N100m Latency Research Articles

N100m latency shortening caused by selective attention

The N100m response to a specific same-sound stimulus may be altered by the degree of attention paid to the stimulus. When participants selectively pay attention to the stimulus, the N100m amplitude increases; however, minimal effects are observed on the N100m latency. In this study, we examined the effects of selective special attention (motivation) to extract the frequency (or pitch) information from a probe tone on the N100m response to the probe tone. We compared the N100m latencies and amplitudes using magnetoencephalography, with the following three experimental conditions: 1) vocalization task protocol (vocalize in tune with the pitch of the probe tone after the presentation of the probe tone), 2) hearing task protocol (just listen to the probe tone), and 3) imagining (just imagine the vocalization in tune with the probe tone). The results indicated that the N100m latency in response to the probe tone was significantly shortened in the vocalization and imagining tasks compared with the hearing task in the right hemisphere of the brain. The amplitude was significantly increased in the vocalization task compared with the imagining and hearing tasks in the right hemisphere, and in the vocalization task compared with the hearing task in the left hemisphere of the brain; that is, the attention and/or motivation required to extract the information from the stimulus tones may have caused N100m latency shortening. To our knowledge, this study is the first to demonstrate that the N100m latency may be shortened under particular attentional conditions in response to a simple tone.

Abnormal auditory synchronization in stuttering: A magnetoencephalographic study

In a previous magnetoencephalographic study, we showed both functional and structural reorganization of the right auditory cortex and impaired left auditory cortex function in people who stutter (PWS). In the present work, we reevaluated the same dataset to further investigate how the right and left auditory cortices interact to compensate for stuttering. We evaluated bilateral N100m latencies as well as indices of local and inter-hemispheric phase synchronization of the auditory cortices. The left N100m latency was significantly prolonged relative to the right N100m latency in PWS, while healthy control participants did not show any inter-hemispheric differences in latency. A phase-locking factor (PLF) analysis, which indicates the degree of local phase synchronization, demonstrated enhanced alpha-band synchrony in the right auditory area of PWS. A phase-locking value (PLV) analysis of inter-hemispheric synchronization demonstrated significant elevations in the beta band between the right and left auditory cortices in PWS. In addition, right PLF and PLVs were positively correlated with stuttering frequency in PWS. Taken together, our data suggest that increased right hemispheric local phase synchronization and increased inter-hemispheric phase synchronization are electrophysiological correlates of a compensatory mechanism for impaired left auditory processing in PWS.

Positive auditory cortical responses in patients with absent brainstem response

ObjectiveTo compare the detectability of the different auditory evoked responses in patients with retrocochlear lesion. MethodsThe 40-Hz auditory steady state response (ASSR) and the N1m auditory cortical response were examined by magnetoencephalography in 4 patients with vestibular schwannoma, in whom the auditory brainstem response (ABR) was absent. ResultsApparent N1m responses were observed despite total absence of the ABR or absence except for small wave I in all patients, although the latency of N1m was delayed in most patients. On the other hand, clear ASSFs could be observed only in one patient. Very small 40-Hz ASSFs could be detected in 2 patients (amplitude less than 1fT), but no apparent ASSFs were observed in one patient, in whom maximum speech intelligibility was extremely low and the latency of N1m was most prolonged. ConclusionThe N1m response and 40-Hz ASSR could be detected in patients with absent ABR, but the N1m response appeared to be more detectable than the 40-Hz ASSR. SignificanceCombined assessment with several different evoked responses may be useful to evaluate the disease conditions of patients with retrocochlear lesions.

Neuromagnetic index of hemispheric asymmetry predicting long-term outcome in sudden hearing loss

The neuromagnetic index of hemispheric asymmetry in terms of ipsilateral/contralateral ratio at acute stage was previously revealed to prognosticate the 1-month hearing outcome of acute unilateral idiopathic sudden sensorineural hearing loss (ISSNHL), showing a dynamic relationship between top- and down-levels of auditory pathway. However, the prognostic effect of reorganization pattern for the long-term results remained elusive. This study aimed to probe the prognosticating relevance of hemispheric asymmetry to the hearing at chronic stage of ISSNHL. Using magnetoencephalography (MEG), inter-hemispheric differences in peak dipole of N100m responses to monaural tones were evaluated in 21 controls and 21 ISSNHL patients at initial and final (12 months later) stages. Predictive value of hemispheric asymmetry was assessed by correlating hearing level and ipsilateral/contralateral ratio (I/C) of N100m latency and amplitude. Healthy-side dominance of N100m was observed in ISSNHL initially, and remained in three final prognostic subgroups (complete, partial, and no recovery) of ISSNHL. The initial I/C(amplitude) on affected-ear stimulation strongly correlated with the hearing level of final stage in ISSNHL. However, there was no prognostic effect of hemispheric asymmetry pattern for the 12-month hearing improvement. The heterogeneity between neuromagnetic index and hearing levels possibly echoed different pathogeneses of ISSNHL. Since a restored hearing status did not necessarily lead toward a normal functional organization, the dynamics of hemispheric asymmetry could actually index a central resilient reorganization in the brain for sound processing in ISSNHL. Our finding showed not only a clinically relevant measure to predict final hearing of ISSNHL, but also a linkage between central plasticity and cochlear lesion. This finding suggests a new perspective, and perhaps new interventions, to diagnose and treat unilateral ISSNHL.

