Late Auditory Evoked Potentials Research Articles

Intensity discrimination and neural representation of a masked tone in the presence of three types of masking release.

Hearing ability is usually evaluated by assessing the lowest detectable intensity of a target sound, commonly referred to as a detection threshold. Detection thresholds of a masked signal are dependent on various auditory cues, such as the comodulation of the masking noise, interaural differences in phase, and temporal context. However, considering that communication in everyday life happens at sound intensities well above the detection threshold, the relevance of these cues for communication in complex acoustical environments is unclear. Here, we investigated the effect of three cues on the perception and neural representation of a signal in noise at supra-threshold levels. First, we measured the decrease in detection thresholds produced by three cues, referred to as masking release. Then, we measured just-noticeable difference in intensity (intensity JND) to quantify the perception of the target signal at supra-threshold levels. Lastly, we recorded late auditory evoked potentials (LAEPs) with electroencephalography (EEG) as a physiological correlate of the target signal in noise at supra-threshold levels. The results showed that the overall masking release can be up to around 20 dB with a combination of these three cues. At the same supra-threshold levels, intensity JND was modulated by the masking release and differed across conditions. The estimated perception of the target signal in noise was enhanced by auditory cues accordingly, however, it did not differ across conditions when the target tone level was above 70 dB SPL. For the LAEPs, the P2 component was more closely linked to the masked threshold and the intensity discrimination than the N1 component. The results indicate that masking release affects the intensity discrimination of a masked target tone at supra-threshold levels, especially when the physical signal-to-noise is low, but plays a less significant role at high signal-to-noise ratios.

A basic identification of late auditory evoked potentials at infrasound frequencies: Support via neural network–based signal processing

Concerns about potential health risks from infrasound exposure require objective investigation methods for the perception of infrasound by humans. Neural-network methods were applied to identify weak infrasound evoked potentials and to investigate the efficacy of these techniques. Two simple networks – a fully connected three-layer feed-forward network and a two-layer autoencoder – were designed for the analysis of electroencephalography (EEG) data recorded in response to infrasound stimuli presented. Late auditory evoked potentials (LAEPs) were detected and correlation factors between the target and the output of the networks were determined to assess the differentiation ability of the two networks. Both networks were able to differentiate infrasound evoked potentials from noise but showed different performance levels with respect to a differentiation threshold. The results can be applied to objectively identify perception events by infrasound in humans.

Systematic review and meta-analysis of late auditory evoked potentials as a candidate biomarker in the assessment of tinnitus.

Subjective tinnitus, the perception of sound in the absence of any sound source, is routinely assessed using questionnaires. The subjective nature of these tools hampers objective evaluation of tinnitus presence, severity and treatment effects. Late auditory evoked potentials (LAEPs) might be considered as a potential biomarker for assessing tinnitus complaints. Using a multivariate meta-analytic model including data from twenty-one studies, we determined the LAEP components differing systematically between tinnitus patients and controls. Results from this model indicate that amplitude of the P300 component is lower in tinnitus patients (standardized mean difference (SMD) = -0.83, p < 0.01), while latency of this component is abnormally prolonged in this population (SMD = 0.97, p < 0.01). No other investigated LAEP components were found to differ between tinnitus and non-tinnitus subjects. Additional sensitivity analyses regarding differences in experimental conditions confirmed the robustness of these results. Differences in age and hearing levels between the two experimental groups might have a considerable impact on LAEP outcomes and should be carefully considered in future studies. Although we established consistent differences in the P300 component between tinnitus patients and controls, we could not identify any evidence that this component might covary with tinnitus severity. We conclude that out of several commonly assessed LAEP components, only the P300 can be considered as a potential biomarker for subjective tinnitus, although more research is needed to determine its relationship with subjective tinnitus measures. Future trials investigating experimental tinnitus therapies should consider including P300 measurements in the evaluation of treatment effect.

