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P Dallos

Publications and source records attributed to P Dallos.

At least 73 records · Page 4Linked to original sources
PubMed1989

Neural response to very low-frequency sound in the avian cochlear nucleus.

Recordings were made in the chick cochlear nucleus from neurons that are sensitive to very low frequency sound. The tuning, discharge rate response and phase-locking properties of these units are described in detail. The principal conclusions are: 1. Low frequency (LF) units respond to sound frequencies between 10-800 Hz. Best thresholds average 60 dB SPL, and are occasionally as low as 40 dB SPL. While behavioral thresholds in this frequency range are not available for the domestic chick, these values are in good agreement with the pigeon behavioral audiogram (Kreithen and Quine 1979). 2. About 60% of the unit population displays tuning curves resembling low-pass filter functions with corner frequencies between 50-250 Hz. The remaining units have broad band-pass tuning curves. Best frequencies range from 50-300 Hz. 3. Spontaneous discharge rate was analyzed quantitatively for LF units recorded from nucleus angularis. The distribution of spontaneous rates for LF units is similar to that seen from higher CF units (300-5000 Hz) found in the same nucleus. However, the spontaneous firing of LF units is considerably more regular than that of their higher CF counterparts. 4. Low frequency units with low spontaneous rates (SR's less than 40 spikes/s) show large driven rate increases and usually saturate by discharging once or twice per stimulus cycle. Higher SR units often show no driven rate increases. 5. All LF units show strong phase-locking at all excitatory stimulus frequencies. Vector strengths as high as 0.98 have been observed at moderate sound levels. 6. The preferred phase of discharge (relative to the sound stimulus) increases with stimulus frequency in a nearly linear manner. This is consistent with the LF units being stimulated by a traveling wave. The slope of these phase-frequency relationships provides an estimate of traveling wave delay. These delays average 7.2 ms, longer than those seen for higher CF auditory brainstem units. These observations suggest that the peripheral site of low frequency sensitivity is the very distal region of the basilar papilla, an area whose morphology differs significantly from the rest of the chick basilar papilla. 7. LF units are described whose response to sound is inhibitory at frequencies above 50 Hz.

Acoustic Stimulation↗
PubMed1989

Two-tone suppression in inner hair cell responses.

In an attempt to characterize certain aspects of two-tone suppression (2TS), ac receptor potentials were recorded from mammalian inner hair cells (IHC) in the third turn of the guinea pig cochlea. By comparing magnitude and phase changes occurring during suppression with predictions made on the basis of level-dependent responses to single-tone inputs, it is possible to determine whether 2TS is mimicked by simply attenuating stimulus intensity. Results indicate that the effects of suppression are not simulated by simple input attenuation for low probe levels which produce responses below saturation. In these situations, the suppressor causes a decrease in the magnitude of the ac receptor potential with the largest deviations measured at the characteristic frequency (CF) of the cell. Thus, frequency response functions become broader. Response phase goes through a lag/lead transition at CF, also opposite to the results expected by simply decreasing input to the cell. At higher probe levels, within the saturation region, the magnitude reductions produced during 2TS are largest for stimulus frequencies well below and well above CF. This effect partially reverses the broadening of frequency response functions seen at moderate intensities with possible benefits for the processing of complex stimuli at conversational levels. Although the magnitude data obtained at high probe levels are consistent with the attenuation hypothesis, the companion phase measures did not show the expected lead/lag transition through CF since phase changes were generally lags. Consequently, the high-level suppression data suggest that 2TS may reduce input to the IHC but in a way which is not equivalent to the attenuation of a single-input stimulus.

Acoustic Stimulation↗
PubMed1989

Frequency difference limens in normal and sensorineural hearing impaired chinchillas.

