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Biomedical subjects

D O Kim

Publications and source records attributed to D O Kim.

At least 55 records · Page 3Linked to original sources
PubMed1991

Spatial response profiles of posteroventral cochlear nucleus neurons and auditory-nerve fibers in unanesthetized decerebrate cats: response to pure tones.

Encoding of 1- and 5-kHz pure tones by auditory-nerve (AN) fibers and choppers of the posteroventral cochlear nucleus (PVCN) was investigated. Neuronal responses were analyzed as the discharge rate, rate change, and the mean and standard deviation (or sigma) of spike counts. The major findings are: (1) Sideband inhibitory areas were observed in spatial profiles of rate changes of PVCN choppers whereas they were absent in those of AN fibers; (2) spatial profiles of rate changes and mean discharge rates of PVCN choppers were sharper than those of high spontaneous-rate (HSR) AN fibers and were comparable to those of low and medium SR (LMSR) AN fibers for 1 kHz at 50 and 70 dB SPL re: 20 microPa; (3) to 5 kHz, 30 dB SPL, PVCN choppers were strongly driven comparable to HSR AN fibers whereas LMSR AN fibers were weakly driven (implying higher thresholds); (4) PVCN choppers exhibited higher maximum discharge rates (300-600 spikes/s) than either LMSR AN fibers (200-250 spikes/s) or HSR AN fibers (150-250 spikes/s); (5) mean-to-sigma ratios of PVCN choppers, particularly at 70 dB SPL, were much higher than those of LMSR or HSR AN fibers; (6) rate-change profiles of LMSR AN fibers were distinct from those of HSR AN fibers, more conspicuously for 1 kHz than for 5 kHz; (7) the neural response profiles to 5 kHz were sharper than those to 1 kHz; and (8) 45% of PVCN choppers in the present study exhibited SR greater than 20 spikes/s whereas only 11%-12% of AVCN choppers in previous studies of anesthetized cats exhibited the same SR, which may represent an effect of anesthesia. The observations support a hypothesis that the transformation of the discharge-rate signal from AN fibers to PVCN choppers leads to an amplification of the mean discharge-rate signal with an increase in the signal-to-noise ratio. The observations suggest that PVCN choppers can encode pure-tone frequency in a spatial profile more accurately than HSR or LMSR AN fibers. The present data on AN and PVCN spatial profiles should be valuable to CN modeling studies by providing the input to the CN and the output of a class of physiologically characterized CN neurons for an identical set of stimuli.

Animals↗
PubMed1991

Simulations of cochlear nucleus neural circuitry: excitatory-inhibitory response-area types I-IV.

Several circuitry schemes have been explored among model stellate and fusiform cochlear nucleus neurons in an effort to reproduce excitatory-inhibitory response-area (EIRA scheme) types I-IV. Single cell models incorporated known nonlinear membrane properties and spike-discharge characteristics, as described in previous modeling and intracellular recording. In addition, a unique method of implementing dendritic electrotonic distance processing was developed that provides greater computational efficiency, but with results similar to compartmental models. As an initial simple case, results were examined for a kHz pure tone. Auditory nerve (AN) population responses across characteristic frequencies from 200 Hz to 50 kHz based on actual single unit recordings were incorporated into the model as input. The findings and conclusions are (1) relatively simple inhibitory connections among stellate and fusiform cells, all of which receive AN excitatory inputs, can account for the salient features of EIRA-scheme types I-IV; (2) both types III and IV may be obtained using fusiform cells with small adjustments in the anatomical connections; (3) if stellate cells laterally inhibit their own neighbors, they can create inhibitory sidebands, but may have difficulty avoiding multiple sidebands; (4) in the model, type II cells are not responsive to broadband noise but rather to pure tones, and the reason for this was partly because the type II cells were inhibited by other CN units, and partly because the simulated AN fiber response to broadband noise was near their threshold; and (5) the type IV complex response areas may actually arise not necessarily because of elaborate circuitry, but as a result of a complex AN fiber population profile at high stimulus levels in conjunction with the type II inhibitory input to the type IV cells.

Acoustic Stimulation↗
PubMed1991

Otoacoustic emissions in normal and hearing-impaired children and normal adults.