Effects of Acoustic Paired Associative Stimulation on Late Auditory Evoked Potentials

Paired associative stimulation (PAS), a form of non-invasive cortical stimulation pairing transcranial magnetic stimulation (TMS) with a peripheral sensory stimulus, has been shown to induce neuroplastic effects in the human motor, somatosensory and auditory cortex. The current study investigated the effects of acoustic PAS on late auditory evoked potentials (LAEP) and the influence of tone duration and placebo stimulation. In two experiments, 18 participants underwent a PAS with a 4 kHz paired tone of 400 ms duration using 200 pairs of stimuli (TMS-pulse over the left auditory cortex 45 ms after tone-onset) presented at 0.1 Hz. In Experiment 1 this protocol was contrasted with a protocol using a short paired tone of 23 ms duration (PAS-23 ms vs. PAS-400 ms). In Experiment 2 this PAS protocol was contrasted with sham stimulation (PAS-400 ms-sham vs. PAS-400 ms). Before and after PAS, LAEP were recorded for tones of 4 kHz (same carrier frequency as the paired tone) and 1 kHz as control tone. In Experiment 1, there was a significant difference between LAEP amplitudes of the 4 kHz tone after PAS-23 ms and PAS-400 ms with higher LAEP amplitudes after PAS-23 ms. Before both conditions, no difference could be detected. In Experiment 2 we observed a significant overall decrease in LAEP amplitudes pre to post PAS. Unspecific decreases of LAEP following PAS with a long paired tone (PAS-400 ms) might be related to habituation effects due to repeated presentation of sound stimuli which are not evident for PAS with a short paired tone (PAS-23 ms). Interpreting this result using the concept of temporal integration time allows us to discuss it in the context of spike-timing dependent plasticity.

Longitudinal auditory learning facilitates auditory cognition as revealed by microstate analysis

The current study investigates cognitive processes as reflected in late auditory-evoked potentials as a function of longitudinal auditory learning. A normal hearing adult sample (n=15) performed an active oddball task at three consecutive time points (TPs) arranged at two week intervals, and during which EEG was recorded. The stimuli comprised of syllables consisting of a natural fricative (/sh/,/s/,/f/) embedded between two /a/ sounds, as well as morphed transitions of the two syllables that served as deviants. Perceptual and cognitive modulations as reflected in the onset and the mean global field power (GFP) of N2b- and P3b-related microstates across four weeks were investigated. We found that the onset of P3b-like microstates, but not N2b-like microstates decreased across TPs, more strongly for difficult deviants leading to similar onsets for difficult and easy stimuli after repeated exposure. The mean GFP of all N2b-like and P3b-like microstates increased more in spectrally strong deviants compared to weak deviants, leading to a distinctive activation for each stimulus after learning. Our results indicate that longitudinal training of auditory-related cognitive mechanisms such as stimulus categorization, attention and memory updating processes are an indispensable part of successful auditory learning. This suggests that future studies should focus on the potential benefits of cognitive processes in auditory training.

Electrophysiological and psychophysical asymmetries in sensitivity to interaural correlation gaps and implications for binaural integration time

Brief deviations of interaural correlation (IAC) can provide valuable cues for detection, segregation and localization of acoustic signals. This study investigated the processing of such “binaural gaps” in continuously running noise (100–2000 Hz), in comparison to silent “monaural gaps”, by measuring late auditory evoked potentials (LAEPs) and perceptual thresholds with novel, iteratively optimized stimuli. Mean perceptual binaural gap duration thresholds exhibited a major asymmetry: they were substantially shorter for uncorrelated gaps in correlated and anticorrelated reference noise (1.75 ms and 4.1 ms) than for correlated and anticorrelated gaps in uncorrelated reference noise (26.5 ms and 39.0 ms). The thresholds also showed a minor asymmetry: they were shorter in the positive than in the negative IAC range. The mean behavioral threshold for monaural gaps was 5.5 ms. For all five gap types, the amplitude of LAEP components N1 and P2 increased linearly with the logarithm of gap duration. While perceptual and electrophysiological thresholds matched for monaural gaps, LAEP thresholds were about twice as long as perceptual thresholds for uncorrelated gaps, but half as long for correlated and anticorrelated gaps. Nevertheless, LAEP thresholds showed the same asymmetries as perceptual thresholds. For gap durations below 30 ms, LAEPs were dominated by the processing of the leading edge of a gap. For longer gap durations, in contrast, both the leading and the lagging edge of a gap contributed to the evoked response. Formulae for the equivalent rectangular duration (ERD) of the binaural system's temporal window were derived for three common window shapes. The psychophysical ERD was 68 ms for diotic and about 40 ms for anti- and uncorrelated noise. After a nonlinear Z-transform of the stimulus IAC prior to temporal integration, ERDs were about 10 ms for reference correlations of ±1 and 80 ms for uncorrelated reference. Hence, a physiologically motivated peripheral nonlinearity changed the rank order of ERDs across experimental conditions in a plausible manner.

