Otoferlin is involved in neurotransmitter release at the synapse between inner hair cells (IHCs) and auditory nerve fibres, and mutations in the
OTOF
gene result in severe to profound hearing loss. ...Abnormal sound-evoked cochlear potentials were recorded with transtympanic electrocochleography from four children with otoferlin (
OTOF
) mutations to evaluate physiological effects in humans of abnormal neurotransmitter release from IHCs. The subjects were profoundly deaf with absent auditory brainstem responses and preserved otoacoustic emissions consistent with auditory neuropathy. Two children were compound heterozygotes for mutations c.2732_2735dupAGCT and p.Ala964Glu; one subject was homozygous for mutation p.Phe1795Cys, and one was compound heterozygote for two novel mutations c.1609delG in exon 16 and c.1966delC in exon 18. Cochlear potentials evoked by clicks from 60 to 120 dB peak equivalent sound pressure level were compared to recordings obtained from 16 normally hearing children. Cochlear microphonic (CM) was recorded with normal amplitudes from all but one ear. After cancelling CM, cochlear potentials were of negative polarity with reduced amplitude and prolonged duration compared to controls. These cochlear potentials were recorded as low as 50–90 dB below behavioural thresholds in contrast to the close correlation in controls between cochlear potentials and behavioural threshold. Summating potential was identified in five out of eight ears with normal latency whilst auditory nerve compound action potentials were either absent or of low amplitude. Stimulation at high rates reduced amplitude and duration of the prolonged potentials, consistent with neural generation. This study suggests that mechano-electrical transduction and cochlear amplification are normal in patients with
OTOF
mutations. The low-amplitude prolonged negative potentials are consistent with decreased neurotransmitter release resulting in abnormal dendritic activation and impairment of auditory nerve firing.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract Objectives To examine auditory cortical potentials in normal-hearing subjects to intensity increments in a continuous pure tone at low, mid, and high frequency. Methods Electrical scalp ...potentials were recorded in response to randomly occurring 100 ms intensity increments of continuous 250, 1000, and 4000 Hz tones every 1.4 s. The magnitude of intensity change varied between 0, 2, 4, 6, and 8 dB above the 80 dB SPL continuous tone. Results Potentials included N100, P200, and a slow negative (SN) wave. N100 latencies were delayed whereas amplitudes were not affected for 250 Hz compared to 1000 and 4000 Hz. Functions relating the magnitude of the intensity change and N100 latency/amplitude did not differ in their slope among the three frequencies. No consistent relationship between intensity increment and SN was observed. Cortical dipole sources for N100 did not differ in location or orientation between the three frequencies. Conclusions The relationship between intensity increments and N100 latency/amplitude did not differ between tonal frequencies. A cortical tonotopic arrangement was not observed for intensity increments. Our results are in contrast to prior studies of brain activities to brief frequency changes showing cortical tonotopic organization. Significance These results suggest that intensity and frequency discrimination employ distinct central processes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Binaural interaction in the brainstem and middle latency auditory evoked potentials to intensity (d
I) and timing differences (d
T) between the two ears was studied in 10 normal hearing young adults. ...A component reflecting binaural interaction in the brainstem potentials occurred at approximately 7 ms and was of largest amplitude when d
I and d
T were 0. The latency of the binaural interaction component gradually shifted and its amplitude decreased as d
I or d
T increased and binaural interaction became undetectable when d
I = 16 dB or when d
T ≥ 1.6 ms. In the middle latency potentials binaural interaction components peaking at 20, 32, and 45 ms were defined that were also largest when d
I and d
T = 0. The latency of the interaction did not shift with changes in d
T and d
I whereas the amplitude gradually decreased but binaural interaction components were still evident even at the largest values of d
I (30 dB) and d
T (3 ms). Psychophysical judgements of binaural perceptions showed binaural fusion of the stimuli to persist with d
T values up to 1.6 ms and that lateralization of the intracranial image was complete when either d
T = 1.6 ms or when d
I = 16 dB. The results suggest that the presence of a binaural interaction component of auditory brainstem potentials correlates with the fusion of binaural click stimuli and the amplitude of the binaural interaction component correlates inversely with the degree of lateralization of the intracranial image. Binaural interaction components of middle latency potentials persist and continue to change even after the binaural stimuli cannot be fused.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
OBJECTIVEThe objective of this e-periment was to address1) whether normal efferent system function is required for normal cochlear tuning as measured by distortion product otoacoustic emission ...(DPOAE) suppression in humans and 2) whether cochlear function, assessed by DPOAE suppression tuning, is normal in a small group of patients with auditory neuropathy.
DESIGNDPOAE suppression tuning curves (STCs) are similar to other physiologic measures of tuning. They are generated by evoking a DPOAE with two simultaneously presented pure tones and then suppressing the distortion product with a third tone of varying frequency and level. In this study, DPOAE STCs were generated with f2 frequencies of 1500, 3000, and 6000 Hz in 15 normal-hearing adults and four subjects with documented auditory neuropathy. Tuning curve width, slope and tip characteristics, as well as rate of suppression growth were measured in each group. Contralateral suppression of otoacoustic emissions (OAEs) was also recorded as an inde- of medial efferent function.
