Generation Of Event-related Potentials Research Articles

Processing of emotional connotations in Chinese monomorphic and compound words reflected by the early posterior negativity.

Writing stands as one of humanity's most profound inventions, facilitating the efficient sharing and transmission of vast amounts of information. Similar to images and facial expressions, visual (written) words possess the ability to evoke emotional connotations. Understanding how the brain perceives these emotional nuances encoded in highly symbolic visual words is a key focus of the emerging field of "affective neurolinguistics." At the core of this inquiry lies the examination of the early posterior negativity (EPN), an event-related potentials (ERPs) component peaking around 300 ms after stimulus onset in the occipitotemporal scalp region. EPN has consistently emerged in response to emotional stimuli, encompassing pictures, faces, and visual words. However, prior research has notably lacked observation of EPN in response to Chinese emotional words, raising questions about potential differences in emotional processing between Chinese and other languages. Given the logographic nature of the Chinese writing system and the prevalence of compound words in the Chinese lexicon, this study aims to explore whether the emotional processing of Chinese monomorphic and compound words elicits an EPN response. Two experiments were conducted: Experiment 1 utilized one-character words (monomorphic words), while Experiment 2 employed two-character words (compound words). Participants were assigned a go/no-go task, instructed to respond to unknown words (word recognition task) or blue stimuli (color decision task). Data analysis using a data-driven mass univariate approach revealed significant ERP differences between emotional and neutral words. Notably, the time course, scalp topography, and cortical generators of the difference ERP presented a characteristic EPN response in both experiments. These findings strongly support the notion that the processing of emotional connotations in both Chinese monomorphic and compound words is reflected by the EPN, paving the way for future research using EPN as an emotion-related ERP component for investigating emotional processing of Chinese words.

Neural correlates of face perception modeled with a convolutional recurrent neural network

Objective. Event-related potential (ERP) sensitivity to faces is predominantly characterized by an N170 peak that has greater amplitude and shorter latency when elicited by human faces than images of other objects. We aimed to develop a computational model of visual ERP generation to study this phenomenon which consisted of a three-dimensional convolutional neural network (CNN) connected to a recurrent neural network (RNN). Approach. The CNN provided image representation learning, complimenting sequence learning of the RNN for modeling visually-evoked potentials. We used open-access data from ERP Compendium of Open Resources and Experiments (40 subjects) to develop the model, generated synthetic images for simulating experiments with a generative adversarial network, then collected additional data (16 subjects) to validate predictions of these simulations. For modeling, visual stimuli presented during ERP experiments were represented as sequences of images (time x pixels). These were provided as inputs to the model. By filtering and pooling over spatial dimensions, the CNN transformed these inputs into sequences of vectors that were passed to the RNN. The ERP waveforms evoked by visual stimuli were provided to the RNN as labels for supervised learning. The whole model was trained end-to-end using data from the open-access dataset to reproduce ERP waveforms evoked by visual events. Main results. Cross-validation model outputs strongly correlated with open-access (r = 0.98) and validation study data (r = 0.78). Open-access and validation study data correlated similarly (r = 0.81). Some aspects of model behavior were consistent with neural recordings while others were not, suggesting promising albeit limited capacity for modeling the neurophysiology of face-sensitive ERP generation. Significance. The approach developed in this work is potentially of significant value for visual neuroscience research, where it may be adapted for multiple contexts to study computational relationships between visual stimuli and evoked neural activity.

A Guided Tutorial on Modelling Human Event-Related Potentials with Recurrent Neural Networks

In cognitive neuroscience research, computational models of event-related potentials (ERP) can provide a means of developing explanatory hypotheses for the observed waveforms. However, researchers trained in cognitive neurosciences may face technical challenges in implementing these models. This paper provides a tutorial on developing recurrent neural network (RNN) models of ERP waveforms in order to facilitate broader use of computational models in ERP research. To exemplify the RNN model usage, the P3 component evoked by target and non-target visual events, measured at channel Pz, is examined. Input representations of experimental events and corresponding ERP labels are used to optimize the RNN in a supervised learning paradigm. Linking one input representation with multiple ERP waveform labels, then optimizing the RNN to minimize mean-squared-error loss, causes the RNN output to approximate the grand-average ERP waveform. Behavior of the RNN can then be evaluated as a model of the computational principles underlying ERP generation. Aside from fitting such a model, the current tutorial will also demonstrate how to classify hidden units of the RNN by their temporal responses and characterize them using principal component analysis. Statistical hypothesis testing can also be applied to these data. This paper focuses on presenting the modelling approach and subsequent analysis of model outputs in a how-to format, using publicly available data and shared code. While relatively less emphasis is placed on specific interpretations of P3 response generation, the results initiate some interesting discussion points.