This study assessed normal frequency discrimination ability in the chinchilla and determined how this ability changes as a function of an experimentally induced sensorineural hearing loss. Four chinchillas were trained by the methods of positive reinforcement to report absolute thresholds and frequency difference limens (FDLs). Subjects were then treated with the aminoglycosidic antibiotic amikacin until a 30-dB hearing loss was measured at 10.0 kHz. Absolute and frequency difference thresholds were determined during and after drug treatment. When post-drug thresholds had stabilized, subjects were sacrificed and their cochleas stained, embedded in plastic, microdissected, and viewed with phase contrast microscopy to permit examination of the cochlear tissue. Post-drug data suggest that frequency discrimination at a high frequency is unaffected by a 40- to 45-dB sensorineural hearing loss, considerable hair cell damage, and the resultant disruption of the cochlear micromechanics. The data, in concert with previously published reports, suggest that FDLs may be less affected by a high-frequency sensorineural hearing loss than by a low-frequency sensorineural hearing loss.

Amikacin↗
PubMed1989

Intracellular recordings from supporting cells in the guinea-pig cochlea: AC potentials.

Supporting cells and hair cells from the low-frequency region of the guinea-pig cochlea were studied in vivo using intracellular recording and horseradish peroxidase marking techniques. Response characteristics of the support cells to tone bursts at various sound levels, frequencies, and durations were compared to hair-cell responses and potentials recorded in the organ of Corti fluid spaces. Findings suggest that the fundamental component of the support-cell response accrues from hair-cell-generated currents. This component of the support-cell response probably results from the flow of receptor currents across support-cell membranes through nonspecialized membrane patches, or across nonspecialized membranes and through gap junctions that couple adjacent support cells. Findings suggest a lack of electrotonic coupling between hair cells and neighboring support cells.

Acoustic Stimulation↗
PubMed1989

Nonlinearities in cochlear receptor potentials and their origins.

Using intracellular recording methods in vivo [P. Dallos, J. Neurosci. 5, 1591-1608 (1985)], various nonlinear characteristics of receptor potentials from hair cells located in the low-frequency region of the guinea pig cochlea have been examined. Patterns of saturation for ac and dc response components obtained from Fourier analysis and directly from averaged waveforms are studied. Growth patterns of lower harmonic components are investigated and the interesting nonmonotonic properties of even harmonics noted. The latter are seen in both inner and outer hair cell responses, primarily with stimuli near the cells' best frequency. Fundamental ac and the dc potentials occasionally exhibit nonmonotonic growth. These patterns are studied and their occurrence in inner and outer hair cell responses considered.

Acoustic Stimulation↗
PubMed1987

Positive endocochlear potential: mechanism of production by marginal cells of stria vascularis.

The positive endocochlear potential (EP+) and high K+ concentration of the endolymph in the scala media of the mammalian cochlea are unusual. They have long been assumed to be due to a putative K-pump in the luminal membrane of the marginal cells of the stria vascularis, which were believed to have a negative internal potential. We show that the cell potential is more positive than the EP+, and that the ion pump is conventional Na,K-ATPase, probably in the basolateral membrane. The latter was determined from experiments in which the ionic environment of the strial cells was controlled by perfusion of the perilymphatic space of the cochlea, in the absence of vascular circulation. While the usual EP+ was maintained by normal perfusate, replacement of Na+ by choline resulted in a negative EP, showing that Na,K-ATPase is necessary for the production of EP+. Elimination of K+ as well as Na+ from the perfusate did not change the value of the negative EP, showing that no K-ATPase is involved.

Animals↗
PubMed1986

Neurobiology of cochlear inner and outer hair cells: intracellular recordings.

Recordings were made in the low-frequency region (third and fourth turns) of the guinea pig cochlea from both inner (IHC) and outer (OHC) hair cells. Certain electrical characteristics of these cells that have been described before (P. Dallos (1985) J. Neurosci. 5, 1591-1608) are reviewed. These are resting membrane potentials, response magnitude and saturation, and response phase. A comparison of sensitivity and best frequency is provided for IHCs and OHCs that are located in the same cochlear region. New data are presented for the level-dependence of response phase and for the properties of response asymmetry and the resulting dc component. The effects of intracellular polarizing current upon ac response magnitude are shown for both cell types.

Animals↗
PubMed1986

Intracellular recordings from supporting cells in the organ of Corti.

Horseradish peroxidase marking and intracellular recording techniques were utilized to examine whether the heterogeneity of supporting cell types is reflected in their electrical behavior. The magnitudes of ac and dc response components were compared to their extracellular counterparts. The relationships among these potentials seem to be governed by the cell's location within the organ of Corti.

