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PubMed2002

The auditory evoked magnetic fields to very high frequency tones.

We studied the auditory evoked magnetic fields (AEFs) in response to pure tones especially at very high frequencies (from 4000 Hz to 40,000 Hz). This is the first systematic study of AEFs using tones above 5000 Hz, the upper audible range of humans, and ultrasound. We performed two experiments. In the first, AEFs were recorded in 12 subjects from both hemispheres under binaural listening conditions. Six types of auditory stimulus (pure tones of five different frequencies: 4000 Hz, 8000 Hz, 10,000 Hz, 12,000 Hz, 14,000 Hz, and a click sound as the target stimulus) were used. In the second experiment, we used 1000 Hz, 15,000 Hz, and two ultrasounds with frequencies of 20,000 Hz and 40,000 Hz. The subjects could detect all stimuli in the first experiment but not the ultrasounds in the second experiment. We analyzed N1m, the main response with approximately 100 ms in peak latency, and made the following findings. (1) N1m responses to the tones up to 12,000 Hz were clearly recorded from at least one hemisphere in all 12 subjects. N1m for 14,000 Hz was identified in at least one hemisphere in 10 subjects, and in both hemispheres in six subjects. No significant response could be identified to ultrasounds over 20,000 Hz. (2) The amplitude of the N1m to the tones above 8000 Hz was significantly smaller than that to 4000 Hz in both hemispheres. There was a tendency for the peak latency of the N1m to be longer for the tones with higher frequencies, but no significant change was found. (3) The equivalent current dipole (ECD) of the N1m was located in the auditory cortex. There was a tendency for the ECD for the tones with higher frequencies to lie in more medial and posterior areas, but no significant change was found. (4) As for the interhemispheric difference, the N1m amplitude for all frequency tones was significantly larger and the ECDs were estimated to be located more anterior and medial in the right hemisphere than the left. The priority of the right hemisphere, that is the larger amplitude, for very high frequency tones was confirmed. (5) The orientation of the ECD in the left hemisphere became significantly more vertical the higher the tones. This result was consistent with previous studies which revealed the sensitivity of the frequency difference in the left hemisphere. From these findings we suggest that tonotopy in the auditory cortex exists up to the upper limit of audible range within the small area, where the directly air-conducted ultrasounds are not reflected.

Acoustic Stimulation↗
PubMed2002

Coding of auditory temporal and pitch information by hippocampal individual cells and cell assemblies in the rat.

This study reports how hippocampal individual cells and cell assemblies cooperate for neural coding of pitch and temporal information in memory processes for auditory stimuli. Each rat performed two tasks, one requiring discrimination of auditory pitch (high or low) and the other requiring discrimination of their duration (long or short). Some CA1 and CA3 complex-spike neurons showed task-related differential activity between the high and low tones in only the pitch-discrimination task. However, without exception, neurons which showed task-related differential activity between the long and short tones in the duration-discrimination task were always task-related neurons in the pitch-discrimination task. These results suggest that temporal information (long or short), in contrast to pitch information (high or low), cannot be coded independently by specific neurons. The results also indicate that the two different behavioral tasks cannot be fully differentiated by the task-related single neurons alone and suggest a model of cell-assembly coding of the tasks. Cross-correlation analysis among activities of simultaneously recorded multiple neurons supported the suggested cell-assembly model.Considering those results, this study concludes that dual coding by hippocampal single neurons and cell assemblies is working in memory processing of pitch and temporal information of auditory stimuli. The single neurons encode both auditory pitches and their temporal lengths and the cell assemblies encode types of tasks (contexts or situations) in which the pitch and the temporal information are processed.

Acoustic Stimulation↗
PubMed2002

Hemispheric specialization of linguistic pitch patterns.

