Age differences of event-related potentials in the perception of successive and spatial components of auditory information

The perception of spatial and successive contexts of auditory information develops during child ontogeny. We compared event-related potentials (ERPs) recorded in 5- to 6-year-old children (N = 15) and adults (N = 15) in response to a digital series with omitted digits to explore age differences in the perception of successive auditory information. In addition, ERPs in response to the sound of a falling drop presented binaurally were obtained to examine the spatial content of auditory information. The ERPs obtained from the omitted digits significantly differed in the amplitude and latency of the N200 and P300 components between adults and children, which supports the hypothesis that the perception of a successive auditory structure is less automatic in children compared to adults. Although no significant differences were found in adults, the sound of a falling drop presented to the left ears of children elicited ERPs with earlier latencies and higher amplitudes of the P300 and N400 components in the right temporal area. Stimulation of the right ear caused an increasing amplitude of the N100 component in children. Thus, the observed differences in the auditory ERPs of children and adults reflect developmental changes in the perception of spatial and successive auditory information.     

Temporal Sequence of Visuo-Auditory Interaction in Multiple Areas of the Guinea Pig Visual Cortex

Recent studies in humans and monkeys have reported that acoustic stimulation influences visual responses in the primary visual cortex (V1). Such influences can be generated in V1, either by direct auditory projections or by feedback projections from extrastriate cortices. To test these hypotheses, cortical activities were recorded using optical imaging at a high spatiotemporal resolution from multiple areas of the guinea pig visual cortex, to visual and/or acoustic stimulations. Visuo-auditory interactions were evaluated according to differences between responses evoked by combined auditory and visual stimulation, and the sum of responses evoked by separate visual and auditory stimulations. Simultaneous presentation of visual and acoustic stimulations resulted in significant interactions in V1, which occurred earlier than in other visual areas. When acoustic stimulation preceded visual stimulation, significant visuo-auditory interactions were detected only in V1. These results suggest that V1 is a cortical origin of visuo-auditory interaction.     

Auditory Cortex Processes Variation in Our Own Speech

As we talk, we unconsciously adjust our speech to ensure it sounds the way we intend it to sound. However, because speech production involves complex motor planning and execution, no two utterances of the same sound will be exactly the same. Here, we show that auditory cortex is sensitive to natural variations in self-produced speech from utterance to utterance. We recorded event-related potentials (ERPs) from ninety-nine subjects while they uttered “ah” and while they listened to those speech sounds played back. Subjects'' utterances were sorted based on their formant deviations from the previous utterance. Typically, the N1 ERP component is suppressed during talking compared to listening. By comparing ERPs to the least and most variable utterances, we found that N1 was less suppressed to utterances that differed greatly from their preceding neighbors. In contrast, an utterance''s difference from the median formant values did not affect N1. Trial-to-trial pitch (f0) deviation and pitch difference from the median similarly did not affect N1. We discuss mechanisms that may underlie the change in N1 suppression resulting from trial-to-trial formant change. Deviant utterances require additional auditory cortical processing, suggesting that speaking-induced suppression mechanisms are optimally tuned for a specific production.     

Event-related potentials in the dorsal hippocampus of rats during an auditory discrimination paradigm

The relation of the hippocampal neuronal activity to the rat event-related potential (ERP) generation was examined during an auditory discrimination oddball paradigm. ERPs were recorded using a linearly-arranged series of electrodes chronically implanted at the skull, in the frontoparietal cortex, in the CA1 and CA3 regions of the dorsal hippocampus and in the thalamus. The target tone elicited N40, P100, N200, and P450 at the skull electrode. The non-target tone, on the other hand, prominently evoked only the P100 component. At the intracranial electrodes, the ERP amplitude at the latency of the skull P450 was significantly greater in the CA3 region than that at other recording sites, although a phase reversal was not observed. The results indicate that the P450 of the rat may correspond to the human P3, and that the neuronal activity in the hippocampus is involved in its generation.     