Neuromagnetic Index of Hemispheric Asymmetry Prognosticating the Outcome of Sudden Hearing Loss

The longitudinal relationship between central plastic changes and clinical presentations of peripheral hearing impairment remains unknown. Previously, we reported a unique plastic pattern of “healthy-side dominance” in acute unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). This study aimed to explore whether such hemispheric asymmetry bears any prognostic relevance to ISSNHL along the disease course. Using magnetoencephalography (MEG), inter-hemispheric differences in peak dipole amplitude and latency of N100m to monaural tones were evaluated in 21 controls and 21 ISSNHL patients at two stages: initial and fixed stage (1 month later). Dynamics/Prognostication of hemispheric asymmetry were assessed by the interplay between hearing level/hearing gain and ipsilateral/contralateral ratio (I/C) of N100m latency and amplitude. Healthy-side dominance of N100m amplitude was observed in ISSNHL initially. The pattern changed with disease process. There is a strong correlation between the hearing level at the fixed stage and initial I/Camplitude on affected-ear stimulation in ISSNHL. The optimal cut-off value with the best prognostication effect for the hearing improvement at the fixed stage was an initial I/Clatency on affected-ear stimulation of 1.34 (between subgroups of complete and partial recovery) and an initial I/Clatency on healthy-ear stimulation of 0.76 (between subgroups of partial and no recovery), respectively. This study suggested that a dynamic process of central auditory plasticity can be induced by peripheral lesions. The hemispheric asymmetry at the initial stage bears an excellent prognostic potential for the treatment outcomes and hearing level at the fixed stage in ISSNHL. Our study demonstrated that such brain signature of central auditory plasticity in terms of both N100m latency and amplitude at defined time can serve as a prognostication predictor for ISSNHL. Further studies are needed to explore the long-term temporal scenario of auditory hemispheric asymmetry and to get better psychoacoustic correlates of pathological hemispheric asymmetry in ISSNHL.

Involuntary Monitoring of Sound Signals in Noise Is Reflected in the Human Auditory Evoked N1m Response

Constant sound sequencing as operationalized by repeated stimulation with tones of the same frequency has multiple effects. On the one hand, it activates mechanisms of habituation and refractoriness, which are reflected in the decrease of response amplitude of evoked responses. On the other hand, the constant sequencing acts as spectral cueing, resulting in tones being detected faster and more accurately. With the present study, by means of magnetoencephalography, we investigated the impact of repeated tone stimulation on the N1m auditory evoked fields, while listeners were distracted from the test sounds. We stimulated subjects with trains of either four tones of the same frequency, or with trains of randomly assigned frequencies. The trains were presented either in a silent or in a noisy background. In silence, the patterns of source strength decline originating from repeated stimulation suggested both, refractoriness as well as habituation as underlying mechanisms. In noise, in contrast, there was no indication of source strength decline. Furthermore, we found facilitating effects of constant sequencing regarding the detection of the single tones as indexed by a shortening of N1m latency. We interpret our findings as a correlate of a bottom-up mechanism that is constantly monitoring the incoming auditory information, even when voluntary attention is directed to a different modality.

Auditory evoked magnetic fields in patients with absent brainstem responses due to auditory neuropathy with optic atrophy

ObjectiveTo examine whether auditory evoked fields (AEFs) can be used to objectively evaluate hearing in patients with absent auditory brainstem responses (ABRs) due to auditory neuropathy. MethodsSubjects were 3 patients with auditory neuropathy, 1 male aged 29years and 2 females aged 18 and 27years, with absence of click evoked ABRs for bilateral ear stimuli at a level of 105dB nHL. All patients also had optic atrophy. AEFs were measured with a helmet-shaped magnetoencephalography system for 2.0kHz tone bursts of 60ms duration to the unilateral ear. ResultsBihemispherical AEF responses were clearly recorded in all three patients for either left or right ear stimulus. Although the latencies of N100m were severely prolonged and amplitudes were considerably decreased compared to the normal range of N100m responses in our facilities, N100m latency of AEF was shorter in the contralateral hemisphere to the stimulated ear, as usually found in normal subjects, despite the abnormal delay in N100m latency in all conditions. ConclusionsPresence and abnormality of auditory cortical responses can be evaluated by AEFs in patients with auditory neuropathy even under null responses in ABRs. SignificanceAEFs are useful to evaluate residual hearing in patients with auditory neuropathy.

