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J J Zwislocki

Publications and source records attributed to J J Zwislocki.

At least 19 recordsLinked to original sources
PubMed1992

Ionic coupling among cells in the organ of Corti.

Gap junctions have been demonstrated morphologically among the supporting cells of the mammalian organ of Corti but, in contradistinction to reptiles, evidence for their existence between the supporting cells and hair cells is equivocal. The literature is ambiguous with respect to electrical coupling and dye coupling among the supporting cells, and no coupling of either kind has been demonstrated for the hair cells. We found strong coupling of both kinds among the supporting cells in the cochleas of live Mongolian gerbils and a less stable coupling between the supporting cells and the outer hair cells. The electrical coupling was established by recording alternating receptor potentials in the hair cells and following their decrement in the population of Hensen's cells; the dye coupling, by injecting Lucifer yellow electrophoretically into the hair cells or the supporting cells and investigating its spread to the neighboring cells. The electrical recordings were made by means of microelectrodes filled with either 1.5 or 3 M KCl or 1 M LiCl with 6% Lucifer yellow, the latter used for dye injection. The electrode resistances ranged from about 20 to 60 M omega in the first instance, and from about 50 to 110 M omega, in the second. The electrodes were inserted into the organ of Corti through scala media according to the method of Dallos, Santos-Sacchi and Flock (1982) modified by us. The alternating potential in Hensen's cells was usually larger than in the outer tunnel of Corti and remained practically constant up to the outer margin of the Hensen's-cell population. Its phase was the same as in the outer hair cells. When the dye was injected into a Hensen's cell, it always spread to neighboring Hensen's cells and often to Deiter's cells. Dye injected into outer hair cells (identified according to anatomical and physiological criteria) also spread to Deiter's and Hensen's cells and, usually, to other outer hair cells. Stained cells were identified in surface preparations and, on two occasions, in serial sections from plastic embedded cochleas.

Animals↗
PubMed1991

What is the cochlear place code for pitch?

The advent of cochlear implants has increased the clinical interest in the cochlear code for pitch. It is widely believed that pitch is determined by the location of the excitation maximum in the cochlea. However, direct recordings from cochlear hair cells indicate that, for a given sound frequency, the location changes appreciably with sound intensity, whereas the corresponding pitch remains approximately constant. Correlated with this constancy is a surprising constancy of the location of the high-frequency cutoff of cochlear excitation.

Acoustics↗
PubMed1989

Tectorial membrane. II: Stiffness measurements in vivo.

The tectorial membrane is assumed to play a crucial role in the stimulation of the cochlear hair cells and was thought for decades to serve as a stiff anchor for the tips of the hair-cell stereocilia, particularly those belonging to the OHCs. Yet, its stiffness has never been measured under conditions approximating its normal environment in live animals. We have developed a method for doing this. The tectorial membrane is approached through the lateral wall of scala media. The bony cochlear capsule is removed along scala media over somewhat less than 1/4 turn, and the underlying spiral ligament and stria vascularis are carefully reflected. With the help of a three axial hydraulic manipulator, a flexible micropipette filled with isotonic KCl is inserted into the tectorial membrane at one of two different angles and moved either transversally, away from the basilar membrane, or radially, toward or away from the modiolus. This causes the tectorial membrane to be deformed and the micropipette to bend. The micropipette stiffness is calibrated on an instrument of a new kind, so as to convert the bend into force. The calibration allows us to determine the point stiffness of the tectorial membrane from the amount of micropipette bend. The stiffness of the tectorial membrane per unit length has been calculated from the point stiffness with the help of the deformation pattern. Transversal and radial stiffness magnitudes have been determined in the second cochlear turn in Mongolian gerbils. Both are smaller by almost an order of magnitude than the corresponding aggregate stiffness of the OHC stereocilia. As a consequence, the tectorial membrane cannot act as a stiff anchor for the stereocilia but only as a mass load, except at relatively low sound frequencies where mass effects are negligible. This means that the classical model of shear motion between the tectorial membrane and the reticular lamina must be replaced.

Animals↗
PubMed1989

Intensity discrimination determined with two paradigms in normal and hearing-impaired subjects.

