Biomedical subjects

D O Kim

Publications and source records attributed to D O Kim.

At least 19 recordsLinked to original sources

PubMed2002

Organization of olivocochlear neurons in the cat studied with the retrograde tracer cholera toxin-B.

We employed cholera toxin-B (CTB), an efficient retrograde tracer, to examine olivocochlear (OC) neurons in the cat. Our primary goals were (1). to determine whether the cat has two types of lateral OC (LOC) neurons as is found in certain rodents and (2). to document the morphology, number, and caudorostral distribution of OC neurons, bilaterally. Adult cats received injections of CTB through the round window of the left cochlea, and, after 3-6 days, the brains were sectioned transversely and CTB was revealed immunocytochemically in every section. In three cats, OC neurons were mapped, counted differentially according to cell group, and the numbers of each plotted bilaterally from caudal to rostral. In one cat, measurements were made on labeled LOC and medial OC (MOC) neurons. The results indicate that LOC neurons can be divided into two groups based on their proximity to the lateral superior olive (LSO): a more populous group of small neurons that have intimate contact with the LSO, designated marginal-LOC neurons, and a less populous, morphologically heterogeneous group, lying more distantly from the LSO, designated para-LOC neurons. Para-LOC neurons lying dorsal and rostral to LSO were significantly larger than marginal-LOC. We hypothesize that the cat marginal-LOC neurons and most probably the larger para-LOC neurons correspond to rodent intrinsic and shell LOC neurons, respectively, which have focal versus diffuse projections beneath the inner hair cells. Concerning MOC neurons, we confirm and extend previous observations on the clustering of these neurons near the rostral tip of the medial superior olivary nucleus and also show that MOC neurons differ in size according to cell group. Finally, we compare the present counts of OC neurons (mean total 1607, consisting of 1058 LOC neurons and 549 MOC neurons innervating one cochlea) and their proportional distribution ipsilaterally and contralaterally with those reported previously. Our estimate of the number of LOC neurons is somewhat higher than those previously obtained either by retrograde labeling with horseradish peroxidase or by counting unmyelinated axons in the olivocochlear bundle. In contrast, our estimate of the number of MOC neurons is very similar to those previously reported.

Animals↗

PubMed2001

Adaptation of distortion product otoacoustic emission in humans.

Previous studies of animals observed a phenomenon of adaptation of distortion product otoacoustic emission (DPOAE) and found that the phenomenon was mediated to a large extent by the medial olivocochlear (MOC) reflex. The present study investigated DPOAE adaptation in humans. The following stimuli were used: f2/f1 = 1.2; f2 = 2, 4, or 5.65 kHz; L2 = 50-65 dB SPL re 20 microPa rms, L1 - L2 = 0-15 dB, where L1 and L2 represent levels of the f1 and f2 tones, respectively; duration of two-tone burst = 5.5 s; interburst gap = 20 or 30 s; number of repetitions = 40 or 64. We analyzed the 2f1 - f2 DPOAE as a function of time using a method of heterodyne envelope detection. The subjects were 20 humans aged from 15 to 54 years (median = 21 years) with normal hearing. We observed that (1) humans exhibited DPOAE adaptation phenomenon; (2) the time course of DPOAE level was characterized by a 2-exponential function; (3) distributions of the fast and slow time constants were well separated with their median values being 69 ms and 1.51 s, respectively; (4) distributions of the magnitudes of the fast and slow adaptation components were largely overlapped with their median values being 0.65 and 0.40 dB, respectively; and (5) the combined magnitude of the adaptation ranged from 0.4 to 3.0 dB with a median of 1.10 dB. To our knowledge, the present study is the first published article to describe adaptation of DPOAE in humans. These results should help advance the basic knowledge of human cochlear mechanics operating under the control of the MOC feedback system and contribute to the development of practical applications such as identifying people at high risk of acoustical injury and a clinical test of the functional status of the MOC system.

Adaptation, Physiological↗

PubMed2001

Connections between the dorsal raphe nucleus and a hindbrain region consisting of the cochlear nucleus and neighboring structures.