RESULTSResults show that the four subjects with auditory neuropathy lacked efferent suppression of OAEs. However, these four subjects showed normal estimates of cochlear tuning as measured by DPOAE suppression results.
CONCLUSIONSThis finding suggests that normal efferent system function is not required at the time of test for normal DPOAE suppression tuning. It also suggests that cochlear function as evaluated by detailed measures of DPOAE suppression, is normal in these “typical” patients with auditory neuropathy.
To study objectively auditory temporal processing in a group of normal hearing subjects and in a group of hearing-impaired individuals with auditory neuropathy (AN) using electrophysiological and ...psychoacoustic methods.
Scalp recorded evoked potentials were measured to brief silent intervals (gaps) varying between 2 and 50
ms embedded in continuous noise. Latencies and amplitudes of N100 and P200 were measured and analyzed in two conditions: (1) active, when using a button in response to gaps; (2) passive, listening, but not responding.
In normal subjects evoked potentials (N100/P200 components) were recorded in response to gaps as short as 5
ms in both active and passive conditions. Gap evoked potentials in AN subjects appeared only with prolonged gap durations (10–50
ms). There was a close association between gap detection thresholds measured psychoacoustically and electrophysiologically in both normals and in AN subjects.
Auditory cortical potentials can provide objective measures of auditory temporal processes.
The combination of electrophysiological and psychoacoustic methods converged to provide useful objective measures for studying auditory cortical temporal processing in normals and hearing-impaired individuals. The procedure used may also provide objective measures of temporal processing for evaluating special populations such as children who may not be able to provide subjective responses.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This study investigates the effects of musical training on brain activity to violations of rhythmic expectancies. We recorded behavioral and event-related brain potential (ERP) responses of musicians ...and non-musicians to discrepancies of rhythm between pairs of unfamiliar melodies based on Western classical rules. Rhythm deviations in the second melody involved prolongation of a note, thus creating a delay in the subsequent note; the duration of the second note was consequently shorter because the offset time was unchanged. In the first melody, on the other hand, the two notes were of equal duration. Musicians detected rhythm deviations significantly better than non-musicians. A negative auditory cortical potential in response to the omitted stimulus was observed at a latency of 150-250 ms from where the note should have been. There were no significant differences of amplitude or latency between musicians and non-musicians. In contrast, the N100 and P200 to the delayed note after the omission were significantly greater in amplitude in musicians compared to non-musicians especially in frontal and frontal-central areas. These findings indicate that long term musical training enhances brain cortical activities involved in processing temporal irregularities of unfamiliar melodies.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This study investigates the effects of musical training on brain activity to violations of rhythmic expectancies. We recorded behavioral and event-related brain potential responses of musicians and ...nonmusicians to discrepancies of rhythm between pairs of unfamiliar melodies based on Western classical rules. Rhythm deviations in the second melody involved prolongation of a note, thus creating a delay in the subsequent note; the duration of the second note was consequently shorter because the offset time was unchanged. In the first melody, on the other hand, the 2 notes were of equal duration. Musicians detected rhythm deviations significantly better than nonmusicians. A negative auditory cortical potential in response to the omitted stimulus was observed at a latency of 150-250 ms from where the note should have been. There were no significant differences of amplitude or latency between musicians and nonmusicians. In contrast, the N100 and P200 to the delayed note after the omission were significantly greater in amplitude in musicians compared with nonmusicians especially in frontal and frontal-central areas. These findings indicate that long-term musical training enhances brain cortical activities involved in processing temporal irregularities of unfamiliar melodies.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
To study the effects of duration and intensity of noise that precedes gaps in noise on the N-Complex (N
1a and N
1b) of Event-Related Potentials (ERPs) to the gaps.
ERPs were recorded from 13 normal ...subjects in response to 20
ms gaps in 2–4.5
s segments of binaural white noise. Within each segment, the gaps appeared after 500, 1500, 2500 or 4000
ms of noise. Noise intensity was either 75, 60 or 45
dBnHL. Analysis included waveform peak measurements and intracranial source current density estimations, as well as statistical assessment of the effects of pre-gap noise duration and intensity on N
1a and N
1b and their estimated intracranial source activity.
The N-Complex was detected at about 100
ms under all stimulus conditions. Latencies of N
1a (at ∼90
ms) and N
1b (at ∼150
ms) were significantly affected by duration of the preceding noise. Both their amplitudes and the latency of N
1b were affected by the preceding noise intensity. Source current density was most prominent, under all stimulus conditions, in the vicinity of the temporo-parietal junction, with the first peak (N
1a) lateralized to the left hemisphere and the second peak (N
1b) – to the right. Additional sources with lower current density were more anterior, with a single peak spanning the duration of the N-Complex.
The N
1a and N
1b of the N-Complex of the ERPs to gaps in noise are affected by both duration and intensity of the pre-gap noise. The minimum noise duration required for the appearance of a double-peaked N-Complex is just under 500
ms, depending on noise intensity. N
1a and N
1b of the N-Complex are generated predominantly in opposite temporo-parietal brain areas: N
1a on the left and N
1b on the right.
Duration and intensity interact to define the dual peaked N-Complex, signaling the cessation of an ongoing sound.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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