Brain source localization of MMN, P300 and N400: Aging and gender differences

Large-scale analysis of neural activity and connectivity from high-density electroencephalographic data

INTRODUCTION

High-density electroencephalography (hdEEG) is a technique used for the characterization of the neural activity and connectivity in the human brain. The analysis of EEG data involves several steps, including signal pre-processing, head modelling, source localization and activity/connectivity quantification. Visual check of the analysis steps is often necessary, making the process time- and resource-consuming and, therefore, not feasible for large datasets.

FINDINGS

Here we present the Noninvasive Electrophysiology Toolbox (NET), an open-source software for large-scale analysis of hdEEG data, running on the cross-platform MATLAB environment. NET combines all the tools required for a complete hdEEG analysis workflow, from raw signals to final measured values. By relying on reconstructed neural signals in the brain, NET can perform traditional analyses of time-locked neural responses, as well as more advanced functional connectivity and brain mapping analyses. The extracted quantitative neural data can be exported to provide broad compatibility with other software.

CONCLUSIONS

NET is freely available (https://github.com/bind-group-kul/net) under the GNU public license for non-commercial use and open-source development, together with a graphical user interface (GUI) and a user tutorial. While NET can be used interactively with the GUI, it is primarily aimed at unsupervised automation to process large hdEEG datasets efficiently. Its implementation creates indeed a highly customizable program suitable for analysis automation and tight integration into existing workflows.

The accuracy of different mismatch negativity amplitude representations in predicting the levels of consciousness in patients with disorders of consciousness

Introduction

The mismatch negativity (MMN) index has been used to evaluate consciousness levels in patients with disorders of consciousness (DoC). Indeed, MMN has been validated for the diagnosis of vegetative state/unresponsive wakefulness syndrome (VS/UWS) and minimally conscious state (MCS). In this study, we evaluated the accuracy of different MMN amplitude representations in predicting levels of consciousness.

Methods

Task-state electroencephalography (EEG) data were obtained from 67 patients with DoC (35 VS and 32 MCS). We performed a microstate analysis of the task-state EEG and used four different representations (the peak amplitude of MMN at electrode Fz (Peak), the average amplitude within a time window -25- 25 ms entered on the latency of peak MMN component (Avg for peak ± 25 ms), the average amplitude of averaged difference wave for 100-250 ms (Avg for 100-250 ms), and the average amplitude difference between the standard stimulus ("S") and the deviant stimulus ("D") at the time corresponding to Microstate 1 (MS1) (Avg for MS1) of the MMN amplitude to predict the levels of consciousness.

Results

The results showed that among the four microstates clustered, MS1 showed statistical significance in terms of time proportion during the 100-250 ms period. Our results confirmed the activation patterns of MMN through functional connectivity analysis. Among the four MMN amplitude representations, the microstate-based representation showed the highest accuracy in distinguishing different levels of consciousness in patients with DoC (AUC = 0.89).

Conclusion

We discovered a prediction model based on microstate calculation of MMN amplitude can accurately distinguish between MCS and VS states. And the functional connection of the MS1 is consistent with the activation mode of MMN.

Reduced magnetic mismatch negativity: a shared deficit in psychosis and related risk

BACKGROUND

Abnormal auditory processing of deviant stimuli, as reflected by mismatch negativity (MMN), is often reported in schizophrenia (SCZ). At present, it is still under debate whether this dysfunctional response is specific to the full-blown SCZ diagnosis or rather a marker of psychosis in general. The present study tested MMN in patients with SCZ, bipolar disorder (BD), first episode of psychosis (FEP), and in people at clinical high risk for psychosis (CHR).

METHODS

Source-based MEG activity evoked during a passive auditory oddball task was recorded from 135 patients grouped according to diagnosis (SCZ, BD, FEP, and CHR) and 135 healthy controls also divided into four subgroups, age- and gender-matched with diagnostic subgroups. The magnetic MMN (mMMN) was analyzed as event-related field (ERF), Theta power, and Theta inter-trial phase coherence (ITPC).

RESULTS

The clinical group as a whole showed reduced mMMN ERF amplitude, Theta power, and Theta ITPC, without any statistically significant interaction between diagnosis and mMMN reductions. The mMMN subgroup contrasts showed lower ERF amplitude in all the diagnostic subgroups. In the analysis of Theta frequency, SCZ showed significant power and ITPC reductions, while only indications of diminished ITPC were observed in CHR, but no significant decreases characterized BD and FEP.

CONCLUSIONS

Significant mMMN alterations in people experiencing psychosis, also for diagnoses other than SCZ, suggest that this neurophysiological response may be a feature shared across psychotic disorders. Additionally, reduced Theta ITPC may be associated with risk for psychosis.

Auditory P300 in individuals with high schizotypy: associations of schizotypal traits with amplitude and latency under different oddball conditions

Background

The aim of this study was to compare the characteristics of auditory P300 between non-clinical individuals with high and low schizotypal traits, and investigate the relationship between schizotypy and P300 under various oddball conditions.

Methods

An extreme-group design was adopted. After screening 1,519 young adults using the Schizotypal Personality Questionnaire (SPQ), sixty-three participants were chosen and divided into two groups (schizotypy group: 31 participants; control group: 32 participants). Basic demographic information was assessed and matched between groups. Depression and anxiety indexes were evaluated and controlled. The P300 component was evoked by an auditory oddball paradigm with different frequencies and durations.