Simultaneous acquisition of high-rate early, middle, and late auditory evoked potentials.

Auditory evoked potentials (AEPs) are typically acquired at rates that facilitate their study as segregated by epochs relative to stimulus onset: early (ABR, 1.5-15 ms), middle (MLR, 15-60 ms), and late (LAEP, ≥60 ms) potentials. In particular, late AEPs are often acquired with stimulus repetition rates between 0.1 Hz and 1 Hz, and are bandpass filtered to contain information only within 1-30 Hz. These low repetition rates, filtering and low SNRs eliminate much of the potential contributions of the early and middle-latency responses in AEP recordings. This study aims to demonstrate a method for acquiring whole-AEP responses at higher stimulus repetition rates of 0.5 Hz to 10 Hz, by utilizing the Continuous Loop Averaging Deconvolution (CLAD) method, increasing the bandwidth of the recordings to 1-300 Hz to include early components, and using short-duration chirps to increase synchronous firing of the cochlear and auditory pathway neurons. Such a method may facilitate diagnostic or functional assessment of single AEP recordings for detection, identification, or evaluation of early, middle and late components of auditory responses.

Mechanisms of adaptation in human auditory cortex

This study investigates the temporal properties of adaptation in the late auditory-evoked potentials in humans. The results are used to make inferences about the mechanisms of adaptation in human auditory cortex. The first experiment measured adaptation by single adapters as a combined function of the adapter duration and the stimulus onset asynchrony (SOA) and interstimulus interval (ISI) between the adapter and the adapted sound ("probe"). The results showed recovery from adaptation with increasing ISI, as would be expected, but buildup of adaptation with increasing adapter duration and thus SOA. This suggests that adaptation in auditory cortex is caused by the ongoing, rather than the onset, response to the adapter. Quantitative modeling indicated that the rate of buildup of adaptation is almost an order of magnitude faster than the recovery rate of adaptation. The recovery rate suggests that cortical adaptation is caused by synaptic depression and slow afterhyperpolarization. The P2 was more strongly affected by adaptation than the N1, suggesting that the two deflections originate from different cortical generators. In the second experiment, the single adapters were replaced by trains of two or four identical adapters. The results indicated that adaptation decays faster after repeated presentation of the adapter. This increase in the recovery rate of adaptation might contribute to the elicitation of the auditory mismatch negativity response. It may be caused by top-down feedback or by local processes such as the buildup of residual Ca(2+) within presynaptic neurons.

Cochlear implant artifact attenuation in late auditory evoked potentials: A single channel approach