Phase Analysis of Event-Related Potentials Based on Dynamic Mode Decomposition

Real-time detection of event-related potentials (ERPs) and exploration of ERPs generation mechanisms are vital to practical application of brain–computer interfaces (BCI). Traditional methods for ERPs analysis often fall into time domain, time–frequency domain, or spatial domain. Methods which can reveal spatiotemporal interactions by simultaneously analyzing multi-channel EEG signals may provide new insights into ERP research and is highly desired. Additionally, although phase information has been investigated to describe the phase consistency of a certain frequency component across different ERP trials, it is of research significance to analyze the phase reorganization across different frequency components that constitute a single-trial ERP signal. To address these problems, dynamic mode decomposition (DMD) was applied to decompose multi-channel EEG into a series of spatial–temporal coherent DMD modes, and a new metric, called phase variance distribution (PVD) is proposed as an index of the phase reorganization of DMD modes during the ERP in a single trial. Based on the PVD, a new error-related potential (ErrP) detection method based on symmetric positive defined in Riemann manifold is proposed to demonstrate the significant PVD differences between correct and error trials. By including the phase reorganization index, the 10-fold cross-validation results of an ErrP detection task showed that the proposed method is 4.98%, 27.99% and 7.98% higher than the counterpart waveform-based ErrP detection method in the terms of weighted accuracy rate, precision and recall of the ErrP class, respectively. The resulting PVD curve shows that with the occurrence of ERP peaks, the phases of different frequency rhythms are getting to aligned and yields a significant smaller PVD. Since the DMD modes of different frequencies characterize spatiotemporal coherence of multi-channel EEG at different functional regions, the new phase reorganization index, PVD, may indicate the instantaneous phase alignment of different functional networks and sheds light on a new interpretation of ERP generation mechanism.

Neural generators involved in visual cue processing in children with attention-deficit/hyperactivity disorder (ADHD).

Event-related potentials (ERP) studies report alterations in the ongoing visuo-attentional processes in children with attention-deficit/hyperactivity disorder (ADHD). We hypothesized that the neural generators progressively recruited after a cue stimulus imply executive-related areas well before engagement in executive processing in children with ADHD compared to typically developed children (TDC). We computed source localization (swLORETA) of the ERP and ERSP evoked by the Cue stimulus during a visual Cue-Go/Nogo paradigm in 15 ADHD compared to 16 TDC. A significant difference in N200/P200 amplitude over the right centro-frontal regions was observed between ADHD and TDC, supported by a stronger contribution of the left visuo-motor coordination area, premotor cortex, and prefrontal cortex in ADHD. In addition, we recorded a greater beta power spectrum in ADHD during the 80-230ms interval, which was explained by increased activity in occipito-parieto-central areas and lower activity in the left supramarginal gyrus and prefrontal areas in ADHD. Successive analysis of the ERP generators (0-500ms with successive periods of 50ms) revealed significant differences beginning at 50ms, with higher activity in the ventral anterior cingulate cortex, premotor cortex, and fusiform gyrus, and ending at 400-500ms with higher activity of the dorsolateral prefrontal cortex and lower activity of the posterior cingulate cortex in ADHD compared to TDC. The areas contributing to ERP in ADHD and TDC differ from the early steps of visuo-attentional processing and reveal an overinvestment of the executive networks interfering with the activity of the dorsal attention network in children with ADHD.