Although distortion-product otoacoustic emissions (DPOEs) have been studied in adults recently, there is little information regarding them in young children. DPOEs and click-evoked otoacoustic emissions (CEOEs) were measured from a same group of normal and hearing-impaired children (age 4 through 10 years) and normal adults (age 22 through 29 years). Measurements of DPOEs in 13 children's ears with normal hearing showed higher levels of emissions in the 700- to 1400-Hz and 5.7-kHz regions relative to the data obtained in 10 normal adult ears. The 22 ears of children with sensorineural hearing loss demonstrated agreement between pure-tone audiograms and "DPOE audiograms." Measurements of CEOEs revealed that the average level of emission in 15 normal-hearing children's ears was slightly lower than that previously obtained in newborns, but slightly higher than that of adults. In children, the CEOE spectral components in the 4- to 6-kHz region were lower than in newborns, but higher than in adults. These results support the view that the DPOEs and CEOEs comprise a valuable tool in assessment of cochlear function in subjects of all ages.

Acoustic Stimulation↗
PubMed1990

Distortion product otoacoustic emissions in normal and impaired adult ears.

Distortion product otoacoustic emissions (DPOEs) were recorded in a group of normally hearing subjects (29 ears) and a group of subjects whose conditions were diagnosed as sensorineural hearing loss (23 ears) to study any correlation that might exist between DPOE characteristics and hearing impairment of different configurations. Three different DPOE paradigms have been used to investigate the influence of different test parameters on the DPOE data for normal and hearing-impaired ears. All normally hearing ears demonstrated detectable DPOEs, provided that the primary tone level was above a certain value. Hearing-impaired ears produced substantially reduced DPOEs compared with normally hearing subjects when the primary frequencies f1 and f2 corresponded to the region of hearing loss. Our data also suggested that, in general, more than one f2/f1 ratio is needed to examine any particular frequency region. The DPOEs provide frequency-specific information about cochlear function, which after further development, may form a basis for a noninvasive, objective method of evaluating cochlear function.

Acoustics↗
PubMed1990

Responses of DCN-PVCN neurons and auditory nerve fibers in unanesthetized decerebrate cats to AM and pure tones: analysis with autocorrelation/power-spectrum.

We investigated amplitude-modulated (AM) tone encoding behavior of dorsal and posteroventral cochlear-nucleus (DCN and PVCN) neurons and auditory nerve (AN) fibers in decerebrate unanesthetized cats. Some of the modulation transfer functions (MTFs) were narrowly-tuned band-pass functions; these included responses at moderate and high stimulus levels of DCN pause/build-type-III neurons and the following types of DCN and PVCN chopper neurons: chop-S and/or chop-type-I/III. Other MTFs were broad low-pass or complex functions. Chop-T neurons of the DCN and PVCN tended to exhibit low-pass or flat MTFs. The band-pass MTF neurons exhibited intrinsic oscillations (IOs) in responses to AM or pure tones. The IOs, which were detected in autocorrelation functions and power spectra, were closely correlated (r = 0.863) with the best envelope frequency (BEF). All of the AN fibers showed broad low-pass MTFs with some showing a rudimentary peak in the MTF. The MTFs of DCN-PVCN neurons and AN fibers showed, respectively: (1) BEFs ranging 50-500 Hz, and 400-1300 Hz; (2) upper cut-off frequencies ranging 200-1200 Hz, and 1600-3200 Hz. At stimulus levels of 60-85 dB SPL, maximum modulation gains were as high as 12 dB for DCN-PVCN neurons but were limited to below about 0 dB for AN fibers. The median dynamic ranges of DCN and PVCN neurons (51 and 42 dB, respectively) were substantially wider than those of the low and high spontaneous rate AN fibers (30 and 31 dB, respectively). The observation of higher modulation gain, wider dynamic range, and more narrowly-tuned MTF of DCN-PVCN neurons than AN fibers supports the concept that the capabilities to encode dynamic signals are enhanced in DCN-PVCN neurons compared with AN fibers.

Acoustic Stimulation↗
PubMed1990

A population study of auditory-nerve fibers in unanesthetized decerebrate cats: response to pure tones.

Population responses of single auditory-nerve (AN) fibers to 1-kHz pure tones were investigated in unanesthetized decerebrate cats. Driven rate (spikes/s), Fourier component amplitude (spikes/s), and d'e = (driven rate)/(standard deviation) were examined. These results extend the presently available information. First, the AN population responses, previously observed only in anesthetized animals, are now observed in unanesthetized animals. The anesthetized and unanesthetized animal responses are qualitatively similar. Second, a detectability measure d'e was applied, à la signal detection theory, to populations of AN fibers. A previously unknown behavior of the low-spontaneous-rate (SR) (less than 15 spikes/s) fibers was observed: the d'e increased to large values at moderate and high stimulus levels, giving rise to a large, sharply tuned peak in the d'e-place profile, even when the driven rate was saturated. This behavior was absent in the high-SR (greater than 15 spikes/s) fibers. This observation suggests that the d'e of the low-SR fibers is the best code for stimulus intensity among the different response measures examined, and that the d'e-place profile may be a more precise spatial code for stimulus frequency than the commonly considered rate-place code.

