impedance Tests↗

PubMed1990

Electromyography of rapid forearm flexion and extension and aging.

This investigation examined several parameters of agonist- and antagonist-muscle activity and movement time in young and old males during rapid, forearm flexion and extension tasks. Maximal isometric strength of the forearm flexors and extensors and limb-volume measurements were also procured. The subject sample included sixteen males in each of the following groups: 1) thirty to forty year olds, 2) fifty to sixty year olds, and 3) sixty-one to seventy year olds. The averaged, electromyographic patterns (AEMG) of the biceps brachii and triceps brachii muscles were recorded during unloaded and loaded trials of forearm flexion and extension to a predetermined target. Sixteen temporal and ten quantitative parameters were examined. Significant differences between age groups were observed for only the quantitative-parameter accuracy. The conclusions were that an individual's agonist- and antagonist-muscle-activity parameters are maintained into the seventh decade. Flexion and extension strengths decrease progressively with age. Analysis of the limb-volume measures revealed that the oldest group had the greatest amount of fat in each of the segments evaluated.

Adult↗

PubMed1987

Effects of excitatory and non-excitatory suppressor tones on two-tone rate suppression in auditory nerve fibers.

Recordings were obtained from individual auditory nerve fibers in anesthetized chinchillas. Rate versus level functions were obtained for best frequency (BF) tones alone and for simultaneously-gated tone pairs comprising a BF tone and a second tone at a fixed intensity that produced evidence of two-tone rate suppression. Care was taken in selecting a range of suppressor tone levels that included excitatory (i.e., the suppressor tone evoked a rate change by itself) and non-excitatory (i.e., no suppressor tone-evoked rate increase) suppressor tone levels. Addition of a suppressor tone produced a shift of the dynamic range portion of the BF rate versus level function to higher test intensities. A parallel shift of the dynamic range portion of the rate versus level function was associated with a non-excitatory suppressor tone. The shift produced by an excitatory suppressor tone was characterized by a decrease in slope. Results indicated that the magnitude of shift increased monotonically as suppressor tone intensity was raised and that there was a gradual transition from a non-excitatory response to an excitatory response. The rate of shift (i.e., dB of shift per dB change in suppressor tone intensity) did not differ for non-excitatory versus excitatory responses, but was substantially greater for below-BF suppressor tones (1.38 dB/dB) than for above-BF suppressor tones (0.54 dB/dB). The rate of shift did not, however, appear to be related systematically to suppressor tone frequency separation from BF. Above- and below-BF suppression was noted for fibers over the range of best frequencies tested (110 Hz to 16.4 kHz).

Acoustic Stimulation↗

PubMed1987

Timing of spike initiation in cochlear afferents: dependence on site of innervation.

1. The phase of excitation of inner hair cells (IHCs) relative to basilar membrane motion has been estimated as a function of best frequency (BF) (or, equivalently, cochlear location) by recording responses to tones (100-1,000 Hz) from chinchilla cochlear afferent axons at their central exit from the internal auditory meatus. 2. The time of IHC excitation (i.e., the time of chemical transmitter release) was derived from the neural recordings at near-threshold levels by applying a correction for the latency of synaptic processes and the propagation time of action potentials. 3. The phase of basilar membrane motion at the appropriate innervation site was estimated on the basis of previously measured basilar membrane responses at a location close to the basal end of the cochlea and estimates of mechanical travel time from the basal end to the innervation site, derived from the neural latencies to intense rarefaction clicks, as a function of BF. 4. The derived near-threshold excitation of basal IHCs leads basilar membrane displacement toward scala tympani by approximately 40-60 degrees. 5. At BFs corresponding to midcochlear locations (2-6 kHz) there is an abrupt phase transition. The derived excitation for IHCs located at more apical locations (BFs large in relation to stimulus frequency) corresponds approximately to peak velocity of the basilar membrane toward scala vestibuli. 6. Although the derived response phases of apically located IHCs are consistent with intracellular recordings from IHCs, the derived near-threshold response phases of basal IHCs may be inconsistent with intracellular IHC recordings. 7. The foregoing results, based on responses of nearly 1,000 cochlear afferents to tones 100-1,000 Hz at near-threshold stimulus levels, amply confirm our previous conclusions that were based on a smaller sample of responses to very low frequency tones (less than or equal to 100 Hz): there is a spatial transition at midcochlear regions in the mode of excitation of IHCs, which does not seem to simply reflect the macromechanics of the basilar membrane. 8. It has been proposed that both the paradoxical response phases of high-BF afferents and the spatial phase transition arise from an influence of cochlear microphonics on the transmembrane potential of IHCs. The present results, which show that the spatial phase transition occurs for frequencies at least as high as 400 Hz, would appear to make such an electrical influence of outer hair cells on IHCs less likely. An alternative explanation might be that the phase transition has a mechanical basis, perhaps localized to micromechanical events in the subtectorial regio