Previous studies have shown that neurons in the raphe nuclei respond to acoustic stimuli. The present study investigated connections between the dorsal raphe nucleus (DRN) and a hindbrain region consisting of the cochlear nucleus (CN) and neighboring structures. A mixture of one or more tracers (cholera toxin B, biotinylated dextran amine (BDA), and 3H-leucine) was injected into the cat DRN. Retrograde-labeling results are presented whereby a new structure, to be called the juxta-acoustico-floccular fascicle (JAFF), is identified. The JAFF is surrounded by the CN, flocculus, lateral cerebellar nucleus, lateral vestibular nucleus, and restiform body. The JAFF is closely associated with the infracerebellar nucleus (ICN). Labeled neurons projecting to the DRN were concentrated in the JAFF, embedded among axons. Less numerous labeled neurons were in the ICN and CN. Anterograde-labeling results are presented showing fibers labeled with BDA or with BDA and 3H-leucine in the CN, cochlear nerve and vestibular nerve, indicating that the DRN projects to these structures. The ascending and descending connections between the DRN and the above hindbrain region may mediate a reflex that may alter the sensitivity of the auditory system in response to biologically salient (e.g. threatening or attractive) stimuli.

Animals↗

PubMed2000

Projection of the marginal shell of the anteroventral cochlear nucleus to olivocochlear neurons in the cat.

The marginal shell of the anteroventral cochlear nucleus is anatomically and physiologically different from its central core. Previous studies suggest that neurons in the marginal shell are well suited to encode the intensity of acoustic stimuli. To investigate the projections of the marginal shell, a focal injection (<100 nl) of a mixture of biotinylated dextran amine (BDA) and (3)H-leucine was made into the marginal shell of the cat combined with injection of cholera toxin subunit-B (CTB) into the cochleas. Following a 7-day survival, the cats were perfused. Axons and swellings labeled with BDA and olivocochlear neurons labeled with CTB were immunocytochemically stained black and brown, respectively. (3)H-leucine labels were visualized by autoradiography. Labeled neural structures were examined via light microscopy. We found that swellings labeled with BDA, sometimes doubly labeled with BDA and (3)H-leucine, were in close apposition with dendrites and/or somata of olivocochlear neurons identified with CTB labeling. Double labeling with BDA and (3)H-leucine signifies that the label was anterogradely transported. The results support the conclusion that the anteroventral cochlear nucleus projects to medial olivocochlear neurons bilaterally and to lateral olivocochlear neurons ipsilaterally. Furthermore, the results are consistent with the interpretation that the marginal shell provides a source of the above-mentioned projections. Together with information in the literature, the present anatomical results support a hypothesis that the marginal shell provides information about stimulus intensity as a part of a reflex (or feedback gain control) system comprising the cochlea, cochlear neurons, cochlear nucleus, medial olivocochlear neurons, and cochlear outer hair cells.

Animals↗

PubMed2000

Virtual anatomy and movement of lower extremities using virtual reality modeling language.

In medical imaging, the use of three-dimensional image is increasing for both educational and diagnostic purposes. With the advent of techniques for browsing a three-dimensional object, it became possible to display three-dimensional images on a personal computer via the Internet. This report describes the construction of a three-dimensional virtual model of human lower extremities that was linked with the data acquired from gait analysis in order to perform three-dimensional gait analysis.

Anatomy, Cross-Sectional↗

PubMed2000

Purkinje cell degeneration and control mice: responses of single units in the dorsal cochlear nucleus and the acoustic startle response.

