Biomedical subjects

Mark E Chertoff

Publications and source records attributed to Mark E Chertoff.

9 recordsLinked to original sources

PubMed2006

Columella footplate motion and the cochlear microphonic potential in the embryo and hatchling chicken.

A piezoelectric (PZE) vibrator was used to mechanically drive the columella footplate and stimulate the cochlea of chicken embryos and hatchlings. Our objectives were to characterize the motion of the PZE driver and determine the relationship between columella footplate motion (displacement/ velocity) and the cochlear microphonic recorded from the recessus scala tympani (CMrst). At each frequency, displacement of the PZE driver probe tip was linearly related to the applied voltage over a wide range of attenuation levels (-60 to -20 dBre:50 Vp-p). The mean displacement across frequencies (100-4000 Hz) was 0.221+/-0.042 micromp-p for a constant applied voltage level of -20 dBre:50 Vp-p. Displacement was within 1.5 dB of the mean for this stimulus level at all frequencies except for 4000 Hz, where it was approximately 3 dB higher (p < 0.01). CMrst amplitudes in hatchlings were larger than amplitudes in embryos (p=0.003). For a given frequency, CM was linearly related to footplate displacement and velocity at both ages. The transform ratio of CMrst/A (CM amplitude/displacement) increased at approximately 6 dB/octave at frequencies between 100 and 1000 Hz in hatchlings suggesting that cochlear impedance (Zc) was resistive at these frequencies. In a large fraction of the embryos, Zc exhibited reactive behavior.

Animals↗

PubMed2005

Predicting severity of cochlear hair cell damage in adult chickens using DPOAE input-output functions.

Distortion product otoacoustic emissions (DPOAE) were recorded from the ear canal of aged broiler chickens which have been shown to present with age-related cochlear degeneration [Hear. Res. 166 (2002) 82]. We describe the relationship between the shape of the DPOAE input-output (I/O) function and the type of hair cell damage present at and between the cochlear frequency places of the DPOAE primary tones (f1 and f2). The mid stimulus level compressive growth of the mean DPOAE I/O functions is reduced in a graded fashion relative to the severity of hair cell damage. However, individual DPOAE I/O functions within most hair cell damage groups show large variability from this characteristic. Various least squares regression models were used to predict hair cell density from indices derived from the DPOAE I/O function (area, threshold and slope). The results showed that no simple linear relationship exists between hair cell density and the DPOAE I/O function indices. Multivariate binary logistic regression used DPOAE I/O function indices to predict membership in hair cell damage groups. The logistic model revealed that DPOAE threshold can be used to predict the occurrence of severe/total hair cell damage with good specificity though poor sensitivity.

Aging↗

PubMed2004

Cochlear hysteresis: observation with low-frequency modulated distortion product otoacoustic emissions.

Low-frequency modulation of distortion product otoacoustic emissions (DPOAEs) can be used to estimate a nonlinear transducer function (fTr) of the cochlea. From gerbils, DPOAEs were measured while presenting a high-level bias tone. Within one period of the bias tone, the magnitudes of the cubic difference tone (CDT, 2f1 - f2) demonstrated two similar modulation patterns (MPs) each resembled the absolute value of the third derivative of the fTr. The center peaks of the MPs occurred at positive sound pressures for rising in bias pressure or loading of the cochlear transducer, and more negative pressures while decreasing bias amplitude or unloading. The corresponding fTr revealed a sigmoid-shaped hysteresis loop with counterclockwise traversal. Physiologic indices that characterized the double MP varied with primary level. A Boltzmann-function-based model with negative damping as a feedback component was proposed. The model was able to replicate the experimental results. Model parameters that fit to the CDT data indicated higher transducer gain and more prominent feedback role at lower primary levels. Both physiologic indices and model parameters suggest that the cochlear transducer dynamically changes its gain with input signal level and the nonlinear mechanism is a time-dependent feedback process.

Acoustic Stimulation↗

PubMed2004

Constructing a cochlear transducer function from the summating potential using a low-frequency bias tone.

A new method is developed to construct a cochlear transducer function using modulation of the summating potential (SP), a dc component of the electrical response of the cochlea to a sinusoid. It is mathematically shown that the magnitude of the SP is determined by the even-order terms of the power series representing a nonlinear function. The relationship between the SP magnitudes and the second derivative of the transducer function was determined by using a low-frequency bias tone to position a high-frequency probe tone at different places along the cochlear transducer function. Two probe tones (6 kHz and 12 kHz) ranging from 70 to 90 dB SPL and a 25-Hz bias tone at 130 dB SPL were simultaneously presented. Electric responses from the cochlea were recorded by an electrode placed at the round window to obtain the SP magnitudes. The experimental results from eight animals demonstrated that the SP magnitudes as a function of bias levels are essentially proportional to the second derivative of a sigmoidal Boltzmann function. This suggests that the low-frequency modulated SP amplitude can be used to construct a cochlear transducer function.

Acoustic Stimulation↗

PubMed2004

Analytic treatment of the compound action potential: estimating the summed post-stimulus time histogram and unit response.