Recent evidence suggests that late auditory evoked potentials (LAEP) provide a useful objective metric of performance in cochlear implant (CI) subjects. However, the CI produces a large electrical artifact that contaminates LAEP recordings and confounds their interpretation. Independent component analysis (ICA) has been used in combination with multi-channel recordings to effectively remove the artifact. The applicability of the ICA approach is limited when only single channel data are needed or available, as is often the case in both clinical and research settings. Here we developed a single-channel, high sample rate (125 kHz), and high bandwidth (0–100 kHz) acquisition system to reduce the CI stimulation artifact. We identified two different artifacts in the recording: 1) a high frequency artifact reflecting the stimulation pulse rate, and 2) a direct current (DC, or pedestal) artifact that showed a non-linear time varying relationship to pulse amplitude. This relationship was well described by a bivariate polynomial. The high frequency artifact was completely attenuated by a 35 Hz low-pass filter for all subjects (n = 22). The DC artifact could be caused by an impedance mismatch. For 27% of subjects tested, no DC artifact was observed when electrode impedances were balanced to within 1 kΩ. For the remaining 73% of subjects, the pulse amplitude was used to estimate and then attenuate the DC artifact. Where measurements of pulse amplitude were not available (as with standard low sample rate systems), the DC artifact could be estimated from the stimulus envelope. The present artifact removal approach allows accurate measurement of LAEPs from CI subjects from single channel recordings, increasing their feasibility and utility as an accessible objective measure of CI function.

Effectiveness of steady versus varied-color/varied-pattern visual tasks during acquisition of late auditory evoked potentials

Instructions for late auditory evoked potential (LAEP) testing include a need for the subject to remain alert (not go to sleep). Previous studies show an inverse relationship between alertness level and waveform morphology. Thus, a need exists to maintain alertness during LAEP testing. If not maintained, a wide range of alertness, and thus waveform morphology, may exist from one run to the next. Therefore, if alertness level is not controlled, any variations in waveform morphology may be due to variations in alertness rather than auditory system integrity. Previous investigators have implemented visual tasks consisting of still or action images in an attempt to maintain alertness. In these visual tasks, a subject is typically instructed to attend to a video screen during LAEP testing. This project investigated the effectiveness of two visual task screens: unvaried blue with no pattern, versus varied colors-patterns occurring in 1-3 second random intervals. LAEPs were gathered on twenty-five young adult subjects who were instructed to attend to a video display of one of the screens during LAEP testing. Six replicates were obtained for each screen in counter-balanced order. Results showed no significant (p&amp;gt;.05) differences in mean P1 or P2 latency or amplitude for the two screens.

Feasibility of an objective electrophysiological loudness scaling: A kernel-based novelty detection approach

The objective of our research is to structure a foundation for an electrophysiological loudness scaling measurement, in particular to estimate an uncomfortable loudness (UCL) level by using the hybrid wavelet-kernel novelty detection (HWND). Late auditory evoked potentials (LAEPs) were obtained from 20 normal hearing adults. These LAEPs were stimulated by 4 intensity levels (60 decibel (dB) sound pressure level (SPL), 70 dB SPL, 80 dB SPL, and 90 dB SPL). We have extracted the habituation correlates in LAEPs by using HWND. For this, we employed a lattice structure-based wavelet frame decompositions for feature extraction combined with a kernel-based novelty detector. The group results showed that the habituation correlates degrees, i.e., relative changes within the sweep sequences, were significantly different among 60 dB SPL, 70 dB SPL, 80 dB SPL, and 90 dB SPL stimulation level, independently from the intensity related amplitude information in the averaged LAEPs. At these particular intensities, 60% of the subjects show the correlation between the novelty measures and the stimulation levels resembles a loudness scaling function, in reverse. In this paper, we have found a correlation in between the novelty measures and loudness perception as well. We have found that high ranges of loudness levels such as loud, upper level and too loud show generally 4.88% of novelty measures and comfortable ranges of loudness levels, i.e., soft, comfortable but soft, comfortable loud and comfortable but loud are generally have 12.29% of novelty measures. Additionally, we demonstrated that our sweep-to-sweep basis of post processing scheme is reliable for habituation extraction and offers an advantage of reducing experimental time as the proposed scheme need less than 20% of single sweeps in comparison to the amount that are commonly used in arithmetical average for a meaningful result. We assessed the feasibility of habituation correlates for an objective loudness scaling. With respect to this first feasibility study, the presented results are promising when using the described signal processing and machine learning methodology. For the group results, the novelty measures approach is able to discriminate 60 dB, 70 dB, 80 dB and 90 dB stimulated sweeps. In addition, a correlation between the novelty measures and the subjective loudness scaling is observed. However, more loudness perception and frequency specific experiments need to be conducted to determine the UCL novelty measures threshold as well as clinically oriented studies are necessary to evaluate whether this approach might be used in the objective hearing instrument fitting procedures.