Acoustic Stimulation↗

PubMed1986

Cochlear microphonics and the initiation of spikes in the auditory nerve: correlation of single-unit data with neural and receptor potentials recorded from the round window.

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 à 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 degrees (but generally less than 45 degrees), depending on frequency. It is shown here that the discrepancy is resolved if certain nonlinear phase changes and overall distortion of the microphonic 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. AP1 is nearly synchronous with the negative-to-positive transition of round window microphonics and with the excitation of fibers innervating apical-to-middle cochlear regions. AP2 is synchronous with the positive-to-negative 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.

Acoustic Stimulation↗

PubMed1986

Basilar membrane mechanics at the base of the chinchilla cochlea. I. Input-output functions, tuning curves, and response phases.

Basilar membrane (BM) velocity was measured at a site 3.5 mm from the basal end of the chinchilla cochlea using the Mössbauer technique. The threshold of the compound action potential recorded at the round window in response to tone bursts was used as an indicator of the physiological state of the cochlea. The BM input-output functions display a compressive nonlinearity for frequencies around the characteristic frequency (CF, 8 to 8.75 kHz), but are linear for frequencies below 7 and above 10.5 kHz. In preparations with little surgical damage, isovelocity tuning curves at 0.1 mm/s are sharply tuned, have Q10's of about 6, minima as low as 13 dB SPL, tip-to-tail ratios (at 1 kHz) of 56 to 76 dB, and high-frequency slopes of about 300 dB/oct. These mechanical responses are as sharply tuned as frequency-threshold curves of chinchilla auditory nerve fibers with corresponding CF. There is a progressive loss of sensitivity of the mechanical response with time for the frequencies around CF, but not for frequencies on the tail of the tuning curve. In some experiments the nonlinearity was maintained for several hours, in spite of a considerable loss of sensitivity of the BM response. High-frequency plateaus were observed in both isovelocity tuning curves and phase-frequency curves.

Action Potentials↗

PubMed1986

Basilar membrane mechanics at the base of the chinchilla cochlea. II. Responses to low-frequency tones and relationship to microphonics and spike initiation in the VIII nerve.

Low-frequency stimuli (40- to 1000-Hz tones) have been used to correlate the motion of the 8-to 9-kHz place of the chinchilla basilar membrane with the cochlear microphonics recorded at the round window and with the responses of auditory nerve fibers with appropriate characteristic frequency. At the lowest stimulus frequencies, maximum displacement of the basilar membrane toward scala tympani occurs in near synchrony with maximum rarefaction at the eardrum and maximum negativity at the round window; at higher frequencies, the mechanical and microphonic response phases progressively lag rarefaction, reaching - 240 deg at 1000 Hz. At most frequencies (40-1000 Hz) near-threshold neural responses, once corrected for neural travel-time and synaptic delays, somewhat lead (by some 40 deg) maximal scala tympani displacement and maximal negativity of the round window microphonics. The variation of sensitivity with frequency is similar for basilar membrane displacement and microphonic responses: Under open-bulla conditions, sensitivity is constant for frequencies between 100 and 1000 Hz; below 100 Hz, sensitivity decreases at rates close to 12 dB/oct toward lower frequencies. Neural response sensitivity matches BM displacement more closely than BM velocity.

Action Potentials↗