Auditory cortex basal activity modulates cochlear responses in chinchillas

Background

The auditory efferent system has unique neuroanatomical pathways that connect the cerebral cortex with sensory receptor cells. Pyramidal neurons located in layers V and VI of the primary auditory cortex constitute descending projections to the thalamus, inferior colliculus, and even directly to the superior olivary complex and to the cochlear nucleus. Efferent pathways are connected to the cochlear receptor by the olivocochlear system, which innervates outer hair cells and auditory nerve fibers. The functional role of the cortico-olivocochlear efferent system remains debated. We hypothesized that auditory cortex basal activity modulates cochlear and auditory-nerve afferent responses through the efferent system.

Methodology/Principal Findings

Cochlear microphonics (CM), auditory-nerve compound action potentials (CAP) and auditory cortex evoked potentials (ACEP) were recorded in twenty anesthetized chinchillas, before, during and after auditory cortex deactivation by two methods: lidocaine microinjections or cortical cooling with cryoloops. Auditory cortex deactivation induced a transient reduction in ACEP amplitudes in fifteen animals (deactivation experiments) and a permanent reduction in five chinchillas (lesion experiments). We found significant changes in the amplitude of CM in both types of experiments, being the most common effect a CM decrease found in fifteen animals. Concomitantly to CM amplitude changes, we found CAP increases in seven chinchillas and CAP reductions in thirteen animals. Although ACEP amplitudes were completely recovered after ninety minutes in deactivation experiments, only partial recovery was observed in the magnitudes of cochlear responses.

Conclusions/Significance

These results show that blocking ongoing auditory cortex activity modulates CM and CAP responses, demonstrating that cortico-olivocochlear circuits regulate auditory nerve and cochlear responses through a basal efferent tone. The diversity of the obtained effects suggests that there are at least two functional pathways from the auditory cortex to the cochlea.     

Event-related potential measures of attention in moderately depressed subjects

Prior research has inferred attentional changes related to depression from evidence concerning other cognitive processes. The present experiment investigated attentional changes related to depression in a more direct manner. Subjects were 32 young adults attending college. Depression was measured by self-report measures. In an auditory selective attention task similar to that of Hansen and Hillyard (1980), auditory event-related potentials(ERPs) were recorded from central (Cz) and frontal (Fz) scalp locations. Evidence for selective attention was manifest as the difference wave (Nd), which showed larger mean and peak amplitudes for the less difficult of two attention conditions. Nd was also shown to have an earlier peak latency at the Cz scalp location. However, there was no significant difference between the Depressed and Control groups as measured by the Nd wave. Significant differences were found between groups for the amplitude of the N1 peak of the ERP at the Fz scalp location. This suggests that the Depressed group differed in arousal level or sensory sensitivity from the Control group.     

Potentials evoked in human and monkey medial temporal lobe during auditory and visual oddball paradigms

Event-related potentials (ERPs) were recorded from epileptic patients with electrodes chronically implanted in the medial temporal lobe (MTL) and other intracranial locations, and from monkeys with epidural, transcortical, and MTL electrodes. For both humans and monkeys, the eliciting events consisted of trains of auditory or visual stimuli in which a random 10–20% deviated in pitch or pattern from the remaining stimuli. The distribution of ERPs elicited by the rare (oddball) stimuli in both species was similar, consisting of a P3 recorded from the scalp or cortical surface and a slightly later, but temporally overlapping, focal negativity in the hippocampus and nearby MTL structures. The similarity between the patterns of ERPs in humans and monkeys establishes the feasibility of studying the electrogenesis of P3-like activity with detailed intracranial recordings in an animal model. The data also establish that the MTL ERPs in human patients represent a normal neurophysiological process unrelated to epilepsy.     