Recovery Function of the Late Auditory Evoked Potential in Cochlear Implant Users and Normal-Hearing Listeners

It has been theorized that neural recovery is related to temporal coding of speech sounds. The recovery function of cortically generated auditory evoked potentials has not been investigated in cochlear implant (CI) users. This study characterized the recovery function of the late auditory evoked potential (LAEP) using a masker-probe paradigm in postlingually deafened adult CI users and young normal-hearing (NH) listeners. A case-control study of the late auditory evoked potentials using electrophysiological technique was performed. The LAEP was evoked by 1 kHz tone bursts presented in pairs, with the first stimuli as the maskers and the second stimuli as the probes. The masker-probe intervals (MPIs) were varied at 0.7, 1, 2, 4, and 8 sec, with an interpair interval of 12 sec. Nine CI users and nine NH listeners participated in this study. The normalized amplitude from the probe response relative to the masker response was plotted as a function of the MPI to form a recovery function. The latency shift for the probe response relative to the masker response was calculated. The recovery function was approximately linear in log scale of the MPI in NH listeners, while it showed somewhat different recovery patterns with a large intersubject variability in CI users. Specifically, although the probe response was approximately 60 percent of the masker response for the MPI of 0.7 sec in both groups, the recovery function of CI users displayed a nonlinear pattern, with a steeper slope than that of NH listeners. The probe response completely recovered at the MPI of 4 sec in NH listeners and at the MPI of 2 sec in CI users. N1 and P2 latencies from probe responses were shorter than those from masker responses in NH listeners, while no latency difference was found between probe responses and masker responses in CI users. Our interpretation of these findings is that the faster recovery of the LAEP in CI users is related to abnormal adaptation mechanisms and a less prominent role of the components with longer latencies in the LAEP of CI users. Other mechanisms such as the compromised inhibitory regulation in the auditory system and the aging effect in CI users might also play a role. More research needs to be done to determine whether the slope of the LAEP recovery function is correlated with speech-perception performance.

Electrophysiological and psychophysical asymmetries in sensitivity to interaural correlation steps

The binaural auditory system’s sensitivity to changes in the interaural cross correlation (IAC), as an indicator for the perceived spatial diffuseness of a sound, is of major importance for the ability to distinguish concurrent sound sources. In this article, we present electroencephalographical and corresponding psychophysical experiments with stepwise transitions of the IAC in continuously running noise. Both the transient and sustained brain response, display electrophysiological correlates of specific binaural processing in humans. The transient late auditory evoked potentials (LAEP) systematically depend on the size of the IAC transition, the reference correlation preceding the transition, the direction of the transition and on unspecific context information from the stimulus sequence. The psychophysical and electrophysiological data are characterized by two asymmetries. (1) Major asymmetry: for reference correlations of + 1 and - 1 , psychoacoustical thresholds are comparatively lower, and the peak-to-peak-amplitudes of LAEP are larger than for a reference correlation of zero. (2) Minor asymmetry: for IAC transitions in the positive parameter range, perceptual thresholds are slightly better and peak-to-peak amplitudes are larger than in the negative range. In all experimental conditions, LAEP amplitudes are linearly related to the dB scaled power ratio of correlated ( N 0 ) versus anticorrelated ( N π ) signal components. The voltage gain of LAEP per dB( N 0 / N π ) closely corresponds to a constant perceptual distance between two correlations. We therefore suggest that activity in the auditory cortex and perceptual IAC sensitivity are better represented by the dB-scaled N 0 / N π power ratio than by the normalized IAC itself.