Animals↗
PubMed1986

Active and nonlinear cochlear biomechanics and the role of outer-hair-cell subsystem in the mammalian auditory system.

An increasing amount of support is accumulating for the hypothesis that the outer hair cells (OHC) of a mammalian cochlea give rise to an enhanced sensitivity and markedly sharp tuning of the mechanical response of the cochlear partition. The enhancing and sharpening effects of the OHCs are postulated to arise from a bidirectional transduction mechanism whereby not only a mechanical signal applied to the hair bundle is (forward) transduced into electrophysiological signals, but also an electrophysiological signal applied to the hair cell is (reverse) transduced into generation of mechanical forces and related displacements. This paper will review experimental evidence for the hypothesis and attempt to integrate results of various experimental and theoretical studies into a coherent framework.

Animals↗
PubMed1986

A model for active elements in cochlear biomechanics.

A linear, mathematical model of cochlear biomechanics is presented in this paper. In this model, active elements are essential for simulating the high sensitivity and sharp tuning characteristic of the mammalian cochlea. The active elements are intended to represent the motile action of outer hair cells; they are postulated to be mechanical force generators that are powered by electrochemical energy of the cochlear endolymph, controlled by the bending of outer hair cell stereocilia, and bidirectionally coupled to cochlear partition mechanics. The active elements are spatially distributed and function collectively as a cochlear amplifier. Excessive gain in the cochlear amplifier causes spontaneous oscillations and thereby generates spontaneous otoacoustic emissions.

Biomechanical Phenomena↗
PubMed1984

Spontaneous otoacoustic emissions in chinchilla ear canals: correlation with histopathology and suppression by external tones.

Two cases of spontaneous otoacoustic emissions (SOAEs) have been found among a sample of 28 chinchilla ears after noise exposure, and no cases of SOAEs have been found among 28 unexposed ears. Further observations of the characteristics of SOAEs recorded in the ear canals of two chinchillas after noise exposure are described. These signals were tonal, robust, and could be suppressed by presenting external tones to the ear. Histopathological evaluation of the cochlea of emitting ears revealed discrete basal-turn lesions near the positions corresponding to the frequencies of the emissions. Behavioral threshold shifts measured in one animal after noise exposure and acoustic intermodulation distortion product behavior in the other both suggest a region of increased vibratory response of the cochlear partition near the location of the SOAE. Results from these emitting ears support a hypothesis that a punctate loss of the organ of Corti (OC) may facilitate the occurrence of an SOAE. We further hypothesize that the following conditions are both necessary and sufficient for an SOAE to occur: (1) functional disruption of a normally present biomechanical control mechanism in a region of the OC; (2) presence of functionally active OC (especially outer hair cells) adjacent to the region. The observations from ears possessing SOAEs provide strong, though indirect support for active and nonlinear models in interpreting cochlear biomechanical phenomena.

Acoustic Stimulation↗
PubMed1983

An active cochlear model showing sharp tuning and high sensitivity.

Recent in vivo measurements of cochlear-partition motion indicate very high sensitivity and sharp mechanical tuning similar to the tuning of single cochlear nerve fibers. Our experience with mathematical models of the cochlea leads us to believe that this type of mechanical response requires the presence of active elements in the cochlea. We have developed an active cochlear model which incorporates negative damping components; this model produces partition displacement in good agreement with many of the mechanical and neural tuning characteristics which have been observed in vivo by other researchers. We suggest that the negative damping components of our model may represent an active mechanical behavior of the outer hair cells, functioning in the electromechanical environment of the normal cochlea.

Animals↗
PubMed1983

Response of cochlear nerve fibers to brief acoustic stimuli: role of discharge-history effects.