Bottom-up driven involuntary attention modulates auditory signal in noise processing

BackgroundAuditory evoked responses can be modulated by both the sequencing and the signal-to-noise ratio of auditory stimuli. Constant sequencing as well as intense masking sounds basically lead to N1m response amplitude reduction. However, the interaction between these two factors has not been investigated so far. Here, we presented subjects tone stimuli of different frequencies, which were either concatenated in blocks of constant frequency or in blocks of randomly changing frequencies. The tones were presented either in silence or together with broad-band noises of varying levels.ResultsIn silence, tones presented with random sequencing elicited a larger N1m response than tones presented with constant sequencing. With increasing noise level, this difference decreased and even vanished in the condition where noise intensity exceeded the tone intensity by 10 dB. Furthermore, under noisy conditions, the N1m latency was shorter in the constant sequencing condition compared to the random sequencing condition.ConclusionsBesides the well-known neural habituation mechanisms, bottom-up driven attention plays an important role during auditory processing in noisy environments. This bottom-up driven attention would allow us to track a certain auditory signal in noisy situations without voluntarily paying attention to the auditory modality.

The effects of pitch and pitch strength on an auditory-evoked N1m

The aim of this paper was to determine whether the latency and/or amplitude of the N1m deflection of the auditory-evoked magnetic fields are influenced by the delay and number of iterations of iterated rippled noise, which are related to pitch and pitch strength, respectively. The results indicate that the N1m amplitude decreased sharply for delays between 16 and 32 ms, suggesting that the N1m amplitude reflects the lower limit of the audible pitch range. The N1m latency increases with increasing delay of up to 8-16 ms and then decreases again for delays longer than 16 ms. The behavior of the latency may reflect the balance between the pitch-related component of the N1m and a specific pitch-unrelated component.

Cortical sensitivity to periodicity of speech sounds

Previous non-invasive brain research has reported auditory cortical sensitivity to periodicity as reflected by larger and more anterior responses to periodic than to aperiodic vowels. The current study investigated whether there is a lower fundamental frequency (F0) limit for this effect. Auditory evoked fields (AEFs) elicited by natural-sounding 400 ms periodic and aperiodic vowel stimuli were measured with magnetoencephalography. Vowel F0 ranged from normal male speech (113 Hz) to exceptionally low values (9 Hz). Both the auditory N1m and sustained fields were larger in amplitude for periodic than for aperiodic vowels. The AEF sources for periodic vowels were also anterior to those for the aperiodic vowels. Importantly, the AEF amplitudes and locations were unaffected by the F0 decrement of the periodic vowels. However, the N1m latency increased monotonically as F0 was decreased down to 19 Hz, below which this trend broke down. Also, a cascade of transient N1m-like responses was observed in the lowest F0 condition. Thus, the auditory system seems capable of extracting the periodicity even from very low F0 vowels. The behavior of the N1m latency and the emergence of a response cascade at very low F0 values may reflect the lower limit of pitch perception.

Latency variation of auditory N1m responses to vocal and nonvocal sounds

To investigate the temporal aspect of timbre processing, we recorded auditory-evoked neuromagnetic responses to periodic complex sounds, which were matched in all acoustic parameters except for two fundamental frequencies (F0s) and 12 spectral envelopes of vocal and nonvocal categories. Only for nonvocal sounds, a significant difference in N1m latency for F0 was detected in both hemispheres. A significant difference among stimuli was detected in both hemispheres for vocal and linear sounds, whereas only in the right hemisphere for instrumental sounds. Moreover, the results of paired comparison among F0s revealed that not only the vocal sounds but also some of the nonvocal sounds were F0-independent. This latency independence may be attributed to the relatively high power in the higher frequency spectrum.