\u201cHit the missing stimulus\u201d. A simultaneous EEG-fMRI study to localize the generators of endogenous ERPs in an omitted target paradigm

Event-Related Potentials (ERPs) occurring independently from any stimulus are purely endogenous (emitted potentials) and their neural generators can be unequivocally linked with cognitive processes. In the present study, the subjects performed two similar visual counting tasks: a standard two-stimulus oddball, and an omitted-target oddball task, characterized by the physical absence of the target stimulus. Our investigation aimed at localizing the neural sources of the scalp-recorded endogenous/emitted ERPs. To optimize the source localization, the high temporal resolution of electrophysiology was combined with the fine spatial information provided by the simultaneous recording of functional magnetic resonance (fMRI). Both tasks identified two endogenous ERP components in the 300 to 520 ms interval. An earlier component, pP2, showed a bilateral generator in the anterior Insula. A later P3 component (P3b) was generated bilaterally in the temporal-parietal junction, the premotor and motor area and the anterior intraparietal sulcus (this latter one only in the standard oddball). Anticipatory slow waves (beginning 900 to 500 ms pre-stimulus), also of endogenous nature, were produced by the inferior and middle frontal gyrus and the supplementary and cingulate motor areas. Our protocol disentangled pre- from post-stimulus fMRI activations and provided original clues to the psychophysiological interpretation of emitted/endogenous ERPs.

HYBRID BRAIN–COMPUTER INTERFACE PARADIGM — A STUDY

The advancements in the field of brain–computer interface (BCI) are driven by the underlying motive of improving quality of life for both healthy as well as locked in subjects. Since BCI’s are based on the response of the human brain to training or external stimuli, the improvement in terms of performance can be achieved by either enhancing the subject training procedure or by improving the external stimuli to produce maximized event related potential (ERP). P300 and steady-state visually evoked potential (SSVEP) approaches have been the most common paradigms used for stimulus-based BCI’s world over. But recently, a large number of researchers are facing a problem of BCI illiteracy in subjects, where some of the subjects showed ineffective results while training with these BCI as independent stimuli. The concept of hybrid brain–computer interface (hBCI) is a step towards eradicating this problem. Our research deals with external stimuli-based ERP generation where we discuss and compare with experimentation, three different options of visual stimulus: conventional SSVEP stimulus, P300-SSVEP hybrid stimulus, distinct target colors for P300-SSVEP-based hybrid stimulus. This paper introduces a novel hBCI paradigm and discusses the validation of improved results by comparing with the already existing stimuli options. The parameters of comparison that were considered to validate our proposal were decision accuracy (Acc), information transfer rate (ITR) and false activation rate (FAR).

P 141 Cerebellar impacts on neural networks of emotional attention as evidenced by event related potentials

Background The cerebellum is highly indicative to contributions to high-order functions of emotion, supporting responsible domains of cerebral neural networks in processing of distinct emotional cues. So the impact of the attentional modes of the cerebellum deems of particular interest for separating a selective pathway of emotionally driven cues, corresponding neurophysiological patterns in cerebellar disorders might provide further informations about the cerebellar role in emotional attention. Methods Eight patients with a ischemic lesion of the cerebellum (five unilateral, three bilateral) and seven patients without stroke history were studied. Four neurophysiological paradigms were engaged along a confined set of the International Affective Picture System (IAPS) with neutral as well as emotional cues of different valence and arousal, each presented in a protocolled stream. Event-related Potentials (ERP) of early and late processing stages of selective and divided attention to stimulus processing were recorded by a 129 sensor array (Geodesic Inc.). Results In opposite to control subjects, patients with a cerebellar lesion predominately of the posterior lobe showed a deviant early posterior negativity (EPN) at temporo-occipital locations in paradigms probing the divided attention to emotional arousing cues, whereby these effects were only significant for the acccording cognitive ERP (P200, P300). Patients with a cerebellar lesion in opposite to control subjects showed also a reduction of the Late Positive Potentials (LPP) at centro-parietal locations, whereby this observation was without a striking statistical significance rather due to the small sample size. Conclusions Patients of cerebellar damage in our study disclosed neurophysiological patterns of impaired divided attention at the early stage and presumably also at forwarding stages of emotional processing. According to the findings of preserved selective attention to emotional cues as well as the indicative neurophysiologic patterns of enhanced cognitive activities mainly served by domains of the attentional and executive functions, compensatory guidance of the ventromedial and dorsolateral prefrontal cortex are highly warranted as crucial to ERP generation in our study sample. In respect to some restrictions of statistical output, application of the used paradigms to a greater study sample as well as a more in-depth analysis of the dipole sources should provide an increased precision of concerned regions of neural ERP generation.

Objective assessment of perceived effort in listening by employing EEG feature.