An ERP study of temporal discrimination in rats

In this study, we examined event-related potentials (ERPs) in rats performing a timing task. The ERPs were recorded during a timing task and a control task from five regions (frontal cortex, striatum, hippocampus, thalamus, and cerebellum) that are related to time perception. In the timing task, the rats were required to judge the interval between two tones. This interval could be either 500 or 2000 ms. In the control task, only the 500 ms interval between tones was presented and only one lever was available for responses. Any difference in ERPs between the two tasks was considered to reflect the processes that are related to temporal discrimination. The frontal cortex, striatum, and thalamus yielded concurrent differences in ERPs between the two tasks. The results suggest that these regions might play an important role in temporal discrimination.     

Sparse Spectro-Temporal Receptive Fields Based on Multi-Unit and High-Gamma Responses in Human Auditory Cortex

Spectro-Temporal Receptive Fields (STRFs) were estimated from both multi-unit sorted clusters and high-gamma power responses in human auditory cortex. Intracranial electrophysiological recordings were used to measure responses to a random chord sequence of Gammatone stimuli. Traditional methods for estimating STRFs from single-unit recordings, such as spike-triggered-averages, tend to be noisy and are less robust to other response signals such as local field potentials. We present an extension to recently advanced methods for estimating STRFs from generalized linear models (GLM). A new variant of regression using regularization that penalizes non-zero coefficients is described, which results in a sparse solution. The frequency-time structure of the STRF tends toward grouping in different areas of frequency-time and we demonstrate that group sparsity-inducing penalties applied to GLM estimates of STRFs reduces the background noise while preserving the complex internal structure. The contribution of local spiking activity to the high-gamma power signal was factored out of the STRF using the GLM method, and this contribution was significant in 85 percent of the cases. Although the GLM methods have been used to estimate STRFs in animals, this study examines the detailed structure directly from auditory cortex in the awake human brain. We used this approach to identify an abrupt change in the best frequency of estimated STRFs along posteromedial-to-anterolateral recording locations along the long axis of Heschl’s gyrus. This change correlates well with a proposed transition from core to non-core auditory fields previously identified using the temporal response properties of Heschl’s gyrus recordings elicited by click-train stimuli.     

Auditory development between 7 and 11 years: an event-related potential (ERP) study

Background

There is considerable uncertainty about the time-course of central auditory maturation. On some indices, children appear to have adult-like competence by school age, whereas for other measures development follows a protracted course.

Methodology

We studied auditory development using auditory event-related potentials (ERPs) elicited by tones in 105 children on two occasions two years apart. Just over half of the children were 7 years initially and 9 years at follow-up, whereas the remainder were 9 years initially and 11 years at follow-up. We used conventional analysis of peaks in the auditory ERP, independent component analysis, and time-frequency analysis.

Principal Findings

We demonstrated maturational changes in the auditory ERP between 7 and 11 years, both using conventional peak measurements, and time-frequency analysis. The developmental trajectory was different for temporal vs. fronto-central electrode sites. Temporal electrode sites showed strong lateralisation of responses and no increase of low-frequency phase-resetting with age, whereas responses recorded from fronto-central electrode sites were not lateralised and showed progressive change with age. Fronto-central vs. temporal electrode sites also mapped onto independent components with differently oriented dipole sources in auditory cortex. A global measure of waveform shape proved to be the most effective method for distinguishing age bands.

Conclusions/Significance

The results supported the idea that different cortical regions mature at different rates. The ICC measure is proposed as the best measure of ‘auditory ERP age’.     

Effect of forward masking on evoked potentials of auditory cortex in guinea pigs

Thresholds of the event-related potentials (ERPs) appearance were measured for one stationary and four moving auditory images presented in silence or under forward masking conditions. The difference between thresholds in silence and after noise masker was considered as masking level. Under the forward masking, the amplitude of the ERP to the first click in the test series decreased in guinea pig auditory cortex. Masking level decreased with the time lag between signal and masker and didn't depend on the fused auditory image localization that corresponded to the first click in different test signals. This fact can support the hypothesis that for the long test signals the initial part can be masked more than the final one. The ERPs amplitude to next clicks in test series depended on interaction of two factors: forward masking in the "masker-signal" system and interaction of separate ERPs in the series evoked by the test signal.     