The cartwheel cell is the most numerous inhibitory interneuron of the dorsal cochlear nucleus (DCN). It is expected to be an important determinant of DCN function. To assess the contribution of the cartwheel cell, we examined the discharge characteristics of DCN neurons and behavioral measures in the Purkinje cell degeneration (pcd) mice, which lack cartwheel cells, and compared them to those of the control mice. Distortion product otoacoustic emissions and auditory brainstem-evoked response thresholds were similar between the two groups. Extracellularly recorded DCN single units in ketamine/xylazine-anesthetized mice were classified according to post-stimulus time histogram (PSTH) and excitatory-inhibitory response area (EI-area) schemes. PSTHs recorded in mouse DCN included chopper, pauser/buildup, onset, inhibited and nondescript types. EI-areas recorded included Types I, II, III, I/III, IV and V. There were no significant differences in the proportions of various unit types between the pcd and control mice. The pcd units had slightly lower thresholds to characteristic frequency tones; however, they had spontaneous rates, thresholds to noise, and maximum driven rates to noise that were similar to those of the control units. Pcd mice had smaller startle amplitudes, but startle latency, prepulse inhibition/augmentation and facilitation by a background tone were comparable between the two groups. From these results, we conclude that DCN function in response to relatively simple acoustic stimuli is minimally affected by the absence of the cartwheel cells. Future studies employing more complex and/or multimodal stimuli should help assess the role of the cartwheel cells.

Acoustic Stimulation↗

PubMed1999

Distortion product otoacoustic emissions in the CBA/J mouse model of presbycusis.

CBA mice do not exhibit age-related loss of auditory sensitivity or cochlear pathology until relatively late in life. Therefore, this strain is believed to be an excellent animal model for the examination of the effects of age on the cochlea. To evaluate the effects of age on outer hair cell function, 2f1-f2 distortion product otoacoustic emissions (DPOAEs) were measured for f2 between 8 and 16 kHz in CBA/J mice between 1 and 25 months of age. CBA mice exhibited mild age-related changes in DPOAE level and detection threshold at 17 months of age, and changes of 20-40 dB by 25 months of age. The DPOAE level decreased and detection threshold increased with age in a frequency-dependent manner, starting at high frequencies and eventually extending to low frequencies. The range of frequencies in which notches were observed in the DPOAE input/output (I/O) functions extended toward lower frequencies by 17 months of age. Notches were absent in the I/O functions of 25-month-old mice. The present results for a frequency range of 8-16 kHz suggest that age has modest effects on outer hair cell function in CBA mice.

Aging↗

PubMed1999

Adaptation of 2f1-2f2 distortion product otoacoustic emission in young-adult and old CBA and C57 mice.

The phenomenon of efferent-mediated adaptation of 2f1-f2 distortion product otoacoustic emission (DPOAE) was investigated in two strains (CBA/JNia and C57BL/6JNia) of mice of various ages using stimuli presented monaurally or binaurally. The present study demonstrated the existence of the DPOAE adaptation phenomenon in mice analogous to that previously reported in cats. The present data were fitted with one- or two-exponential functions. With a one-exponential fit in 2-month old mice, the adaptation magnitude ranged from 0 to 4 dB with the average value of 0.5 to 1.6 dB and the average time constant was 0.5 to 2.3 s. With a two-exponential fit, the shorter time constant was 0.3 to 1.7 s. The adaptation magnitude and time constant were similar between the monaural and binaural stimulations. We observed that there was a statistically significant decrease of adaptation magnitude in older CBA mice with age-related hearing loss when compared with young adult mice. The results from the young adult mice should be useful in future studies, e.g., a study of developmental changes in post-natal mice, or changes accompanying an alteration in the central auditory system arising from any etiology. We suggest that this phenomenon can be used as a tool for advancing basic knowledge of the auditory system and for assessing an impairment of the olivocochlear system, e.g., in aging.

Acoustic Stimulation↗

PubMed1999

Responses of neurons to click-pairs as simulated echoes: auditory nerve to auditory cortex.