The adjustment of hearing aid devices can heavily depend on the subjective feedback of the patients. Our aim is to investigate measures that can be used objectively to state a subject's listening effort. To obtain a comprehensive and reliable measure as an indicator for a person's listening effort, we need to have a better understanding of electroencephalograpic (EEG) activities. Decoding EEG signals specifically by the analysis of the instantaneous phase information has been a new trend in the last decades. Throughout many studies conducted in the past, it has been shown that the instantaneous phase of oscillatory signals reset in relation to various cognitive processes. This is based on a hypothesis presented for the generation of event related potentials. In this study, we measure the degree of phase re-organization through fitting a von Mises distribution to EEG recordings. The concentration parameter of a von Mises distribution has been shown as an informative feature for reflecting the level of attention. This feature has been used for predicting the listening effort and the results are compared among three different hearing aid settings.

Use of a steady-state baseline to address evoked vs. oscillation models of visual evoked potential origin

There has been a long debate about the neural mechanism of event-related potentials (ERPs). Previously, no evidence or method was apparent to validate the two competing models, the evoked model and the oscillation model. One argument is whether the pre-stimulus brain oscillation could influence the following ERP. This study carried out an innovative visual oddball task experiment to investigate the dynamic process of visual evoked potentials. A period of stable oscillations of specified dominant frequencies and initial phases, i.e. the steady-state baseline, would be induced before responses to transient stimuli of different contrasts, which could overcome the artifact problem caused by the ‘sorting’ method. The result first revealed a ‘three-period-transition’ for the generation of visual evoked potentials by an objective decomposition. The ERP almost retained the preceding oscillation during the first period, provided an unstable negative potential in the second period, and generated the N1 component in the third period. The cross term analysis showed that the evoked model couldn't be the whole explanation for the ERP generation. Furthermore, the component analysis revealed that the N1 latency was sensitive to the initial phase under the low stimulus contrast (supporting the oscillation model) but not under the high stimulus contrast (supporting the evoked model). It demonstrated that the external stimulus contrast is a significant factor deciding the explicit model for ERPs. Our method and preliminary results may help reconcile the previous, seemly contradictory findings on the ERP mechanism.

A frontal cortex event-related potential driven by the basal forebrain.

Event-related potentials (ERPs) are widely used in both healthy and neuropsychiatric conditions as physiological indices of cognitive functions. Contrary to the common belief that cognitive ERPs are generated by local activity within the cerebral cortex, here we show that an attention-related ERP in the frontal cortex is correlated with, and likely generated by, subcortical inputs from the basal forebrain (BF). In rats performing an auditory oddball task, both the amplitude and timing of the frontal ERP were coupled with BF neuronal activity in single trials. The local field potentials (LFPs) associated with the frontal ERP, concentrated in deep cortical layers corresponding to the zone of BF input, were similarly coupled with BF activity and consistently triggered by BF electrical stimulation within 5-10 msec. These results highlight the important and previously unrecognized role of long-range subcortical inputs from the BF in the generation of cognitive ERPs. DOI: http://dx.doi.org/10.7554/eLife.02148.001.

Analysis of EEG phase properties with pulse and noise stimuli in visual cortex (V1)

AbstractThe event‐related potential (ERP) of brain EEG (electroencephalogram) activity plays an important role in EEG phase synchronization and/or hemodynamic responses measured by fMRI (functional magnetic resonance imaging). However, the specific mechanism of ERP generation is still unclear. In this study, pulse and noise‐type visual stimuli were administered to subjects. Then the phase response of the EEG in α‐waves was analyzed. The magnitudes of the phase response were found to vary with the stimulus administered phase and no power increase was observed. These results indicate that the ERP in α‐waves is generated by phase resetting of brain activity. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(7): 58–64, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11368

Single-trial coupling of EEG and fMRI during recognition reveals the generators of ERP old/new effects