The literature on auditory intensity jnd's is ambiguous with respect to the relationship between the jnd's measured with gated and continuous pedestals and with respect to changes in this relationship in the presence of loudness recruitment accompanying cochlear pathology. In an attempt to clarify these issues and to lay a foundation for systematic investigations of the dependence on the jnd's on loudness functions, the jnd's for pure tones with gated- and continuous-pedestal paradigms of two groups of subjects, one with normal hearing and one with hearing loss of cochlear origin, were measured. The experiments were performed at 0.5, 2, and 6 kHz, and at a wide range of sensation levels (SLs) by means of an adaptive two-alternative, forced-choice (2IFC) procedure. The jnd's obtained with the continuous-pedestal method were smaller than those obtained with the gated-pedestal method for both groups of subjects. They also had smaller intersubject standard deviations. When jnd's of the two groups were compared on the basis of equal SLs, the group with hearing loss showed smaller jnd values than the group with normal hearing for both pedestal paradigms. When the comparisons were made on the basis of equal sound-pressure levels (SPLs), both groups showed similar values for moderate and high SPLs. At relatively low SPLs, the group with hearing loss tended to have somewhat higher values.

Acoustic Stimulation↗
PubMed1988

Tectorial membrane. I: Static mechanical properties in vivo.

Although the tectorial membrane in the mammalian cochlea plays a crucial role in hair-cell stimulation, its mechanical properties have never been investigated under conditions approximating those under which it normally functions. For this reason, we performed such investigations in live Mongolian gerbils. Access to the tectorial membrane was gained through the lateral wall in the second cochlear turn. As far as possible, sodium ions were kept away from the tectorial membrane by avoiding injury to Reissner's membrane, relieving the perilymphatic pressure, and rinsing the scala media with an isotonic KCl solution. The tectorial membrane was manipulated with a flexible micropipette in three, approximately orthogonal, directions. Under these conditions the membrane was found to be highly compliant and resilient, and to have a relatively high tensile strength. Its viscosity was low. Some of these attributes were altered by sodium ions, dyes, or death.

Animals↗
PubMed1986

Analysis of cochlear mechanics.

A large number of experimental results on basilar-membrane vibration, cochlear microphonics, hair-cell receptor potentials, and spike rates in auditory nerve afferents are brought together to arrive at a comprehensive concept of cochlear mechanics, including hair-cell stimulation. Beginning with basilar-membrane tuning curves, we note that some of their most detailed determinations reveal a small notch and a secondary maximum above the best frequency in addition to sharp tuning. These features tend to become more prominent as the sharpness of tuning decreases. They cannot be accounted for on the assumption that the cochlear partition represents a simple second-order system consisting of distributed, elastically suspended mass. A higher order system is required. The cross-sectional structure of the partition suggests a fifth-order system made up of two sets of distributed resonators, one consisting essentially of the distributed mass of the organ of Corti supported by the stiffness of the basilar membrane, the other of the tectorial-membrane mass and its elastic attachment to the spiral limbus. The stiff stereocilia of the outer hair cells appear to serve as the main elastic coupling between the two resonator sets. Interaction of the two resonator sets is brought into evidence particularly clearly by weakening the coupling between the tectorial membrane and the organ of Corti. This can be achieved by manipulating the tectorial membrane with a microelectrode without affecting the endolymphatic potential. The partial decoupling leads to a transformation of a unimodal CM transfer function into a bimodal one. Except for the stiffness of the tectorial-membrane attachment to the limbus, the masses and stiffnesses involved in the two coupled resonator systems can be estimated independently on the basis of available measurements. Their application to an approximate computer model of the cochlea produced a cochlear frequency map consistent with experimental findings. The computer model, whose elements are in one-to-one correspondence with the gross elements of the cochlear partition, reproduces approximately the fundamental amplitude and phase characteristics of the measured basilar-membrane vibration. In particular, it reproduces the notch and the secondary maximum located above the best frequency. Our current computer model is linear and does not reproduce the known cochlear distortion products. Nevertheless, variation of those of its stiffness and resistance elements that correspond to the hair-cell stereocilia has allowed us to reproduce typical changes in basilar-membrane vibration, which accompany changes in sound intensity or cochlear deterioration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Are nonlinearities observed in firing rates of auditory-nerve afferents reflections of a nonlinear coupling between the tectorial membrane and the organ of Corti?