When two identical sounds are presented from different locations with a short interval between them, the perception is of a single sound source at the location of the leading sound. This "precedence effect" is an important behavioral phenomenon whose neural basis is being increasingly studied. For this report, neural responses were recorded to paired clicks with varying interstimulus intervals, from several structures of the ascending auditory system in unanesthetized animals. The structures tested were the auditory nerve, anteroventral cochlear nucleus, superior olivary complex, inferior colliculus, and primary auditory cortex. The main finding is a progressive increase in the duration of the suppressive effect of the leading sound (the conditioner) on the response to the lagging sound (the probe). The first major increase occurred between the lower brainstem and inferior colliculus, and the second between the inferior colliculus and auditory cortex. In neurons from the auditory nerve, cochlear nucleus, and superior olivary complex, 50% recovery of the response to the probe occurred, on average, for conditioner and probe intervals of approximately 2 ms. In the inferior colliculus, 50% recovery occurred at an average separation of approximately 7 ms, and in the auditory cortex at approximately 20 ms. Despite these increases in average recovery times, some neurons in every structure showed large responses to the probe within the time window for precedence (approximately 1-4 ms for clicks). This indicates that during the period of the precedence effect, some information about echoes is retained. At the other extreme, for some cortical neurons the conditioner suppressed the probe response for intervals of up to 300 ms. This is in accord with behavioral results that show dominance of the leading sound for an extended period beyond that of the precedence effect. Other transformations as information ascended included an increased variety in the shapes of the recovery functions in structures subsequent to the nerve, and neurons "tuned" to particular conditioner-probe intervals in the auditory cortex. These latter are reminiscent of neurons tuned to echo delay in bats, and may contribute to the perception of the size of the acoustic space.

Acoustic Stimulation↗

PubMed1998

Responses of anteroventral cochlear nucleus neurons of the unanesthetized decerebrate cat to click pairs as simulated echoes.

To elucidate the contribution of the anteroventral cochlear nucleus (AVCN) to 'echo' processing, this study documents the responses of AVCN neurons to simulated echoes and compares them to those of auditory nerve (AN) fibers. Single unit discharges were recorded from 121 units in the AVCN of 21 unanesthetized decerebrate cats in response to click pairs with inter-click intervals ranging from 1 to 32 ms between 45 and 105 dB SPL re 20 microPa. Units were classified according to the post-stimulus time histogram (PSTH) and excitatory-inhibitory response area (EI-area) schemes. Based on their spontaneous rates (SR), units were subdivided into low- ( < 20 spikes/s) and high- ( > 20 spikes/s) SR groups. A majority of the units exhibited second-click responses whose recovery time courses were similar to those of AN fibers. These units included primary-like, chopper and onset units in the PSTH scheme and Types I, I/III and III units in the EI-area scheme. A minority of the units exhibited responses that were distinct from those of AN fibers, in that they had second-click response recovery times that were either markedly reduced or prolonged. This group of units included those with primary-like, chopper and onset PSTHs and Type I/III and III EI-areas. No significant difference was found in the second-click response among various PSTH or EI-area types. High-SR AVCN units exhibited a decrease in the second-click response with increasing level. In contrast, low-SR AVCN units showed little level-dependent change in the second-click responses. This SR-based difference was similar to that previously found among AN fibers. The present results suggest that, although a majority of AVCN units exhibit similar time courses of second-click response recovery to those of AN fibers, there do exist mechanisms in the cochlear nucleus that can substantially alter this representation. Furthermore, the difference between the second-click response recovery functions of low- and high-SR AVCN units and the consistency of this finding between AVCN and AN suggest that SR represents an important dimension for signal representation in the AVCN neurons.

Acoustic Stimulation↗

PubMed1997

A new method of measuring distortion product otoacoustic emissions using multiple tone pairs: study of human adults.