Event Abstract Back to Event Single-trial coupling of EEG and fMRI during recognition reveals the generators of ERP old/new effects Michael Hoppstädter1, 2*, Christian Bäuchl1, 2, Carsten Diener1, 2, Herta Flor1, 2 and Patric Meyer1, 2 1 Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Department of Cognitive and Clinical Neuroscience, Germany 2 Bernstein Center for Computational Neuroscience Heidelberg/Mannheim, Germany Recognition means the ability to decide if information was encountered previously. This can be featured with additional details from the encoding episode or not. Various behavioural, electrophysiological and imaging studies have pinpointed that two differential processes are involved in recognition memory, namely recollection and familiarity. Recollection describes the conscious retrieval of contextual information about a specific episode, while familiarity means only a feeling of knowing without additional contextual details. These processes may be differentiated electrophysiologically by means of event-related potentials (ERPs). In contrast to correctly rejected new items, items correctly classified as old yield a more positive ERP deflection which is termed old/new effect. One earlier frontally localized old/new effect emerging from about 300 ms after stimulus onset relates to familiarity processing whereas a functionally distinct later parietal effect is associated with recollection. Functional magnetic resonance imaging (fMRI) has revealed that within the medial temporal lobe, extrahippocampal cortical areas and the hippocampus proper support independently recognition based on familiarity or recollection, respectively. In order to examine the relation between hemodynamic changes and the modulation of ERP old/new effects during memory retrieval, we conducted a simultaneous EEG-fMRI study in 16 young healthy volunteers. Standard ERP analyses revealed an early mid-frontal and a later parietal old/new effect, presumably associated to the differential use of familiarity and recollection during recognition. FMRI old/new contrasts showed activity modulation in the hippocampus as well as in the precuneus, the retrosplenial cortex and the medial frontal gyrus. An EEG-informed fMRI analysis was performed to relate single-trial ERP amplitudes to hemodynamic signal changes, thus accounting for trial-to-trial fluctuations. By orthogonalisation to the standard stimulus-coding predictors the variance explained by the trial-to-trial modulation of the old/new effects was isolated. The results complement rare data from intracranial ERP recordings and patient studies. The results from this multimodal fusion analysis will be embedded into biophysically and anatomically detailed models of hippocampal-prefrontal interaction which will in turn generate predictors for the outcome of future imaging studies. Acknowledgements This study was supported by the Bundesministerium für Bildung und Forschung. Keywords: EEG-fMRI, Long-term memory, medial temporal lobe, retrieval Conference: Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012. Presentation Type: Poster Topic: Learning, plasticity, memory Citation: Hoppstädter M, Bäuchl C, Diener C, Flor H and Meyer P (2012). Single-trial coupling of EEG and fMRI during recognition reveals the generators of ERP old/new effects. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference 2012. doi: 10.3389/conf.fncom.2012.55.00122 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 11 May 2012; Published Online: 12 Sep 2012. * Correspondence: Mr. Michael Hoppstädter, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Department of Cognitive and Clinical Neuroscience, Mannheim, Germany, michael.hoppstaedter@zi-mannheim.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Michael Hoppstädter Christian Bäuchl Carsten Diener Herta Flor Patric Meyer Google Michael Hoppstädter Christian Bäuchl Carsten Diener Herta Flor Patric Meyer Google Scholar Michael Hoppstädter Christian Bäuchl Carsten Diener Herta Flor Patric Meyer PubMed Michael Hoppstädter Christian Bäuchl Carsten Diener Herta Flor Patric Meyer Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Time course of ERP generators to syllables in infants: A source localization study using age-appropriate brain templates

Event-related potentials (ERPs) have become an important tool in the quest to understand how infants process perceptual information. Identification of the activation loci of the ERP generators is a technique that provides an opportunity to explore the neural substrates that underlie auditory processing. Nevertheless, as infant brain templates from healthy, non-clinical samples have not been available, the majority of source localization studies in infants have used non-realistic head models, or brain templates derived from older children or adults. Given the dramatic structural changes seen across infancy, all of which profoundly affect the electrical fields measured with EEG, it is important to use individual MRIs or age-appropriate brain templates and parameters to explore the localization and time course of auditory ERP sources. In this study 6-month-old infants were presented with a passive oddball paradigm using consonant-vowel (CV) syllables that differed in voice onset time. Dense-array EEG/ERPs were collected while the infants were awake and alert. In addition, MRIs were acquired during natural non-sedated sleep for a subset of the sample. Discrete dipole and distributed source models were mapped onto individual and averaged infant MRIs. The CV syllables elicited a positive deflection at about 200 ms followed by a negative deflection that peaked around 400 ms. The source models generated placed the dipoles at temporal areas close to auditory cortex for both positive and negative responses. Notably, an additional dipole for the positive peak was localized at the frontal area, at the anterior cingulate cortex (ACC) level. ACC activation has been reported in adults, but has not, to date, been reported in infants during processing of speech-related signals. The frontal ACC activation was earlier but smaller in amplitude than the left and right auditory temporal activations. These results demonstrate that in infancy the ERP generators to CV syllables are localized in cortical areas similar to that reported in adults, but exhibit a notably different temporal course. Specifically, ACC activation in infants significantly precedes auditory temporal activation, whereas in adults ACC activation follows that of temporal cortex. We suggest that these timing differences could be related to current maturational changes, to the ongoing construction of language-specific phonetic maps, and/or to more sensitive attentional switching as a response to speech signals in infancy.