Shear motion between the reticular lamina and the tectorial membrane at the location of the inner hair cells, studied on a network model of the cochlea with a nonlinear coupling between the two structures, exhibits the same type of nonlinearities as seen in the firing rates of auditory-nerve afferents. They include wave form distortions, phase changes and nonmonotonic dependence of the output amplitude on the cochlear input amplitude.

Animals↗
PubMed1986

On the relations of intensity jnd's to loudness and neural noise.

It is shown experimentally that, in contradiction of the fundamental concept of Fechner's law, the intensity jnd for auditory sinusoidal signals follows loudness, rather than its derivative with respect to sound intensity. The evidence is obtained by comparing the jnd's of a population with normal hearing to those of a population with hearing loss accompanied by loudness recruitment. Although the recruitment increases the slope of the loudness function, the jnd's of both populations were found to be practically equal when the loudness were equal. The phenomenon is accounted for mathematically by assuming that psychophysically relevant neural noise depends not only on the magnitude of loudness, but also on its derivative with respect to sound intensity. A related derivation accounts for the near miss to Weber's law.

Adult↗
PubMed1979

Tectorial membrane: a possible effect on frequency analysis in the cochlea.

Mathematical analysis and computer and network simulations of the cochlea show that, given appropriate values of specific physical constants, radial shear motion between the tectorial membrane and the reticular lamina may provide the sharpening of frequency analysis observed in cochlear nerve fibers in comparison with the mechanical amplitude distribution on the basilar membrane. According to the analysis, the sharpening occurs through an interaction of the longitudinal mechanical propagation constant of the tectorial membrane with the wavelength on the basilar membrane.

Basilar Membrane↗
PubMed1978

Low-frequency neural and cochlear-microphonic tuning curves in the gerbil.

Average tuning curves of single auditory-nerve fibers are compared with average cochlear-microphonic (CM) tuning curves corrected for electrical filtering of the cochlea. Both the neural and CM data were obtained from Mongolian gerbils (Meriones unguiculatus) with the same acoustic system and similar corrections for middle-ear effects. Under these conditions the CM tuning in the second and third cochlear turns is similar to the tuning of fibers whose characteristic frequencies (CFs) correspond to the CM best frequencies (2.5 and 0.5 dHz). Thus, little sharpening seems to take place for low CF fibers. CM tuning at the most apical electrode position is sharper than expected for frequencies below the best frequency--a result that may be due to the shunting effect of the helicotrema at low frequencies- Previous modeling results have confirmed that apical basilar-membrane tuning may be appreciable affected by the mechanical impedance of the helicotrema. This helicotrema effect may account for the nearly symmetrical shapes of neural tuning curves of low-CF fibers.

Action Potentials↗
PubMed1975

Phase opposition between inner and outer hair cells and auditory sound analysis.

Recordings of single-unit responses in the auditory nerve of normal and kanamycin-treated Mongolian gerbils indicate that inner and outer hair cells of the cochlea interact in phase opposition. After kanamycin treatment, the firing rate in some fibers is increased during the basilar membrane motion toward scala vestibuli, in others, during its motion towards scala tympani. Because of statistical correlation with anatomical changes and characteristic time patterns, the first response polarity is associated with inner hair cells, the second, with outer hair cells. It is shown that normal responses can be reconstructed from the two kinds of responses seen after kanamycin treatment. The phase opposition between inner and outer hair cells, in connection with the expected effect of spiral fibers, provides an explanation for neural sharpening of mechanical filter action in the cochlea.

Acoustic Stimulation↗
PubMed1973

Velocity and displacement responses in auditory-nerve fibers.

With the help of nonsiniusoidal acoustic stimuli, it is demonstrated that most fibers of the auditory nerve respond to both displacement and velocity of the basilar membrane. Except at very high stimulus levels, motion and displacement toward scala tympani produce excitation; motion and displacement toward scala vestibuli produce inhibition. The displacement and velocity responses interact. When both are excitatory or inhibitory, they reinforce each other; when they are of opposite nature, a partial cancellation occurs. The presence of both displacement and velocity responses in the single fibers suggests that outer and inner hair cells of the cochlea interact.

Acoustic Stimulation↗