Differential effects of normal aging on sources of standard N1, target N1 and target P300 auditory event-related brain potentials revealed by low resolution electromagnetic tomography (LORETA)

The P300 event-related potential (ERP) is considered to be closely related to cognitive processes. In normal aging, P300 scalp latencies increase, parietal P300 scalp amplitudes decrease and the scalp potential field shifts to a relatively more frontal distribution. Based on ERPs recorded in 172 normal healthy subjects aged between 20 and 88 years in an auditory oddball paradigm, the effects of age on the electrical activity in the brain corresponding to N1 and P300 components were estimated by means of low resolution electromagnetic tomography (LORETA). This distributed approach directly computes a unique 3-dimensional electrical source distribution by assuming that neighbouring neurons are simultaneously and synchronously active. N1 LORETA generators, located predominantly in both auditory cortices and also symmetrically in prefrontal areas, increased with advancing age for standards but remained stable for targets. P300 LORETA generators, located symmetrically in the prefrontal cortex, in the parieto-occipital junction and in the inferior parietal cortex (supramarginal gyrus) and medially in the superior parietal cortex, were differentially affected by age. While age did not affect parieto-occipital sources, superior parietal and right prefrontal sources decreased pronouncedly. Thus, in normal aging, P300 current density decreased in regions were a fronto-parietal network for sustained attention was localized.     

Interstimulus interval and auditory event-related potentials in children: evidence for multiple generators

In the present study, the component structure of auditory event-related potentials (ERP) was studied in children of 7–9 years old by presenting stimuli with different interstimulus intervals (ISI). A short-term auditory sensory memory, as reflected by ISI effects on ERPs, was also studied. Auditory ERPs were recorded to brief unattended 1000 Hz frequent, `standard' and 1100 Hz rare, `deviant' (probability 0.1) tone stimuli with ISIs of 350, 700 and 1400 ms (in separate blocks). With the 350 ms-ISI, the ERP waveform to the standard stimulus consisted of P100-N250 peaks. With the two longer ISIs, in addition, the frontocentral N160 and N460 peaks were observed. Results suggested that N160, found with the longer ISIs, is a correlate of the adult auditory N1. In difference waves, obtained by subtracting ERP to standard stimuli from ERP to deviant stimuli, two negativities were revealed. The first was the mismatch negativity (MMN), which is elicited by any discriminable change in repetitive auditory input. The MMN data suggested that neural traces of auditory sensory memory lasted for at least 1400 ms, probably considerably longer, as no MMN attenuation was found across the ISIs used. The second, later negativity was similar to MMN in all aspects, except for the scalp distribution, which was posterior to that of the MMN.     

The Enhancement of the N1 Wave Elicited by Sensory Stimuli Presented at Very Short Inter-Stimulus Intervals Is a General Feature across Sensory Systems

Background

A paradoxical enhancement of the magnitude of the N1 wave of the auditory event-related potential (ERP) has been described when auditory stimuli are presented at very short (<400 ms) inter-stimulus intervals (ISI). Here, we examined whether this enhancement is specific for the auditory system, or whether it also affects ERPs elicited by stimuli belonging to other sensory modalities.

Methodology and Principal Findings

We recorded ERPs elicited by auditory and somatosensory stimuli in 13 healthy subjects. For each sensory modality, 4800 stimuli were presented. Auditory stimuli consisted in brief tones presented binaurally, and somatosensory stimuli consisted in constant-current electrical pulses applied to the right median nerve. Stimuli were delivered continuously, and the ISI was varied randomly between 100 and 1000 ms. We found that the ISI had a similar effect on both auditory and somatosensory ERPs. In both sensory modalities, ISI had an opposite effect on the magnitude of the N1 and P2 waves: the magnitude of the auditory and the somatosensory N1 was significantly increased at ISI≤200 ms, while the magnitude of the auditory and the somatosensory P2 was significantly decreased at ISI≤200 ms.