Pitch is used to signal different aspects of language such as speaker identity, intonation, emphatic stress, and word identity (as signaled by lexical tones). This article reviews research studies investigating hemispheric specialization of these pitch patterns in the context of two competing hypotheses. The functional hypothesis states that pitch patterns are lateralized to different hemispheres of the brain depending on their functions. Those pitch patterns that carry a greater linguistic load (e.g., lexical tones) are lateralized to the left hemisphere, while those that carry a less linguistic load (e.g., intonation patterns signaling affective moods) are lateralized to the right hemisphere. The alternative hypothesis, the acoustic hypothesis, states that all pitch patterns, regardless of their functions, are lateralized to one hemisphere (the right hemisphere in particular). Although most researchers support the functional hypothesis, a comprehensive review, which includes lesion, dichotic-listening, and functional imaging studies of different types of pitch patterns, does not support this view. Moreover, little evidence exists for the alternative hypothesis. Possible methodological problems of these studies, alternative hypotheses, and considerations for future research are noted.

Functional Laterality↗
PubMed1984

[Characteristics of middle-latency auditory evoked potentials in awake and anesthetized patients].

Late auditory evoked potentials (50-500 msec latency) can be evoked by tonal stimuli but their instability prevents their use in many clinical situations. In contrast, the early responses (up to 10 msec) are stable, regardless of sleep or sedation, but they can only be evoked by transient, non-tonal stimuli. Therefore neither type may be used for an evaluation of frequency thresholds. The middle latency responses represent a compromise: first, they can be evoked by tonal stimuli of the tone-pip type and, second, they are relatively stable. For these reasons the authors have carried out a general study on the middle latency responses in subjects with normal hearing, in patients with impaired hearing and in patients under a variety of surgical anesthesia. The middle latency response evoked by clicks and tone-pips (4 sines of 500, 1000, 2000 and 4000 Hz) have a series of characteristic waves named, according to their latency, A(V), B(No), C(Po), D(Na), E(Pa). The threshold of visual detection for these potentials is situated near that of the psycho-acoustic threshold (0-20 dB). The authors point out the clinical utilization of the middle latency response especially in cases in which one desires an objective evaluation of the auditory threshold in the lower frequency range. It is important to know that the middle latency response remains present using some types of anesthesia (Ketalar, ataralgesy), disappears partially with neuroleptanesthesia and completely with inhalation anesthesia (fluothane, halothane).

Adult↗
PubMed2001

Psychophysics of a prototype peri-modiolar cochlear implant electrode array.

Psychophysical measurements were performed in three hearing-impaired adult subjects implanted with a CI22 cochlear prosthesis (Cochlear Ltd.) fitted with a developmental peri-modiolar electrode array. The array was manufactured with a curvature approximating that of the inner wall of the scala tympani but, after straightening and insertion, lay on average about half way between the inner and outer walls of the scala. All subjects were tested with bipolar stimulation; two were also tested with monopolar, employing the most basal electrode as the return. Maximum comfortable level and threshold reduced with decreasing distance of electrode from the modiolus, whereas dynamic range increased. The linearity of the loudness growth function did not vary significantly with electrode position but the function was more non-linear for lower maximum comfortable levels. Current level discrimination, normalized with respect to dynamic range, improved with decreasing distance of electrode from the modiolus in two subjects. Pitch varied regularly with insertion depth of the stimulated electrode for bipolar stimulation in two subjects and also for monopolar stimulation in one subject. Electrode discrimination was enhanced by closeness to the modiolus. Whereas the forward masking patterns for bipolar stimulation of electrodes close to the modiolus had a sharp double-peaked structure, those for monopolar stimulation were flatter and had a single peak.

Adult↗
PubMed2002

Temporal pitch in electric hearing.

Both place and temporal codes in the peripheral auditory system contain pitch information, however, their actual use by the brain is unclear. Here pitch data are reported from users of the cochlear implant, which provides the ability to change the temporal code independently from the place code. With fixed electrode stimulation, both frequency discrimination and pitch estimate data show that the cochlear implant users can only discern differences in pitch for frequencies up to about 300 Hz. An integration model can predict pitch estimation from frequency discrimination, reinforcing Fechner's hypothesis relating sensation magnitude to stimulus discriminability. The present results suggest that 300 Hz is the upper boundary of the temporal code and that the absolute place information should be included in the present pitch models. They further suggest that future cochlear implants need to increase the number of independent electrodes to restore normal pitch range and resolution.