Animals↗
PubMed1986

Spike activity recorded from the organ of Corti.

During microelectrode passes through the inner hair cell region of the organ of Corti, spike activity is frequently encountered. We have obtained both extracellular and intracellular records from afferent terminals or dendrites. The response characteristics of all-or-none spike trains mimic those recorded from primary auditory axons. EPSPs may be identified, either associated with the spikes or in the absence of a spike. Inferences may be made about the nature of neurotransmitter quantum release from inner hair cells.

Action Potentials↗
PubMed1986

Auditory filter shapes in the chinchilla.

Auditory filter shapes were determined for the chinchilla using the notched-noise technique [R. D. Patterson, J. Acoust. Soc. Am. 59, 640-654 (1976)]. Here, the derivative of the curve relating threshold to masker gap width outlines the shape of the auditory filter. Three chinchillas were trained, using positive reinforcement techniques, to provide forward masked thresholds at 1.0 and 10.0 kHz, at three masker spectrum levels. Unexpectedly, the threshold curves contained inflection points and regions of constant or nonmonotonic changes in threshold, so that the derived filters contained dips in their central passbands. Nonmonotonic variations in threshold may be discerned in human threshold versus notch width functions of previously published studies, suggesting that the two types of data are qualitatively similar. The filters computed from the chinchilla data widened with increasing masker level and were more broadly tuned than those obtained in humans. The physiological response to each frequency component of any stimulus is likely a combination of excitation and suppression. Hence, one cannot predict masked threshold from the acoustic spectra of the maskers used here since they differ from their internal representations. Thus the threshold versus notch width function probably reflects the operation of both an auditory filter and a nonlinearity.

Acoustic Stimulation↗
PubMed1985

Ontogenic changes in cochlear characteristic frequency at a basal turn location as reflected in the summating potential.

In these experiments the development of summating potential (SP) responses in gerbils from neonates to adults was followed. Special recording techniques were used to eliminate maturational effects associated with the middle ear so that developmental changes in cochlear physiology were isolated for study. Results indicate that as development proceeds the frequency that maximally excites the basilar membrane (BM) of the gerbil at a specific mid-basal turn electrode location progresses from low to high, demonstrating a 1.5 octave shift from the onset of the generation of electrical activity until adult-like response are obtained. These findings support the theory proposed by E.W. Rubel (in: Handbook of Sensory Physiology, Vol. IX: Development of Sensory Systems, pp. 135-237. Editor: M. Jacobsen. Springer-Verlag, New York) which explains the observed development of physiological responses measured in the cochlea and higher centers in terms of changing micromechanical transduction properties of the BM.

Aging↗
PubMed1985

Response characteristics of mammalian cochlear hair cells.

Intracellular recordings were made from the low frequency region (third turn) of the guinea pig cochlea. Response characteristics are compared to gross potentials obtained from the organ of Corti fluid space. Inner hair cells (IHCs) possess relatively low (median, -32 mV) initial membrane potentials, whereas that of outer hair cells (OHCs) is higher (median, -53.5 mV). In response to tone burst stimuli, both cell types produce a combination of AC and DC responses. The latter are depolarizing for IHCs but may be of either polarity for OHCs. In terms of their AC responses, IHCs are about 12 dB more sensitive than OHCs. At low sound levels these cells are more linear than high frequency hair cells (Russell, I. J., and P. M. Sellick (1978) J. Physiol. (Lond.) 284: 261-290), judging from the relation between AC and DC response components. At high sound levels pronounced response saturation is seen. The overall tuning properties of the two hair cell types are rather similar, even though IHCs exhibit low frequency velocity dependence, whereas OHCs are displacement sensitive and the cell membrane time constant is larger for IHCs. In order to fit IHC experimental data it is necessary to assume the presence of an underdamped complex pole above the best frequency. The electrical behavior of the OHC does not disqualify it as a conveyor of auditory information to the central nervous system, even though its primary function may be that of a mechanical effector (evidence summarized by Dallos, P. (1985) in Contemporary Sensory Neurobiology, Alan R. Liss, Inc., New York, pp. 207-230).