Conclusion and Significance

The observation that both the auditory and the somatosensory N1 are enhanced at short ISIs indicates that this phenomenon reflects a physiological property that is common across sensory systems, rather than, as previously suggested, unique for the auditory system. Two of the hypotheses most frequently put forward to explain this observation, namely (i) the decreased contribution of inhibitory postsynaptic potentials to the recorded scalp ERPs and (ii) the decreased contribution of ‘latent inhibition’, are discussed. Because neither of these two hypotheses can satisfactorily account for the concomitant reduction of the auditory and the somatosensory P2, we propose a third, novel hypothesis, consisting in the modulation of a single neural component contributing to both the N1 and the P2 waves.     

Differences between Spectro-Temporal Receptive Fields Derived from Artificial and Natural Stimuli in the Auditory Cortex

Spectro-temporal properties of auditory cortex neurons have been extensively studied with artificial sounds but it is still unclear whether they help in understanding neuronal responses to communication sounds. Here, we directly compared spectro-temporal receptive fields (STRFs) obtained from the same neurons using both artificial stimuli (dynamic moving ripples, DMRs) and natural stimuli (conspecific vocalizations) that were matched in terms of spectral content, average power and modulation spectrum. On a population of auditory cortex neurons exhibiting reliable tuning curves when tested with pure tones, significant STRFs were obtained for 62% of the cells with vocalizations and 68% with DMR. However, for many cells with significant vocalization-derived STRFs (STRF_voc) and DMR-derived STRFs (STRF_dmr), the BF, latency, bandwidth and global STRFs shape differed more than what would be predicted by spiking responses simulated by a linear model based on a non-homogenous Poisson process. Moreover STRF_voc predicted neural responses to vocalizations more accurately than STRF_dmr predicted neural response to DMRs, despite similar spike-timing reliability for both sets of stimuli. Cortical bursts, which potentially introduce nonlinearities in evoked responses, did not explain the differences between STRF_voc and STRF_dmr. Altogether, these results suggest that the nonlinearity of auditory cortical responses makes it difficult to predict responses to communication sounds from STRFs computed from artificial stimuli.     

A Simple ERP Method for Quantitative Analysis of Cognitive Workload in Myoelectric Prosthesis Control and Human-Machine Interaction

Common goals in the development of human-machine interface (HMI) technology are to reduce cognitive workload and increase function. However, objective and quantitative outcome measures assessing cognitive workload have not been standardized for HMI research. The present study examines the efficacy of a simple event-related potential (ERP) measure of cortical effort during myoelectric control of a virtual limb for use as an outcome tool. Participants trained and tested on two methods of control, direct control (DC) and pattern recognition control (PRC), while electroencephalographic (EEG) activity was recorded. Eighteen healthy participants with intact limbs were tested using DC and PRC under three conditions: passive viewing, easy, and hard. Novel auditory probes were presented at random intervals during testing, and significant task-difficulty effects were observed in the P200, P300, and a late positive potential (LPP), supporting the efficacy of ERPs as a cognitive workload measure in HMI tasks. LPP amplitude distinguished DC from PRC in the hard condition with higher amplitude in PRC, consistent with lower cognitive workload in PRC relative to DC for complex movements. Participants completed trials faster in the easy condition using DC relative to PRC, but completed trials more slowly using DC relative to PRC in the hard condition. The results provide promising support for ERPs as an outcome measure for cognitive workload in HMI research such as prosthetics, exoskeletons, and other assistive devices, and can be used to evaluate and guide new technologies for more intuitive HMI control.     

P300 and the menstrual cycle

Event-related potentials (ERPs) were elicited with an auditory discrimination paradigm in 20 adult female subjects on the first day of their menstrual cycles and approximately 14 days later. The amplitude and latency of the N1, P2, N2 and P3 (P300) components were measured for the two assessment times. No differences in either amplitude or latency for any of the components were observed as a function of menstrual cycle. Half the subjects who took oral contraceptives were compared to the other half who did not. No differences or interactions between these subgroups were obtained for any component amplitude or latency. It was concluded that menstrual cycle and use of oral contraceptives do not affect the P3 or other ERP components.     