Adult↗
PubMed2003

How does tripus extirpation affect auditory sensitivity in goldfish?

Otophysine fishes are characterized by Weberian ossicles connecting the swimbladder to the ear acoustically. In order to determine the degree to which these ossicles contribute to auditory sensitivity, the tripus was unilaterally or bilaterally extirpated in goldfish and hearing thresholds determined. The auditory evoked potential (AEP) recording technique was used to measure auditory sensitivity between 100 and 4000 Hz. Bilateral extirpation resulted in a hearing loss at all frequencies ranging from 7 dB at 100 Hz to 33 dB at 2 kHz; no AEPs were detectable at 4 kHz. In contrast to bilateral extirpation, unilateral tripus removal caused no sensitivity change. Pre-exposure to intense white noise caused different threshold shifts in unilaterally versus bilaterally extirpated goldfish. Thresholds increased at all frequencies in unilaterally extirpated goldfish but only at 100 and 200 Hz after bilateral extirpation. The comparison between the hearing generalist Neolamprologus brichardi (family Cichlidae) and the tripus-extirpated otophysine revealed that the latter is still more sensitive than the cichlid. Higher sensitivity in the goldfish after bilateral extirpation as compared to swimbladder elimination indicates that swimbladder oscillations might partly be transmitted to the inner ear independently of the ossicular chain. This suggests that the auditory system in otophysines improves with increasing frequency due to a more efficient connection between the swimbladder and inner ear ensured by the Weberian ossicles.

Air Sacs↗
PubMed2003

Hearing in American leaf-nosed bats. III: Artibeus jamaicensis.

We determined the audiogram of the Jamaican fruit-eating bat (Phyllostomidae: Artibeus jamaicensis), a relatively large (40-50 g) species that, like other phyllostomids, uses low-intensity echolocation calls. A conditioned suppression/avoidance procedure with a fruit juice reward was used for testing. At 60 dB SPL the hearing range of A. jamaicensis extends from 2.8 to 131 kHz, with an average best sensitivity of 8.5 dB SPL at 16 kHz. Although their echolocation calls are low-intensity, the absolute sensitivity of A. jamaicensis and other 'whispering' bats does not differ from that of other mammals, including other bats. The high-frequency hearing of A. jamaicensis and other Microchiroptera is slightly higher than expected on the basis of selective pressure for passive sound localization. Analysis suggests that the evolution of echolocation may have been accompanied by the extension of their high-frequency hearing by an average of one-half octave. With respect to low-frequency hearing, all bats tested so far belong to the group of mammals with poor low-frequency hearing, i.e., those unable to hear below 500 Hz.

Animals↗
PubMed2004

Isoflurane/N2O anesthesia suppresses narrowband but not wideband inhibition in dorsal cochlear nucleus.

Anesthesia alters the response properties of neurons in the dorsal cochlear nucleus (DCN). Barbiturates decrease spontaneous activity and the prevalence of inhibitory responses, so that DCN principal cells show less inhibition by narrowband stimuli (e.g. tones at best frequency). Here we present the effects on cat DCN of anesthesia using isoflurane plus nitrous oxide (N2O). Because the cellular anesthetic mechanisms of isoflurane differ from those of pentobarbital, the effects of the two anesthetics in DCN might be different. The strength of two inhibitory circuits in the DCN, the narrowband and wideband inhibitor, were studied and compared with results in unanesthetized decerebrate animals. The primary effects of isoflurane/N2O anesthesia were to lower spontaneous activity and increase the thresholds of units. All the response types seen in the decerebrate preparation were also seen with isoflurane/N2O, but the prevalence of predominantly inhibitory responses to narrowband stimuli (type IV units) decreased (from approximately 31% to approximately 11%). However, responses to band-reject noise were similar to those seen in unanesthetized animals. Together, these results suggest that the effects of isoflurane/N2O are primarily on the narrowband inhibitory circuit, rather than the wideband inhibitor.