Early Sensory Contributions to Contextual Encoding Deficits in Schizophrenia

The AX version of the visual continuous performance task (AX-CPT) is widely used for investigating visual working memory dysfunction in schizophrenia. Event-related potentials (ERP) provide an objective index of brain function and can be used to evaluate brain substrates underlying impaired cognition in schizophrenia. To assess the mechanisms that underlie visual working memory dysfunction in schizophrenia relative to impairment of early visual processing. Case-control study. Inpatient and outpatient facilities associated with the Nathan Kline Institute for Psychiatric Research. A total of 30 individuals with schizophrenia and 17 healthy comparison subjects. Three versions of the AX-CPT, with parametric variations in the proportions of trial types, were used to test performance and underlying neural activity during differential challenge situations. Contrast sensitivity measures were obtained from most subjects. Behavioral performance was assessed using d' context scores. Integrity of stimulus- and task-related cortical activation to both cue and probe stimuli was assessed using sensory (C1, P1, N1) and cognitive (N2, contingent negative variation [CNV]) ERP components. Early magnocellular/parvocellular function was assessed using contrast sensitivity. Linear regression and path analyses were used to assess relations between physiological and behavioral parameters. Patients showed reduced amplitude of both early sensory (P1, N1) and later cognitive (N2, CNV) ERP components. Deficits in sensory (N1) and cognitive (N2) component activation to cue stimuli contributed independently to impaired behavioral performance. In addition, sensory deficits predicted impaired cognitive ERP generation. Finally, deficits in performance correlated with impairments in contrast sensitivity to low, but not high, spatial frequency stimuli. Working memory deficits in schizophrenia have increasingly been attributed to impairments in stimulus encoding rather than to failures in memory retention. This study provides objective physiological support for encoding hypotheses. Further, deficits in sensory processing contribute significantly to impaired working memory performance, consistent with generalized neurochemical models of schizophrenia.

Distinct neural responses to chord violations: A multiple source analysis study

The human brain is constantly predicting the auditory environment by representing sequential similarities and extracting temporal regularities. It has been proposed that simple auditory regularities are extracted at lower stations of the auditory cortex and more complex ones at other brain regions, such as the prefrontal cortex. Deviations from auditory regularities elicit a family of early negative electric potentials distributed over the frontal regions of the scalp. In this study, we wished to disentangle the brain processes associated with sequential vs. hierarchical auditory regularities in a musical context by studying the event-related potentials (ERPs), the behavioral responses to violations of these regularities, and the localization of the underlying ERP generators using two different source analysis algorithms. To this aim, participants listened to musical cadences constituted by seven chords, each containing either harmonically congruous chords, harmonically incongruous chords, or harmonically congruous but mistuned chords. EEG was recorded and multiple source analysis was performed. Incongruous chords violating the rules of harmony elicited a bilateral ERAN, whereas mistuned chords within chord sequences elicited a right-lateralized MMN. We found that the dominant cortical sources for the ERAN were localized around Broca's area and its right homolog, whereas the MMN generators were localized around the primary auditory cortex. These findings suggest a predominant role of the auditory cortices in detecting sequential scale regularities and the posterior prefrontal cortex in parsing hierarchical regularities in music.

Analysis of EEG Phase Property with Pulse and Noise Stimuli in Visual Cortex (V1)

Event Related Potential (ERP) of brain EEG (Electroencephalogram) activity plays an important role in EEG phase synchronization and/or hemodynamic responses measured by fMRI (functional Magnetic Resonance Imaging). However, the specific mechanism of ERP generation is still unclear. In this study, pulse and noise type visual stimuli are administered to subjects. Then the phase response of the EEG in α-waves is analyzed. As a result, the magnitudes of the phase response are varied by the stimulus administered phase and no power increase is observed. These results indicate that the ERP in α-waves is generated by the phase resetting of brain activity.