OBJECTIVE: To increase the speed of a distortion product otoacoustic emissions (DPOE) test of cochlear function by employing a new multiple-tone-pair method and to validate the method. DESIGN: We used a new method of employing multiple tone pairs in measuring DPOEs proposed by Zurek and Rabinowitz and implemented in a modified Grason-Stadler Model GSI-60. We investigated the applicability of the multiple-pair method by comparing the 2f1-f2 DPOEs obtained with a 3-pair method with the conventional 1-pair results in human adults; f1 and f2 represent two frequencies of each tone pair, f1 < f2, f2/f1 = 1.2. We used two sets of 3-pair stimuli: 1) f2 at 1.5, 3, and 6 kHz; and 2) f2 at 2, 4, and 8 kHz. The 1-pair stimuli had f2 at each of the above six frequencies. The primary tone levels were L1 = 65 and L2 = 50 dB SPL re 20 microPa. RESULTS: We obtained DPOEs from 98 ears with normal hearing and 94 ears with sensorineural hearing loss in 103 human adults. We found: 1) that the DPOE levels obtained with the 3-pair method were strongly correlated with those of the 1-pair method, with correlation coefficients of 0.83 to 0.96; 2) that the mean DPOE level versus frequency functions for the normal ears were similar between the 3-pair and 1-pair methods; a 2-way analysis of variance indicated no significant difference between the two methods; 3) that the mean difference between DPOE levels obtained with the 3-pair and 1-pair methods was small (less than 1.3 dB in 11 of the 12 conditions examined, i.e., six frequencies each for normal ears and hearing-impaired ears) although the differences were significant in 6 of the 12 conditions as determined by the paired t-test; and 4) that the DPOE test performances of distinguishing normal from impaired ears were similar between the 3-pair and 1-pair tests; areas under the receiver operating characteristic curves were not significantly different between the two tests for four of the six frequencies tested as determined by a statistical procedure of Hanley and McNeil; for the remaining two frequencies where the differences were significant, each of the two tests was better than the other at one frequency. CONCLUSIONS: The 3-pair DPOE method yielded results generally in good agreement with those of the conventional 1-pair DPOE method. To our knowledge, this is the first systematic study of a multiple-pair DPOE method. Because a 3-pair method can be conducted approximately two to three times as fast as a 1-pair method, the former is advantageous, particularly for an auditory screening test.

Adolescent↗

PubMed1997

Marginal shell of the anteroventral cochlear nucleus: single-unit response properties in the unanesthetized decerebrate cat.

The marginal shell of the anteroventral cochlear nucleus (AVCN) is anatomically different from its central core. We investigated 38 single units in the shells of 10 cats and contrasted them with 62 single units in the cores of 15 cats. The sites of all shell units were localized with the use of reconstructed electrode tracks. The shell units were divided into acoustically well-driven (68%) and weakly/not-driven (32%) subgroups. The shell units mostly exhibited low spontaneous rates (SRs). Among the well-driven shell units, a large majority (68%) exhibited wide dynamic ranges (> or = 50 dB) to tones, noise, or both, with some ranges as wide as 89 dB. In contrast, a large majority (80%) of the core units exhibited narrow dynamic ranges (< 50 dB) to tones and noise. The poststimulus time histograms (PSTHs) of the well-driven shell units included pause-build (29%), onset (24%), and unusual (33%) types, whereas those of the core units included mainly primary-like (47%) and chopper (29%) types. The excitatory-inhibitory areas (EIAs) of the well-driven shell units included types I/III (47%), III (22%), IV (13%), and II (9%), whereas those of the core units included mainly types III (52%) and I/III (32%). On the basis of Fisher's exact tests, we conclude that the shell and core neural groups of the AVCN are significantly different regarding all of the following physiological characteristics: SR, maximum driven rate, threshold and dynamic range to tones and noise, frequency response area, PSTH type, latency, and EIA type. Wide dynamic ranges of the well-driven shell units suggest that they may play a role in encoding absolute intensity of acoustic stimulus.

Acoustic Stimulation↗

PubMed1997

The effect of diphenyl-dimethyl-dicarboxylate on cyclosporine-A blood level in kidney transplants with chronic hepatitis.

An adequate blood level of cyclosporine-A (CsA) is essential to keep graft function in kidney transplants. Due to a narrow therapeutic index and highly variable pharmacokinetic properties associated with CsA, drug interactions may have a significant impact on the immunosuppressive efficacy or toxicity of CsA. Numerous drug interactions of potential clinical significance involving CsA have been reported. Dephenyl-dimethyl-dicarboxylate (PMC), a hepatotonic drug, is a substance derived from the synthesis of Schizandrae fructus elements. We have experienced two cases of drug interaction between CsA and PMC in kidney transplants with chronic hepatitis. In both cases, CsA troughs decreased markedly to a subtherapeutic level following administration of PMC. We, therefore, suggest that PMC could decrease the CsA trough level and thus a close monitoring of the CsA trough level is necessary during a PMC therapy.

Chronic Disease↗

PubMed1996

Marginal shell of the anteroventral cochlear nucleus: intensity coding in single units of the unanesthetized, decerebrate cat.