Anesthetics, Inhalation↗
PubMed1996

Pitch comparisons of acoustically and electrically evoked auditory sensations.

Cochlear implant users with some residual hearing in the non-implanted ear compared the pitch sensations produced by acoustic pure tones and pulsatile electric stimuli. Pitch comparisons were obtained for pure tones and electrical stimuli presented at different positions (electrodes) in the scala tympani, keeping the electric pulse rate fixed at 100, 250, or 800 pps. Similarly, pitch comparisons were obtained for electrical stimuli with variable pulse rates presented to two fixed electrode positions (apical and basal) in the cochlea. Both electrode position and pulse rate influenced the perceived pitch of the electrical signal and 'matched' electric and acoustic signals were found over a wide range of frequencies. There was a large variation between listeners. For some stimuli, listeners had difficulty in deciding whether the acoustic or electric stimulus was higher in pitch. Despite the variability, consistent trends were obtained from the data: higher frequencies tended to be matched by more basal electrodes for all pulse rates. Higher frequencies tended to be matched by higher pulse rates for both electrode positions. The electrode positions that 'matched' pure tones were more basal than predicted from the characteristic frequency coordinates of the basilar membrane in a normal human cochlea.

Acoustic Stimulation↗
PubMed1996

Auditory nerve neurophonic produced by the frequency difference of two simultaneously presented tones.

When two phase-locked sinusoidal stimuli having frequencies of F1 and F2 are simultaneously introduced to the ear of the gerbil, a difference tone (DT) can be observed (DT = F2-F1, where F2 > F1) in the time-averaged electrical response recorded from the cochlear round window (RW). Tetrodotoxin (TTX), which blocks the axonal firing of the cochlear nerve fiber, greatly attenuates this DT response, suggesting it is primarily neural in origin. Alternating the polarity of a single phase-locked tone cancels out the RW cochlear microphonic (CM) from the time-averaged response, leaving a residual auditory nerve neurophonic (ANN) response if the stimulus frequency is low enough to result in phase-locked firing of cochlear nerve axons. Simultaneous presentation of 1 kHz (F1) and 2 kHz (F2) tones, each being phase-locked with alternating polarity, produces a small ANN in response to the original tones and a large time-averaged ANN in response to the DT. Even when the frequency of the individual tones is too high to support phase-locking, a large DT-ANN can also be measured in response to simultaneously presented tones. A robust time-averaged DT-ANN can be measured when the temporal and intensity relationships between F1 and F2 are varied widely, with the latency (but not amplitude) of the response following the stimulus envelope. The DT-ANN produced by pairs of tones having frequencies ranging from 500 Hz to 3.5 kHz is largest in response to a DT of approximately 700-1100 Hz. This is in contrast to the ANN generated in response to a single tone, which decreases in magnitude as the stimulus frequency increases from 500 to 1500 Hz. Robust DT-ANNs can be measured from the gerbil even when the F2 frequency is greater than 30 kHz.

Acoustic Stimulation↗
PubMed1999

Reversed tonotopic map of the basilar papilla in Gekko gecko.

A published model of the frequency responses of different locations on the basilar papilla of the Tokay gecko Gekko gecko (Authier and Manley, 1995. Hear. Res. 82, 1-13) had implied that (a) unlike all other amniotes studied so far, the frequency map is reversed, with the low frequencies at the base and the high frequencies at the apex, and (b) the high-frequency area is split into two parallel-lying hair cell areas covering different frequency ranges. To test these hypotheses, the frequency representation along the basilar papilla of Gekko gecko was studied by recording from single auditory afferent nerve fibers and labelling them iontophoretically with horseradish peroxidase. Successfully labelled fibers covered a range of characteristic frequencies from 0.42 to 4.9 kHz, which extended from 78% to 9% of the total papillar length, as measured from the apex. The termination sites of labelled fibers within the basilar papilla correlated with their characteristic frequency, the lowest frequencies being represented basally, and the highest apically. This confirms the first prediction of the model. The map indicates, however, that one of the two high-frequency papillar regions (the postaxial segment) represents the full high-frequency range, from about 1 to 5 kHz. No functionally identified labelling was achieved in the preaxial segment. Thus the assumptions underlying the proposed model need revision. A good mathematical description of the frequency distribution was given by an exponential regression with a mapping constant in the living state of approximately 0.4 mm/octave.