The probability that a cochlear nerve fiber spike discharge occurs during a time interval delta t depends on both the acoustic stimulus and on aftereffects from earlier spike discharges. We have examined the influence of discharge-history on post-stimulus time (PST) histogram responses to acoustic click and tone-burst stimuli. Discharge-history effects were found to include the modification of observed interpeak times of PST responses to clicks, a loss of distinct peaks in the click response of high characteristic frequency (CF greater than 5 kHz) fibers, and changes in the ratio of initial to steady-state response portions of tone-burst responses. The method used to separate discharge-history from stimulus-related factors is based on a model developed in Gaumond et al. [J. Neurophysiol. 48, 856-873 (1982)]. The results are in general agreement with those obtained by the method of Peter Gray [Biophys. J. 7, 759-777 (1967)], which discards from consideration those portions of the response record not preceded by a silent interval of 20 or 25 ms or more. Our method requires more assumptions about the spike train, but produces less variable results by utilizing more of the spike train data.

Acoustic Stimulation↗
PubMed1982

Cochlear microphonic evidence for mechanical propagation of distortion products (f2 - f1) and (2f1 - f2).

The present cochlear microphonic (CM) study was undertaken to help resolve a conflict in the literature regarding cochlear nonlinear properties. The CM studies of Dallos and his coworkers have concluded that "(up to 70-80 dB SPL [re 20 mu Pa]), all orders of distortion components...do not seem to be accompanied by traveling waves of their own" (Dallos, P. (1973): The Auditory Periphery: Biophysics and Physiology. Academic Press, New York). However, studies of spatial distributions of cochlear nerve fiber responses, acoustic distortion products in the ear canal, and related modeling studies of Kim et al. (Kim, D.O. and Molnar, C.E. (1975): in: The Nervous System, Vol. 3: Human Communication and Its Disorders. Editor: D.B. Tower. Raven Press, New York; Kim, D.O., Molnar, C.E. and Matthews, J.W. (1980): J. Acoust. Soc. Am. 67, 1704-1721) have led to conclusions to the contrary. In the present study, CM data were obtained from the second and third turns of the chinchilla cochlea using fluid-filled glass micropipettes in scala media and nichrome wire electrodes in scala vestibuli and scala tympani. We sought responses containing predominant distortion products (f2 - f1) and (2f1 - f2) by fixing a distortion frequency (fD) near the characteristic frequency (CF) of the recording site and varying the stimulus frequencies f1 and f2 and SPLs (with L1 = L2). By subsequently varying the distortion frequency around the CF, e.g., fixing f1 well above the CF and varying f2, we measured the tuning characteristics of the distortion products (f2 - f1) and (2f1 - f2). Tuning characteristics of single-tone responses were measured by applying single-tone stimuli of various frequencies with a constant SPL at the eardrum. We have observed, with SPLs as low as 25 dB, that these distortion products in CM display tuning similar to the single-tone response which is consistent with above neural results. From these tuning similarities, we conclude that our CM data reflect the presence of mechanically propagated distortion products at low SPLs, in agreement with the above studies by Kim et al. Validity of our results is supported by the sensitivity and sharp tuning of our CM data and, in the case of the scala media recordings, by the presence of a normal d.c. endolymphatic potential. Plausible explanations for the opposing conclusions of previous studies of Dallos et al. and the present study are discussed.

Acoustic Stimulation↗
PubMed1982

Efferent neural control of cochlear mechanics? Olivocochlear bundle stimulation affects cochlear biomechanical nonlinearity.

We confirm the report of Mountain (Mountain, D.C. (1980): Science 210, 77-72) that stimulating the crossed olivocochlear bundle (COCB) can change the magnitude of the distortion product (f2-f1) in the ear-canal sound pressure. Our results are extended to include (2f1-f2) as well as (f2-f1) from anesthetized chinchillas with both middle-ear muscles sectioned. In contrast to Mountain's report, the polarity of the change can be either positive, negative or absent, depending on the choice of two-tone stimulus frequencies. The influence of two-tone stimulus level is also complex, but we have not yet seen the polarity of the COCB effect change with stimulus level. The magnitude and polarity of the change in (2f1-f2) are not simply related to those for (f2-f1). The effect of COCB stimulation is abolished when scala tympani is perfused with artificial perilymph containing 10(-5) M d-tubocurarine. These results demonstrate that the COCB effect is postsynaptic, probably mediated by outer hair cells. We suggest that the normal cochlea contains an active biomechanical mechanism which reduces the damping of the cochlear-partition motion and is modulated by activating the efferents. It is thus possible that the central nervous system may be able to control the dynamics of the motion of the cochlear partition.

Acoustic Stimulation↗
PubMed1982

The behavior of acoustic distortion products in the ear canals of chinchillas with normal or damaged ears.