Delayed N100m Latency in Focal Epilepsy Associated With Spike Dipoles at the Primary Auditory Cortex

Using magnetoencephalography (MEG), auditory evoked magnetic N100m were measured in patients with focal epilepsy and the influence of focal interictal epileptic spikes on primary auditory cortex (PAC) was evaluated. Spontaneous cerebral magnetic fields and auditory evoked magnetic fields were recorded in 40 epileptic patients and 9 healthy volunteers using MEG and latency of N100m in the bilateral hemisphere, and the distribution of epileptic spike dipoles were measured. Depending on the presence of structural lesions and the localization of spike dipoles, the patients were divided into groups as follows: group I, patients with structural lesions in PAC; group II, patients without structural lesions and with spike dipoles in PAC; and group III, patients with neither structural lesions nor spike dipoles in PAC. Nine healthy volunteers were recruited and evaluated as control group. Compared with group III and the control group, N100m latencies in groups I and II were significantly delayed. A delay in N100m latency was found not only among patients with structural lesions in PAC, but also among patients demonstrating cluster of epileptic spike dipoles in PAC. This finding indicates that the presence of epileptic spikes may influence the mechanism of processing auditory information in PAC.

Auditory cortical development charted by transient and 40-Hz steady-state responses in typical children and in Down syndrome

Abstract We are charting neocortical development in typical children and in children with Down syndrome (DS) using evoked transient and 40-Hz steady-state fields (SSFs) which localize to the region of A2 and A1 respectively, in the adult brain. Transient responses contrasted between cohorts aged 5–8 and 11–18 years showed declining P1m and increasing N1m amplitude in typical children (RMS N1m/P1m ratio increasing from 0.97 to 5.91 between the age groups), and decreasing P1m and N1m latency. Neither component changed appreciably with age in DS, although P1m latency decreased. SSF amplitude increased by a factor of 2.3 with age in control children and phase coherence by 2.0, pointing to a developmental effect putatively in A1. Neither SSF amplitude nor phase coherence showed a strong developmental trend in DS. Hearing thresholds did not differ between DS and typical children, implicating central rather than peripheral mechanisms underlying group differences.

Cortical activities evoked by air- and bone-conducted sounds with frequency variations in an audible to ultrasonic range

Abstract Few have reported the activities of auditory cortices to high-frequency sounds over 5000 Hz; though several studies have reported that bone-conducted ultrasounds (BCUs) are perceived even by those who are profoundly sensorineural deaf. Brain magnetic fields evoked by air- and bone-conducted sounds with frequency variations in an audible to ultrasonic range were recorded to clarify differences of perception mechanisms between (i) low- and high-frequency sounds, (ii) air- and bone-conducted sounds, and (iii) BCU and 12-kHz air-conducted sound, which had almost same pitch and loudness as BCU. Auditory-evoked magnetic fields evoked by air-conducted audible sounds (ACs; 500–16,000 Hz), bone-conducted audible sounds (BCs; 500–16,000 Hz), and a BCU (30,000 Hz) were measured and following results were obtained; (1) for all stimuli, substantial N1m responses were observed and equivalent current dipoles (ECDs) were localized in the Heschl's gyrus or the planum temporale. (2) Generally, the latencies increased and the ECD moments decreased as the frequency increased. (3) ACs and BCs produced by the same frequency sounds showed no differences in N1m latency and ECD moment below 8000 Hz; on the other hand, BCs showed larger latencies and smaller ECD moments than ACs over 12,000 Hz. (4) BCUs showed a larger latency and smaller ECD moments, and more posterior and lateral location than all ACs and BCs. Especially, BCU was different from 12-kHz AC in ECD moment, latency, and source location. (5) With all kinds of stimuli, the contralateral stimuli showed faster and larger N1m than the ipsilateral stimuli. These results suggest that air- and bone-conducted sounds are processed similarly below 8000 Hz, but high-frequency bone-conducted sounds over 12,000 Hz are processed differently. Considering the previous reports, the differences in the perception mechanisms possibly exists in the inner ear.

Effects of regularity, familiarity and congruity of stimuli on auditory and visually evoked magnetic fields

The auditory evoked field (AEF) component N100m represents the most prominent and stable peak of the AEF, and its alterations in patients with schizophrenia are an extensive topic of neuropsychiatric research. In our current study, the degree of N100m habituation was investigated in 20 male schizophrenics and 19 healthy male controls. Participants were stimulated monaurally with 270 trials of 1000 Hz tones separated by an interstimulus interval between 800–1800 ms. The trial sample of the bilaterally recorded AEF was separated into three consecutive blocks of 90 trials and these blocks were compared with each other. The mean global field power (MGFP) of the N100m decreased on average 9.1% from the first to the third trial block, while the N100m latency was increasing. The analyses of the influence of habituation revealed a systematic change of dipole location in inferior–superior direction, mainly in the left hemisphere. This habituation effect was found to be the same for both groups. The groups also did not differ in the N100m latency increase and MGFP decrease, except for one parameter. The right-hemispheric MGFP decrease from the first to second block was found to be more pronounced in patients compared to controls. However, this difference was related to medication with clozapine. Overall, the habituation behaviour of the N100m seems to be undisturbed in schizophrenic patients.