Animals↗
PubMed1999

Do auditory responses recorded from awake animals reflect the anatomical parcellation of the auditory thalamus?

Previous studies performed in anesthetized animals have shown differences between the acoustic responses of neurons recorded from the different divisions of the medial geniculate body (MGB). This study aimed at determining whether or not such differences are also expressed when neurons are recorded from awake animals. The auditory responses of 130 neurons of the auditory thalamus were determined in awake, restrained guinea pigs while the state of vigilance of the animals was continuously monitored. There were significantly more 'on' phasic evoked responses and significantly fewer 'non-responsive' or 'labile' cells in the ventral division of the MGB (MGv) than in the other divisions. The response latencies and the variability of the latencies were smaller in the MGv than in the other divisions. The tuning of the neurons obtained from MGv and from the lateral part of the posterior complex were significantly sharper than those coming from the dorsal division of the MGB and the medial division. The mean threshold and the percentage of monotonic vs. non-monotonic intensity functions were not different in the subdivisions of the auditory thalamus. When compared with previous studies, the quantifications of the acoustic responses obtained in the present study gave values that differed from those reported under deep anesthesia, but were close to those reported under light anesthesia. Lastly, even if none of the physiological characteristic makes it possible, by itself, to determine the locus of recordings in the auditory thalamus, we conclude that the physiological characteristics of the evoked responses obtained in MGv differ from those of other divisions.

Acoustic Stimulation↗
PubMed1999

Responses of auditory nerve fibers innervating regenerated hair cells after local application of gentamicin at the round window of the cochlea in the pigeon.

Hair cells in the basilar papilla of birds have the capacity to regenerate after injury. There is also functional recovery of hearing after regeneration of the hair cells. The present study was undertaken to determine the effect of local aminoglycoside application on the physiology of auditory nerve fibers innervating regenerated hair cells. Collagen sponges loaded with gentamicin were placed at the round window of the cochlea in adult pigeons. The local application of gentamicin-loaded collagen sponges resulted in total hair cell loss over at least the basal 62% of the basilar papilla. According to the pigeon cochlear place-frequency map (Smolders, Ding-Pfennigdorff and Klinke, Hear. Res. 92 (1995) 151-169), frequencies above 0.3 kHz are represented in this area. Physiological data on single auditory nerve fibers were obtained 14 weeks after gentamicin treatment. The response properties showed the following characteristics when compared to control data: CF thresholds (CF = characteristic frequency) were elevated in units with CF above 0.15 kHz, sharpness of tuning (Q10dB) was reduced in units with CF above 0.38 kHz, low-frequency slopes of the tuning curves were reduced in units with CF above 0.25 kHz, high frequency slopes of the tuning curves were reduced in units with CF above 0.4 kHz, spontaneous firing rate was reduced in units with CF above 0.38 kHz, dynamic range of rate-intensity functions at CF was reduced in units with CF above 0.4 kHz and the slopes of these rate-intensity functions were elevated in units with CF above 0.4 kHz. Maximum discharge rate was the only parameter that remained unchanged in regenerated ears. The results show that the response properties of auditory nerve fibers which innervate areas of the papilla that were previously devoid of hair cells are poorer than the controls, but that action potential generation in the afferent fibers is unaffected. This suggests that despite structural regeneration of the basilar papilla, functional recovery of the auditory periphery is incomplete at the level of the hair cell or the hair cell-afferent synapse.

Administration, Topical↗
PubMed2003

Central tinnitus.