Late divergence of target and nontarget ERPs in a visual oddball task

Different mental operations were expected in the late phase of intracerebral ERPs obtained in the visual oddball task with mental counting. Therefore we searched for late divergences of target and nontarget ERPs followed by components exceeding the temporal window of the P300 wave. Electrical activity from 152 brain regions of 14 epileptic patients was recorded by means of depth electrodes. Average target and nontarget records from 1800 ms long EEG periods free of epileptic activity were compared. Late divergence preceded by almost identical course of the target and nontarget ERPs was found in 16 brain regions of 6 patients. The mean latency of the divergence point was 570+/-93 ms after the stimulus onset. The target post-divergence section of the ERP differed from the nontarget one by opposite polarity, different latency of the components, or even different number of the components. Generators of post-divergence ERP components were found in the parahippocampal gyrus, superior, middle and inferior temporal gyri, amygdala, and fronto-orbital cortex. Finding of late divergence indicates that functional differences exist even not sooner than during the final phase of the task.     

Sensory-Motor Interactions for Vocal Pitch Monitoring in Non-Primary Human Auditory Cortex

The neural mechanisms underlying processing of auditory feedback during self-vocalization are poorly understood. One technique used to study the role of auditory feedback involves shifting the pitch of the feedback that a speaker receives, known as pitch-shifted feedback. We utilized a pitch shift self-vocalization and playback paradigm to investigate the underlying neural mechanisms of audio-vocal interaction. High-resolution electrocorticography (ECoG) signals were recorded directly from auditory cortex of 10 human subjects while they vocalized and received brief downward (−100 cents) pitch perturbations in their voice auditory feedback (speaking task). ECoG was also recorded when subjects passively listened to playback of their own pitch-shifted vocalizations. Feedback pitch perturbations elicited average evoked potential (AEP) and event-related band power (ERBP) responses, primarily in the high gamma (70–150 Hz) range, in focal areas of non-primary auditory cortex on superior temporal gyrus (STG). The AEPs and high gamma responses were both modulated by speaking compared with playback in a subset of STG contacts. From these contacts, a majority showed significant enhancement of high gamma power and AEP responses during speaking while the remaining contacts showed attenuated response amplitudes. The speaking-induced enhancement effect suggests that engaging the vocal motor system can modulate auditory cortical processing of self-produced sounds in such a way as to increase neural sensitivity for feedback pitch error detection. It is likely that mechanisms such as efference copies may be involved in this process, and modulation of AEP and high gamma responses imply that such modulatory effects may affect different cortical generators within distinctive functional networks that drive voice production and control.     

Perceptual organization of sound begins in the auditory periphery

Segmenting the complex acoustic mixture that makes a typical auditory scene into relevant perceptual objects is one of the main challenges of the auditory system [1], for both human and nonhuman species. Several recent studies indicate that perceptual auditory object formation, or "streaming," may be based on neural activity within the auditory cortex and beyond [2, 3]. Here, we find that scene analysis starts much earlier in the auditory pathways. Single units were recorded from a peripheral structure of the mammalian auditory brainstem, the cochlear nucleus. Peripheral responses were similar to cortical responses and displayed all of the functional properties required for streaming, including multisecond adaptation. Behavioral streaming was also measured in human listeners. Neurometric functions derived from the peripheral responses predicted accurately behavioral streaming. This reveals that subcortical structures may already contribute to the analysis of auditory scenes. This finding is consistent with the observation that species lacking a neocortex can still achieve and benefit from behavioral streaming [4]. For humans, we argue that auditory scene analysis of complex scenes is probably based on interactions between subcortical and cortical neural processes, with the relative contribution of each stage depending on the nature of the acoustic cues forming the streams.