Single units were recorded in the marginal shell (38 units in 10 cats) and central core (62 units in 15 cats) of the anteroventral cochlear nucleus (AVCN) in unanesthetized decerebrate cats. The recording sites of the shell units were verified in reconstructed electrode tracks, and those of the core units were verified for 18 units and based on the recording depth for 44 units. There was a substantial presence of strongly driven units in the AVCN shell exhibiting non-saturating rate-level functions to pure tone, noise or both with dynamic ranges as wide as 89 dB. This finding supports a hypothesis that the AVCN shell may play a role in encoding acoustic stimulus intensity. The AVCN shell and core populations were different as follows. The shell population had more units which had wide dynamic ranges, low spontaneous rates (SRs) or were acoustically weakly or not driven than the core population. These differences were statistically significant (P < 0.001, Fisher's exact test).

Animals↗

PubMed1996

Responses of auditory nerve fibers of the unanesthetized decerebrate cat to click pairs as simulated echoes.

1. To elucidate the peripheral contribution to "echo" processing in the auditory system, we examined the characteristics of auditory nerve responses to click-pair stimuli in unanesthetized, decerebrate cats. We used equilevel click pairs at peak levels of 45, 65, and 85 dB SPL re 20 microPa. The interclick intervals ranged from 1 to 32 ms. This study reports results from 78 auditory nerve fibers in 7 cats. The fibers were divided into 2 groups: 33 low- and 45 high-spontaneous rate (SR), with SRs less than and > or = 20 spikes/s, respectively. A method was introduced to quantify the second-click response, and its recovery was examined as a function of the interclick interval. 2. In general, auditory nerve fibers showed a gradual recovery of the second-click response as interclick interval was increased. Noticeable differences in the second-click response recovery functions emerged among fiber populations that were related to the SR. Low-SR fibers showed little change in the recovery functions of the second-click response as the click level was increased from 45 to 85 dB SPL. In contrast, high-SR fibers showed slower recoveries with increasing click level from 45 to 85 dB SPL. At 45 and 65 dB SPL, the recovery functions of the two SR groups were similar. At 85 dB SPL, high-SR fibers exhibited slower recovery than low-SR fibers, regardless of fiber characteristic frequency. The interclick intervals at 50% second-click response ranged from 1 to 6 ms (mean, 1.4 ms) among low-SR fibers. The interclick intervals at 50% second-click response for high-SR fibers, whereas similar to those for the low-SR fibers at 45 and 65 dB SPL, ranged from 2 to 16 ms (mean, 3 ms) for high-SR fibers, at 85 dB SPL. 3. We also examined auditory nerve compound action potentials (CAPs) evoked by click-pair stimuli for various interclick intervals and click levels. With increasing interclick interval, the amplitude of the second-click CAP increased, and with increasing level, the second-click CAP showed slower recovery. At 45 dB SPL, the recovery functions of the second-click CAP were similar to those of the high- and low-SR fibers. At higher levels, the CAP exhibited lower second-click response values than both high- and low-SR fiber populations for interclick intervals < 4-8 ms. At 85 dB SPL, as interclick interval increased, between 8 and 16 ms, the CAP second-click response converged with that of the high-SR fibers, and by 32 ms, the second-click response values were similar for the CAP, high- and low-SR fibers. 4. The present results are consistent with those of forward masking studies at the level of the auditory nerve in that both demonstrate a short-term reduction of the neural responses. However, the two results differ in that we observed that high-SR fibers exhibited slower recovery than low-SR fibers in response to click-pair stimuli, opposite of the trend observed in the forward masking studies of responses to pure-tone bursts. 5. The present results on auditory nerve fiber responses to click-pair stimuli provide a reference for comparison with responses of central auditory neurons to similar stimuli. This information should serve to elucidate the peripheral contribution to the processing of echoes in the auditory system.

Acoustic Stimulation↗

PubMed1996

Distortion product otoacoustic emission test of sensorineural hearing loss in humans: comparison of unequal- and equal-level stimuli.