Tinnitus is likely initiated by a discontinuity in the spontaneous or low-level-stimulus induced neural activity across auditory nerve fibers with different characteristic frequency (CF). This discontinuity may be caused by functional loss of outer hair cells in those regions where inner hair cells are preserved. The reduced spontaneous activity for nerve fibers with CFs in the hearing loss range may result in a reduction of lateral inhibition at more central levels. This reduced lateral inhibition of neurons with CFs close to the edge frequency of the audiogram induces hypersensitivity and hyperactivity in these neurons. Persistent changes in lateral inhibition result in increased numbers of neurons that are tuned to a limited range of frequencies at the edge of the cochlear lesion. Thus, the frequency map in auditory cortex, the tonotopic map, becomes reorganized as it reflects these changes. The spontaneous neuronal firings in the auditory cortex after insults that cause tinnitus show increased synchrony, thereby mimicking one aspect of the responses to normal sound stimulation. All long-standing tinnitus may thus be called central tinnitus, despite the fact that it is initiated by cochlear hearing loss or is localized to the hearing loss ear.

Auditory Cortex↗
PubMed1997

The effect of intravenous lidocaine injection on hearing thresholds.

The effect of intravenous injection of lidocaine on hearing thresholds was studied in normal subjects. Continuous and intermittent tones at 1, 4 and 8 kHz were used as stimuli and the threshold change with lidocaine injection was measured using a self-recording audiometer (Békésy audiometer). Both increases and decreases in the threshold were observed. The former occurred more frequently than the latter. In cases of a threshold increase, lidocaine injection exhibited a frequency specific effect; the higher the frequency, the more often the threshold was increased by lidocaine injection. There was no significant difference in threshold changes between continuous and intermittent tones. The present results suggest that lidocaine may act on the inner ear hair cells.

Adult↗
PubMed1997

Choice of a tone-pip envelope for frequency-specific threshold evaluations by means of the middle-latency response: normally hearing subjects and slope of sensorineural hearing loss.

The effects of stimulus rise-fall and plateau times on the middle-latency response (MLR) waveform (Na-Pa amplitude and Pa latency) were investigated in 14 normally hearing subjects and an objective MLR threshold was evaluated at low and middle frequencies in ten normally hearing subjects and ten patients with slope of sensorineural hearing loss, using a selected stimulus-envelope time. After analyzing the effects of envelope times on the MLR waveform and the spectra of tone-pips, it was found that a rise-fall time of 4 ms with a plateau of 2 ms (4-2-4) is an acceptable compromise between a synchronous discharge and frequency specificity for estimating the MLR threshold. The MLR threshold produced by 4-2-4 tone-pips approximated the psychoacoustic threshold at low and middle frequencies in the normal and hearing impaired subjects. This demonstrates the clinical usefulness of the MLR in estimating low- and middle-frequency thresholds.

Adult↗
PubMed2001

Discrimination functions: can they be used to classify singing voices?

Researchers long have searched for invariant acoustic features that can be used to identify singing voice categories or even individual singers. Few researchers have examined how listeners perceive singing voice categories or individual voices. Timbre, the most studied perceptual dimension of the singing voice, is generally believed to vary systematically between singing voice categories but is often assumed to be invariant with an individual singer. To test this assumption, 2 mezzo-sopranos and 2 sopranos were recorded singing the vowel /a/ on the pitches A3, C4, G4, B4, F5, and A5. Trials of three stimuli were constructed. Two of the three stimuli in each trial were produced by the same singer at two different pitches (X1 and X2), while the third stimulus was produced by a different singer (Y). Three X1X2 conditions were created: (1) G4, B4; (2) C4, F5; and (3) A3, A5. For each singer and each condition, Y was varied across the three remaining singers and across all six pitches. Experienced and inexperienced listeners were asked to identify which stimulus was produced by the "odd" person. The ability to correctly choose the odd person varied greatly depending on pitch factors, suggesting that the traditional concept of an invariant timbre associated with a singer is inaccurate and that vocal timbre must be conceptualized in terms of transformations in perceived quality that occur across an individual singer's range and/or registers.

Adult↗