Source localization of event-related potentials to pitch change mapped onto age-appropriate MRIs at 6 months of age

Auditory event-related potentials (ERPs) have been used to understand how the brain processes auditory input, and to track developmental change in sensory systems. Localizing ERP generators can provide invaluable insights into how and where auditory information is processed. However, age-appropriate infant brain templates have not been available to aid such developmental mapping. In this study, auditory change detection responses of brain ERPs were examined in 6-month-old infants using discrete and distributed source localization methods mapped onto age-appropriate magnetic resonance images. Infants received a passive oddball paradigm using fast-rate non-linguistic auditory stimuli (tone doublets) with the deviant incorporating a pitch change for the second tone. Data was processed using two different high-pass filters. When a 0.5Hz filter was used, the response to the pitch change was a large frontocentral positive component. When a 3Hz filter was applied, two temporally consecutive components associated with change detection were seen: one with negative voltage, and another with positive voltage over frontocentral areas. Both components were localized close to the auditory cortex with an additional source near to the anterior cingulate cortex. The sources for the negative response had a more tangential orientation relative to the supratemporal plane compared to the positive response, which showed a more lateral, oblique orientation. The results described here suggest that at 6months of age infants generate similar response patterns and use analogous cortical areas to that of adults to detect changes in the auditory environment. Moreover, the source locations and orientations, together with waveform topography and morphology provide evidence in infants for feature-specific change detection followed by involuntary switching of attention.

Cognitive activities in the subthalamic nucleus. Invasive studies

According to our studies, based on intracerebral recordings of cognitive Event Related Potentials (ERP), the cognitive activities in the the Basal Ganglia (BG) are organized in some way other than the well-known organization of the cortico-BG-thalamocortical circuits. The cognitive role of the subthalamic nucleus (STN) has been largely unknown. Direct connections with the cortex that bypass the circuitries might underlie the processing of specific cognitive functions in the STN. STN seems to be specifically involved in the processing of some cognitive activities, e.g. of the executive functions. A modified protocol with a dual task elicited local field ERP within the STN. Impact of cortical 1 Hz rTMS on STN was tested. ERD/S in was tested in visuomotor tasks with single letters writing. No generators of ERP (P3-like potentials) were elicited by the standard oddball protocol in the STN (at variance with recordings from the putamen, caudate and pallidum). rTMS over the right inferior frontal cortex caused a shortening of latencies of ERP in standard and dual protocols. No changes were observable after the rTMS over the dorzolateral prefrontal cortex and sham stimulation. In the STN, only the tasks with an increased demand on executive functions produced the alpha and beta ERD/S (event-related desynchronization/synchronization). Our results indicate a specific, task-related involvement of the STN in the cognitive activities. Cognitive processing in the STN is possibly processed via hyperdirect cortico-STN pathway. Certain effects of DBS surgery on cognitive performance could be explained by a direct effect on 'cognitive' parts of the STN.

What do ERPs and ERFs Reveal About the Effect of Antipsychotic Treatment on Cognition in Schizophrenia?

Cognitive dysfunction is considered to be a core feature in schizophrenia. It is believed that antipsychotic drugs, especially atypical ones, could improve cognitive functions in schizophrenia patients. Auditory event-related potentials (ERPs) such as mismatch negativity (MMN) and P300 response are potential candidates for objective investigation of pre-attentional and attention-dependent processing in schizophrenia patients, respectively. Both these responses were found to be altered in schizophrenia. Moreover, neurotransmitters play important role in generation of MMN and P300 components. Therefore, these ERPs are potential candidates for monitoring the cognitive changes caused by neurochemical modulation during antipsychotic treatment in schizophrenia patients. In addition, neurochemical ERP generation mechanisms discovered during drug-challenge studies in healthy subjects could explain these ERP findings in patients. To date, no effect of antipsychotic treatment on MMN was observed, whereas certain antipsychotics (e.g. clozapine) could modulate P300 response. At the same time, adjunctive glutamate-system affecting therapy seems to influence MMN response. The explanation of these phenomena could be a weak relationship between dopaminergic activities and MMN response and a strong connection between glutamate NMDA receptors and MMN generation. As to the P300 component, because of the multiple generators, it is more sensitive to the influences of different neurochemical activities. In the future, the combination of transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) with electroencephalography (EEG) will open new possibilities for understanding the drug-induced changes on the neural substrates of information processing in schizophrenia patients.