Comparing the habituation of late auditory evoked potentials to loud and soft sound

The objective fitting of hearing aids and cochlear implants remains a challenge. In particular, the determination of whether sound is perceived as too loud or comfortable represents an unsolved problem in noncooperative patients. In a first step of an ongoing study, we assess the feasibility of habituation correlates in late auditory evoked potentials (LAEPs) to discriminate between a soft sound (SS) of 50 dB SPL and a loud sound (LS) of 100 dB SPL. We applied a new sweep-to-sweep time-scale coherence measure to analyse the habituation in LAEPs, i.e., relative changes within sweep sequences. From the comparison between both stimulation levels, a total discrimination of responses to SS and LS in the individual normal hearing subject was possible. As just relative changes in SS and LS sweep sequences were considered, purely exogenously driven morphological alternations in the responses such as intensity related amplitude and latency changes were excluded from the analysis. It is concluded that the proposed method allows for the reliable detection of auditory habituation and differentiation of SS from LS. The proposed scheme might provide an electrophysiological measurement and signal processing framework for the objective detection of the most comfortable loudness level and can be used in further, more clinically oriented studies.

Electrophysiological and behavioral correlates of polymorphisms in the transcription factor AP-2β coding gene

Transcription factor AP-2beta may influence brain monoaminergic systems by regulating target genes. Several monoaminergic genes, including the serotonin transporter gene, have AP-2beta binding sites. Late auditory-evoked potentials (P1, N1/P2) and impulsiveness-related personality traits are correlated, and both are modulated by monoaminergic neurotransmission. The present study assesses the impact of two AP-2beta polymorphisms (VNTRs within intron 1 and 2) together with the serotonin transporter polymorphism 5-HTTLPR on late auditory-evoked potentials and personality for the first time. EEG was recorded from 91 male subjects at central electrode positions while tones of six intensity levels were presented. Additionally, subjects completed personality questionnaires. Both AP-2beta polymorphisms revealed significant main effects on P1, and haplotype analysis confirmed the contribution of both AP-2beta-polymorphisms. Additionally, AP-2beta and 5-HTTLPR showed interactions with respect to P1. 5-HTTLPR revealed a main effect on N1/P2 but not P1. Impulsiveness showed an association with intron 1 VNTR. The results are discussed with respect to differential impact of AP-2beta polymorphisms and 5-HTTLPR on the monoaminergic systems. The findings promote replication in a larger sample and suggest a potential usefulness of AP-2beta polymorphisms in explaining or predicting central nervous diseases, drug effects and side effects.

The role of the temporal pole in auditory processing

ABSTRACT Experiments in animals have shown that the temporal pole and the amygdala are involved in auditory processing. Comparable data are scarce in humans. It is only known that after temporal lobectomy, hearing may be impaired and dichotic listening scores reduced on the ear contralateral to the operated temporal lobe. Middle‐latency auditory evoked potentials (MLAEPs) and late auditory evoked potentials (LAEPs) have been recorded in 14 patients before and after temporal lobectomy for the treatment of drug‐resistant temporal lobe epilepsy. The Na and Pa components of MLAEPs were significantly delayed and the Pa component amplitude reduced before and after surgery as compared to a group of 21 healthy subjects. Data in pre‐ and postoperative period were not statistically different. N100 and P200 component of LAEPs were similarly altered. It is concluded that in humans the amygdala and probably the temporal pole may be involved in the process of auditory activation‐inhibition. The possible role of auditory processing impairment in cognitive deficits in TLE patients can also be questioned.

Loudness perception and late auditory evoked potentials in adult cochlear implant users

In clinical routine the adjustment of speech processors in cochlear implant users is based on the patients' subjective statements about the loudness of specific electrical stimuli. From hearing patients it is known that the latencies and amplitudes of late auditory evoked potentials (LAEP) which are generated within the auditory cortex correlate with the loudness perception of acoustical stimuli. The aim of this study was to investigate the correlation between LAEP and loudness perception in adult cochlear implant users. We investigated 8 adult subjects who had been provided with a 22 electrode Cochlear Implant (nucleus CI24M) at least 6 months prior to the investigation. All subjects showed open speech understanding. Electrical pulse trains of 300 ms duration presented at a single electrode served as stimuli. Electrically LAEP morphologies were similar to normal hearing subjects. In all subjects and each intracochlear electrode position LAEP were well identifiable down to low loudness sensations. Both amplitudes and latencies depended on the loudness perception. The best correlation was observed for the N1 deflection. The results show that LAEP can be used for estimation of both hearing thresholds and most comfortable levels.