The convolution of an equation representing a summed post-stimulus time histogram computed across auditory nerve fibers [P(t)] with an equation representing a single-unit wave form [U(t)], resulted in an analytic expression for the compound action potential (CAP). The solution was fit to CAPs recorded to low and high frequency stimuli at various signal levels. The correlation between the CAP and the analytic expression was generally greater than 0.90. At high levels the width of P(t) was broader for low frequency stimuli than for high frequency signals, but delays were comparable. This indicates that at high signal levels there is an overlap in the population of auditory nerve fibers contributing to the CAP for both low and high frequency stimuli but low frequencies include contributions from more apical regions. At low signal levels the width of P(t) decreased for most frequencies and delays increased. The frequency of oscillation of U(t) was largest for high frequency stimuli and decreased for low frequency stimuli. The decay of U(t) was largest at 8 kHz and smallest at 1 kHz. These results indicate that the hair cell or neural mechanisms involved in the generation of action potentials may differ along the cochlear partition.

Acoustic Stimulation↗

PubMed2003

Influence of hearing sensitivity on mechano-electric transduction.

This study examined the relation between the extent of permanent hearing loss and the change in a third-order polynomial transducer function (PTF) representing mechano-electric transduction (MET). Mongolian gerbils were exposed to noise for 1 to 128 h. A control group received no exposure. The cochlear microphonic (CM) was recorded from a round-window electrode and stapes velocity was recorded with a laser Doppler vibrometer in response to Gaussian noise. A nonlinear systems identification procedure provided the frequency-domain coefficients of the PTF and their associated coherence functions. In the control group, the PTF in the high frequencies was dominated by linear and cubic terms. In noise-exposed animals, the magnitude of these terms decreased with increasing threshold, suggesting a progressive decrease in the receptor currents through basal hair cells. Moreover, the linear coherence increased and the cubic coherence decreased, indicating that MET in the cochlear base became linear. In the low frequencies, noise exposure altered the group delay of the CM, demonstrating a redistribution of hair-cell currents. The low-frequency PTF was characterized by an increase in the contribution in the quadratic term. With increasing threshold, the slope of the PTF decreased and the saturation for positive CM was eliminated.

Action Potentials↗

PubMed2002

The influence of inner hair cell loss on the instantaneous frequency of the cochlear microphonic.

The cochlear microphonic (CM) is produced by a change in standing currents during the motion of the cochlear partition. The motion of the partition and associated hair cell transduction processes are nonlinear and are reflected in the variation of the instantaneous frequency (IF) of the CM. Although the CM is dominated from receptor currents from outer hair cells (OHCs), receptor currents from inner hair cells (IHCs) may contribute to the fluctuation in the IF. In this paper we examine the influence of IHCs on the variation of the IF of the CM. A 75 mg/kg intraperitoneal (i.p.) dose of carboplatin reduced the IHC population by approximately 40%. The reduction in IHCs did not substantially affect the amplitude of the CM. The amplitude of the IF, however, was reduced at high signal levels (90 and 100 dB peak SPL). A phenomenological model of the CM indicated that the contribution of IHC receptor currents to the IF was small and that changes in OHC transducer characteristics may have a greater impact on the IF.

Acoustic Stimulation↗

PubMed2002

Deriving a cochlear transducer function from low-frequency modulation of distortion product otoacoustic emissions.

In this paper, a new method is introduced to derive a cochlear transducer function from measuring distortion product otoacoustic emissions (DPOAEs). It is shown that the cubic difference tone (CDT, 2f1-f2) is produced from the odd-order terms of a power series that approximates a nonlinear function characterizing cochlear transduction. Exploring the underlying mathematical formulation, it is found that the CDT is proportional to the third derivative of the transduction function when the primary levels are sufficiently small. DPOAEs were measured from nine gerbils in response to two-tone signals biased by a low-frequency tone with different amplitudes. The CDT magnitude was obtained at the peak regions of the bias tone. The results of the experiment demonstrated that the shape of the CDT magnitudes as a function of bias levels was similar to the absolute value of the third derivative of a sigmoidal function. A second-order Boltzmann function was derived from curve fitting the CDT data with an equation that represents the third derivative of the Boltzmann function. Both the CDT-bias function and the derived nonlinear transducer function showed effects of primary levels. The results of the study indicate that the low-frequency modulated DPOAEs can be used to estimate the cochlear transducer function.

Acoustic Stimulation↗

PubMed2002

Characterizing cochlear mechano-electric transduction with a nonlinear system identification technique: the influence of the middle ear.

Previously a third-order polynomial equation characterizing mechano-electric transduction was obtained from a nonlinear system identification procedure applied to an ear canal acoustic signal and cochlear microphonic (CM/AC). In this paper, we examine the influence of the linearity and frequency response of the intervening middle ear on the nonlinearity, frequency response, and coherence of the third-order polynomial model of mechano-electric transduction (MET). Ear canal sound pressure (AC), cochlear microphonics (CM), and stapes velocity (SV) were simultaneously recorded from Mongolian gerbils. Linear and nonlinear transfer and coherence functions relating stapes velocity to the acoustic signal (SV/AC), CM to the acoustic signal (CM/AC), and CM to the stapes velocity (CM/SV) were computed. The results showed that SV/AC was linear while CM/AC and CM/SV were not, indicating that the nonlinearity of CM/AC was not due to nonlinearity of the middle ear. The frequency response of the linear term of CM/AC was similar to that of ST/AC but differed from that of CM/SV while the cubic term of CM/AC was similar to that of CM/SV. This indicates that the frequency dependence of CM/AC was due to both the middle ear and frequency dependence of the inner ear. Finally the fit of the polynomial model of MET without the middle ear (CM/SV) did not improve from the fit including the middle ear (CM/AC). A cochlear model of the CM indicated that the lack of improvement was due to the limitations of a third-order polynomial equation characterizing the hair cell transducer function.

Animals↗