Distortion product otoacoustic emissions (DPOEs) at the frequency of 2f1 -f2 (f1 < f2) were measured in 77 human adult ears with normal hearing or sensorineural hearing loss. The purpose of this study was to compare the performances of DPOE tests conducted with two sets of stimuli: 1) L1 = 65, L2 = 50 dB sound pressure level (SPL) re 20 microPa ("65/50"), and 2) L1 = L2 = 65 dB SPL ("65/65"). Half-octave DPOE root-mean-square levels at 1,000, 2,000, 4,000, and 6,000 Hz were computed from the initial DPOEs measured at 0.25-octave intervals. Correlation coefficient and decision-theory analyses were applied to evaluate the DPOE test performance. For both stimuli, DPOE level exhibited significant correlation with pure tone hearing threshold. When the criterion DPOE level distinguishing normal from impaired hearing was adjusted, the curves of sensitivity and specificity crossed, and the values at the crossing were higher than 80% at frequencies of 2,000 to 6,000 Hz for both stimuli. The area under the receiver operating characteristic (ROC) curve, which provides an overall evaluation of the test performance independent of the criterion DPOE level, was .90 or higher at 2,000 to 6,000 Hz for both stimuli. At 2,000 and 4,000 Hz, all measures of test performance were higher for the 65/50 stimulus than the 65/65 stimulus: area under the ROC curve (.96 to .97 versus .90 to .91, statistically significant, p < .001, Wilcoxon test), sensitivity/specificity (90% to 93% versus 80% to 85%), and correlation coefficient (.78 to .87 versus .66 to .79). At 1,000 and 6,000 Hz, the performances of the DPOE tests were similar for the two stimuli. These results support the conclusion that a DPOE test with L1 = 65 and L2 = 50 dB SPL provides a better performance than that with L1 = L2 = 65 dB SPL and recommend the use of stimuli with L1 being higher than L2 by about 15 dB. These results also support a growing view that 2f1-f2 DPOEs can be utilized clinically as a reliable method of testing human sensorineural hearing loss.

Acoustic Impedance Tests↗

PubMed1996

Distortion product otoacoustic emission test of sensorineural hearing loss: performance regarding sensitivity, specificity and receiver operating characteristics.

The performance of distortion product otoacoustic emissions (DPOEs) as a frequency-specific test of sensorineural hearing loss was evaluated in 142 ears of human adults with normal middle-ear function. The DPOE was measured with the stimulus levels of the two tones equal to 65 dB SPL (re 20 mu Pa) and the ratio between the two frequencies 1.2. In the DPOE test, the cochlear function of an ear at a test frequency was predicted to be normal or abnormal depending upon whether the DPOE level with the geometric mean of the two stimulus frequencies at the test frequency was greater or less than a criterion. The DPOE test outcomes were evaluated against the pure-tone hearing threshold as the standard. We found the sensitivity, specificity and predictive efficiency of the test to be 85-89% at 6000 and 4000 Hz, 82-83% at 2000 Hz and 78-79% at 1000 Hz, respectively. The performance was also evaluated using decision theory in terms of the area under the receiver operating characteristics. The latter was found to range from 0.90 (for 1000 Hz) to 0.94 (for 6000 Hz). These findings support the conclusion that the DPOEs can form a useful frequency-specific objective test of cochlear function.

Acoustic Impedance Tests↗

PubMed1996

Marginal shell of the anteroventral cochlear nucleus: acoustically weakly-driven and not-driven units in the unanesthetized decerebrate cat.

The ventral cochlear nucleus (VCN) of the cat is encapsulated by a marginal shell which is anatomically distinct from the central core of the VCN. Physiologically, little is known about the marginal shell. We report here a new finding that the marginal shell of the anteroventral cochlear nucleus (AVCN) in the unanesthetized decerebrate cat contains neural units which were weakly driven or not driven acoustically. The locations of the single units were histologically determined. Our observations also included other neural units of the marginal shell which were strongly driven acoustically; the latter results will be reported separately. The present physiological findings, together with previous anatomical findings of vestibular and somatosensory inputs to the AVCN marginal shell, suggest that some neurons of the AVCN marginal shell receive non-auditory sensory inputs besides weak auditory inputs and that these may play a role in multi-sensory processing.

Acoustic Stimulation↗