The development of auditory evoked dipole source activity from childhood to adulthood

Objective: Multi-channel recordings show that observed developmental changes of late auditory evoked potentials (LAEP) depend on the location of the scalp electrode. These findings suggest that different LAEP generators have a distinct developmental course. The goal of this study was to investigate the maturational process of cortical LAEP generators. Methods: Eighty-seven healthy children and adolescents with normal hearing, ages 5–16 years, and 21 adults, ages 20–30 years, participated in the study. Pure tone LAEP were recorded from 21 derivations. Dipole source analysis was performed by means of brain electric source analysis (BESA). Peak latencies and amplitudes of dipole source activity were estimated. Results: While the number, location, and direction of dipole sources were similar in children and adults, the course of their activity differed greatly. The latencies shortened and the amplitudes decreased during development. In adolescence a new component appeared in the activity of the tangential dipole, which reflects the generators in the supra-temporal plane. The variability of parameters was greater in children than in adults. Conclusions: Since the dipole source activity of LAEP in childhood differs considerably from that in adulthood, dipole source analysis could be a useful tool for studying both normal and disturbed maturation of the auditory perceptual function.

Intracerebral Sources of Human Auditory-Evoked Potentials

Evoked potentials to brief 1,000-Hz tones presented to either the left or the right ear were recorded from 30 electrodes arrayed over the head. These recordings were submitted to two different forms of source analysis: brain electric source analysis (BESA) and variable-resolution electromagnetic tomography (VARETA). Both analyses showed that the dominant intracerebral sources for the late auditory-evoked potentials (50–300 ms) were in the supratemporal plane and lateral temporal lobe contralateral to the ear of stimulation. The analyses also suggested the possibility of additional sources in the frontal lobes.

Hemispheric asymmetry of late auditory evoked response induced by pitch changes in infants: influence of sleep stages

Late auditory evoked potentials (LAEPs) have been recorded in response to a 1000 Hz standard (occurrence 80%) or a 2000 Hz deviant (occurrence 20%) tone on the left (T3) and right (T4) temporal scalp in 6-week-old full-term newborns during pure quiet or active sleep states. Sleep states were permanently controlled by polygraphic recording including EEG, EOG, EMG, EKG and respiratory movements. During quiet sleep LAEPs consisted of a clear polygraphic response: N1-P2-N2. Mean latencies ranges in T3 and T4 were: N1 = 28–70 ms; P2 = 343–407 ms;N2 = 966–1178 ms; and P3 = 1461–1492 ms. During active sleep LAEPs consisted of a N1-P2-N2 response. Mean latency ranges on T3 and T4 were: N1 = 36–79 ms; P2 =278–304 ms; N2 = 555–620 ms. N2 latency was significantly shorter in AS than in QS. Amplitude of the N1-P2-N2 complex was significantly lower during active sleep. In response to standard stimuli, mean amplitudes and latencies of the LAEP were similar on T3 and T4 during active or quiet sleep states. In response to deviant stimuli mean amplitude of the N1-P2-N2 complex was significantly higher and mean latencies of N1 and N2 were significantly shorter on T3 during quiet sleep. No significant difference was observed during active sleep. These results confirm that sleep stages have a considerable influence on cortical auditory pathways. The auditory message is amplified during quiet sleep and inhibited during active sleep. Therefore sleep states need to be controlled to analyze LAEPs in young children. Furthermore our results show that unexpected auditory stimuli are differentiated in the temporal area of the left hemisphere of 6-week-old infants. This represents a functional correlate of the known hemispherical asymmetry in the speech region of the temporal cortex.