Acoustic intermodulation distortion products were measured in 15 ear canals of chinchillas with normal or damaged ears. Pretreatment results showed that when two primary tones at frequencies f1 and f2, f1 less than f2, were presented at levels from 30 to 90 dB SPL, acoustic distortion products at 2f1-f2 and 2f2-f1 were 30 to 50 dB below primary-tone levels. Noise exposures that caused temporary or permanent hearing loss produced corresponding temporary or permanent reductions in distortion-product levels. Mechanical damage to the cochlea or middle ear reduced the distortion-product levels to below the noise floor of the measurement system. Comparisons of distortion-product level with behaviorally measured threshold shift and cochlear histopathology suggest that, in the absence of conductive impairment, the level of 2f1-f2 or 2f2-f1 can be used as a sensitive indicator of hearing sensitivity and the condition of the cochlea.

Animals↗
PubMed1982

Effects of altering organ of Corti on cochlear distortion products f2 - f1 and 2f1 - f2.

1. Single cochlear nerve fiber recordings from unexposed chinchillas show spatial distributions of amplitude and phase of the distortion products f2 - f1 and 2f1 - f2 similar to those previously reported for the cat (35, 37, 42). 2. Damaging the organ of Corti in the region corresponding to the frequencies of a two-tone stimulus substantially reduces the amplitude of these distortion products at their characteristic places. 3. The distortion products 2f - f1 and 2f1 - f2 thus appear to be generated in the organ of Corti in the region of the primary-frequency places. 4. The neural responses suggest that the distortion products are propagated in the motion of the cochlear partition like externally applied stimulus tones at the distortion frequencies wih a similar spatial distribution of distortion product amplitude and phase. Models of the cochlea that assume nonlinear cochlear-partition dynamics can account for the similarity by demonstrating that distortion products generated by cochlear-partition nonlinearity can propagate apicalward in the motion of the cochlear partition. 5. Models of the cochlea using a linear-system model for cochlear partition motion, in cascade with a nonlinear transduction stage and a subsequent sharp filter, are inadequate to account for present observations, unless two currently implausible assumptions are made: a) stimulus tones near 4 kHz must propagate in normal cochleas at least as far apically as the 300-Hz place with sufficient amplitude to generate f2 - f1 there, and b) damage to the organ of Corti must interfere with this propagation of 4-kHz stimulus tones to the 300-Hz place. 6. Distortion generation in the cochlea is sensitive to delicate alterations of the organ of Corti. Short moderate-intensity exposures to sound can reversibly reduce the amplitudes of the distortion products f2 - f1 and 2f1 - f2 seen in responses from cochlear nerve fibers with characteristic frequencies (CF) near the distortion frequencies. Since such exposures do ot produce permanent structural changes visible under light microscopy, it seems most reasonable to believe that subtle changes in the organ of Corti (most likely in the hair cells themselves) in the region most responsive to f1 and f2 reduce the generation of mechanically present distortion products.

Acoustic Stimulation↗
PubMed1980

Cochlear mechanics: implications of electrophysiological and acoustical observations.

Implications of the spatial distribution of distortion products (2f1--f2) and (f2--f1) observed from populations of cochlear nerve fibers for cochlear mechanics are reviewed (the terms f1 and f2 represent the primary stimulus frequencies; f1 < f2). Characteristics of the distortion products (2f1--f2) and (f2--f1) in the ear-canal sound pressure of the cat and the chinchilla are investigated. Physiological origin of the acoustic distortion product (2f1--f2) is supported by demonstrations of the vulnerability of the distortion product to anoxia, to overstimulation and to cyanide perfusion of the cochlea. Observations are presented describing the dependence of levels of acoustic distortion products (2f1--f2) and (f2--f1): (1) on primary levels; (2) on f2 with iso-f1; and (3) on f1 and f2 with iso-(2f1--f2). Observations and interpretations are discussed in support of the conclusions: (1) that the distortion product (2f1--f2) in the ear-canal sound pressure observed in our studies is not generated in the experimental apparatus, in the eardrum, or in the middle ear but in the primary-frequency region of the cochlea; (2) that the distortion-product generation requires normal physiological processes in the cochlear sensory apparatus but not the neural activity; and (3) that the distortion-product is mechanically propagated from the generation region in the cochlea toward the distortion-frequency place and toward the stapes, through the middle ear, and into the ear canal involving gross motions of the cochlear partition and the middle-ear ossicles. It is now inevitable that we accept the notion that, in a normal ear, manifestations of significant nonlinear behavior are present in the mechanical response of the middle ear and the cochlea at most of the physiologically normal sound pressure levels.

Acoustic Stimulation↗