Animals↗
PubMed1985

Membrane potential and response changes in mammalian cochlear hair cells during intracellular recording.

In the preceding paper (Dallos, P. (1985) J. Neurosci. 5: 1591-1608) some fundamental properties of cochlear inner and outer hair cells were considered. On the basis of intracellular recording from the low frequency region of the guinea pig cochlea, such measures as membrane potentials, the dependence of AC and DC receptor potential magnitude on stimulus level and frequency, and tuning characteristics relative to gross responses were discussed. During prolonged recording various changes in membrane and receptor potentials were observed. In the present paper the relationship between these variations is described and evaluated in the context of a simple hair cell model.

Animals↗
PubMed1984

Ontogenetic changes in frequency mapping of a mammalian ear.

Cochlear microphonic iso-response functions reported here suggest an explanation of frequency-dependent changes in hearing sensitivity during early development. The work is a direct demonstration of developmental changes in the spatial frequency map of the mammalian hearing organ. Intracochlear recordings from the midbasal turn in a series of age-graded gerbils reveal a progressive increase in best frequency, spanning approximately two octaves, from the time of onset of function until adultlike responses are seen. It is, therefore, suggested that ontogenetic changes in the cellular structure of the organ of Corti contribute to an age-dependent shift in micromechanical response.

Aging↗
PubMed1984

Summating potential (SP) tuning curves.

Two methods were used to extract frequency specific information from the gross d.c. cochlear potential, the summating potential (SP). The first approach was to derive SP tuning curves using a two-tone simultaneous masking procedure; the second to obtain SP iso-response functions. The influence of various parameter changes on the configuration of these functions was also investigated. While SP tuning curves measured using the two-tone paradigm have higher Q10 dB values than SP iso-response functions in the base of the cochlea, the latter have the advantage of avoiding contamination by various nonlinear phenomena which are inherent in the simultaneous tone-on-tone masking procedure. Since SP tuning curves are similar to those for basilar membrane motion (Sellick, P.M., Patuzzi, R. and Johnstone, B.M. (1982): J. Acoust. Soc. Am. 72, 131-141) and the whole nerve action potential (AP) (Cheatham, M.A. and Dallos, P. (1979): J. Acoust. Soc. Am. 65, S13), nearly the same degree of tuning may be reflected at these peripheral recording locations.

Action Potentials↗
PubMed1984

Some electrical circuit properties of the organ of Corti. II. Analysis including reactive elements.

The simplified network model of the organ of Corti-hair cell complex that was studied in previous publications (Dallos, P. (1983): In: Hearing - Physiological Bases and Biophysics, pp. 32-37, editors: R. Klinke and R. Hartmann; Dallos, P. (1983): Hearing Res. 12, 89-119) is extended to include the capacitive reactances of hair cell 12, 89-119) is extended to include the capacitive reactances of hair cell membranes. With the assumption that the circuit is parametrically excited by resistance changes of the apical hair cell membrane, intracellular responses for outer (eO) and inner (eI) hair cells and the organ of Corti potential (eOC) are computed for the linear case. In order that frequency-dependent effects be primarily determined by the network properties of the system, the eO/eOC and eI/eOC ratios are considered. The amplitude and phase dependence of these computed functions is compared to corresponding experimental results from the third turn of the guinea pig's cochlea. The eO/eOC function is predicted to be a simple low-pass filter whose cutoff frequency (1250 Hz) is determined by the parallel resistance-capacitance circuit of the cell's baso-lateral membrane. This circuit prediction is in excellent agreement with the data. The eI/eOC function is again derived as a low-pass filter. The cutoff frequency is obtained as 472 Hz, which corresponds to an RC membrane time constant of 0.34 ms. Experimental data are widely divergent from this predicted pattern. In order to bring the theoretical and experimental results in agreement, two steps are necessary. First, a differentiation (i.e., multiplication by j omega) needs to be included in the input to inner hair cells to account for their velocity dependence [4,10]. Second, an underdamped complex pole, located above the cell's best frequency must be introduced. The velocity dependence and the resonance represented by the underdamped pole-pair indicate that the electrical response pattern of inner hair cells is more complex than that of outer hair cells.

Cell Membrane↗