心因性難聴患者における聴性誘発磁場Ｎ１００ｍの所見について

We recorded the auditory-evoked fields in five patients with psychogenic hearing impairment and ten healthy controls. The maximum N100m peak amplitude and latency were measured under 1000 and 2000-Hz tone burst stimuli in each ear. The mean N100m amplitude in the patients was smaller than that in the controls. Especially, regardless of the side of stimulation, the mean amplitude in the left-hemisphere was significantly smaller in the patients than in the controls, except for the 2000-Hz stimulus condition in the left ear. There was no significant difference in the latency of the N100m peak between patients and controls. We attribute the findings of attenuation of the N100m amplitude to the peculiar auditory perception in patients with psychogenic hearing impairment. Concerning the cause of this finding, we suggest two possible mechanisms: inhibitory auditory processing and attention deficit.

The effect of center frequency and bandwidth on the auditory evoked magnetic field

Auditory evoked magnetic fields in relation to the center frequency of sound with a certain bandwidth were examined by magnetoencephalography (MEG). Octave band, 1/3 octave band, and 130 Hz bandwidth noises were used as the sound stimuli. All signals were presented at 60 dB SPL. The stimulus duration was 500 ms, with rise and fall ramps of 10 ms. Ten normal-hearing subjects took part in the study. Auditory evoked fields were recorded using a 122 channel whole-head magnetometer in a magnetically shielded room. The latencies, source strengths and coordinates of the N1m wave, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, were analyzed. The results demonstrated that the middle frequency range had shorter N1m latencies and larger N1m amplitudes, and that the lower and higher frequency stimuli had relatively delayed N1m latencies and decreased N1m amplitudes. The N1m amplitudes correlated well to the loudness values in the frequency ranges between 250 and 2000 Hz. The source locations of N1m did not reveal any systematic changes related to the center frequency and bandwidth.

Auditory evoked fields to variations of interaural time delay

Auditory motion can be simulated by presenting binaural sounds with time-varying interaural time delays. Human cortical responses to the rate of auditory motion were studied by recording auditory evoked magnetic fields with a 122-channel whole-head magnetometer. Auditory motion from central to right and then to central was produced by varying interaural time differences between ears. The results showed that the N1m latencies and amplitudes were not affected by the fluctuation of interaural time delay; however, the peak amplitude of P2m significantly increased as a function of fluctuation of the interaural time delay.

Perceptual categorization of sound spectral envelopes reflected in auditory-evoked N1m

Magnetic responses to periodic complex sounds with equivalent acoustic parameters except for two different fundamental frequencies (F0) and 12 different spectral envelopes of vocal, instrumental, and linear shapes were recorded to determine the cortical representation of timbre categorization in humans. Responses at approximately 100 ms (N1m) to vocal and instrumental (nonlinear) sounds were localized significantly anterior to linear sound responses. N1m source strength for nonlinear sounds was significantly larger than that for linear sounds, and this difference was more marked in the left hemisphere than in the right. N1m peak latency only for vocal sounds was not affected by F0. Perceptual categorization was reflected in N1m source strength and location (linear or nonlinear), and in N1m latency (vocal or nonvocal).

Measurement of brain magnetic fields evoked by bone-conducted ultrasounds: effect of frequencies

Several studies have reported that high-frequency sounds of more than 20,000 Hz can be perceived by the profoundly sensorineural deaf subjects, as well as normal-hearing, through bone conduction. Although the mechanisms of how bone-conducted ultrasound (BCU) is perceived remain unclear, several characteristics that differ from air-conducted audible sounds are reported; for example, the pitch of BCU is independent of the frequency. In this study, the effects of BCU frequency on the activities of auditory cortex were investigated by magnetoencephalography (MEG). Auditory-evoked magnetic fields evoked by four kinds of BCU stimuli, 22,000, 27,000, 32,000, and 37,000 Hz tone bursts, were measured, and equivalent current dipoles (ECDs) of N1m were estimated. No significant differences were observed among the four kinds of BCU stimuli, not only in pitch, but also in N1m latency, ECD moment, and ECD location; whereas obvious differences were observed between the air-conducted sounds and BCUs. These results suggest that the mechanisms for BCU perception are different from those for air-conducted audible sounds.