Results

(1) The duration P300 amplitude at PZ site was significantly weaker in the schizotypy group than in the control group [F(1,54) = 7.455, p = 0.009, η_p² = 0.121]. (2) In the schizotypy group, the latency of frequency P300 at PZ site under large-variant oddball condition was significantly correlated with total SPQ scores (r_p = 0.451, p = 0.018) and disorganized dimension scores (r_p = 0.381, p = 0.050). (3) In the control group, significantly negative correlations was found between the negative dimension score of SPQ and the frequency P300 amplitudes under small variant condition (PZ: r_p = -0.393, p = 0.043; CPZ: r_p = -0.406, p = 0.035). In addition, a significant negative relationship was found between disorganized dimension scores and the duration P300 latency at CPZ site under large-variant oddball condition (r_p = -0.518, p = 0.006). Moreover, a significant negative association was found between the duration P300 amplitude at CPZ site under small-variant oddball condition and negative factor scores (r_p = -0.410, p = 0.034).

Conclusion

Individuals with high schizotypal traits were likely to have deficient attention and hypoactive working memory for processing auditory information, especially the duration of sounds. P300 effects were correlated with negative and disorganized schizotypy, rather than positive schizotypy. There were diverse patterns of relationship between schizotypal traits and P300 under different oddball conditions, suggesting that characteristics and parameters of target stimuli should be considered cautiously when implementing an auditory oddball paradigm for individuals with schizophrenia spectrum.

The Effects of Total Sleep Deprivation on Attention Capture Processes in Young and Older Adults: An ERP Study

BACKGROUND

The present study investigated whether sleep deprivation affects attention capture in young and older adults using event-related potentials (ERPs).

METHODS

Eleven young adults (20-30 y) and nine older adults (60-70 y) were tested following both normal sleep (NS) and total sleep deprivation (TSD). ERPs were recorded during an auditory discrimination task consisting of standard and deviant stimuli.

RESULTS

Deviant stimuli elicited the MMN, P3a, and RON ERPs. TSD attenuated the differences in reaction times between standards and deviants in young adults but not older adults. The P3a was attenuated in older adults compared to young adults. Older adults had a larger RON amplitude compared to young adults following NS, but not TSD.

CONCLUSIONS

The reduced P3a and the absence of behavioral performance alteration in the older group suggests that older adults may utilize different neural processing strategies compared to younger adults to compensate for age-related declines in neural resources for attention capture. Sleep loss influenced age-related differences on the RON, suggesting that older adults may have reduced access to compensatory strategies following sleep loss.

Unveiling the Associations between EEG Indices and Cognitive Deficits in Schizophrenia-Spectrum Disorders: A Systematic Review

Cognitive dysfunctions represent a core feature of schizophrenia-spectrum disorders due to their presence throughout different illness stages and their impact on functioning. Abnormalities in electrophysiology (EEG) measures are highly related to these impairments, but the use of EEG indices in clinical practice is still limited. A systematic review of articles using Pubmed, Scopus and PsychINFO was undertaken in November 2021 to provide an overview of the relationships between EEG indices and cognitive impairment in schizophrenia-spectrum disorders. Out of 2433 screened records, 135 studies were included in a qualitative review. Although the results were heterogeneous, some significant correlations were identified. In particular, abnormalities in alpha, theta and gamma activity, as well as in MMN and P300, were associated with impairments in cognitive domains such as attention, working memory, visual and verbal learning and executive functioning during at-risk mental states, early and chronic stages of schizophrenia-spectrum disorders. The review suggests that machine learning approaches together with a careful selection of validated EEG and cognitive indices and characterization of clinical phenotypes might contribute to increase the use of EEG-based measures in clinical settings.

Memory-Enhancing Effect of 8-Week Consumption of the Quercetin-Enriched Culinary Herbs-Derived Functional Ingredients: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Due to great demand for memory enhancers, the memory-enhancing effects and the possible underlying mechanisms of the functional ingredients derived from the combined extract of Polygonum odoratum and Morus alba were investigated. A total of 45 participants randomly received either a placebo or the developed herbal supplement at a dose of 50 or 1500 mg/day. The consumption was done once daily for 8 weeks. Working memory was assessed via both an event-related potential and computerized battery tests at baseline and at the end of the 8-week study period. Acetylcholinesterase (AChE) and monoamine oxidase type A and type B (MAO-A, MAO-B) levels were also measured at the end of the study. The subjects who consumed the supplement containing a developed functional ingredient at a dose of 1500 mg/day showed reduced latencies but increased amplitudes of N100 and P300. An improvement in working memory and the suppression of AChE, MAO-A, and MAO-B activities were also observed. Therefore, this study clearly demonstrates the cognitive enhancing effect of the developed herbal congee, which may be associated with the suppressions of AChE and both types of MAO.

The reliability of P300 and the influence of age, gender and education variables in a 50 years and older normative sample

OBJECTIVES

The present study aims to investigate the effects of age, gender, and level of education on P300 in a healthy population, aged 50 years and over; and determine the reliability metrics for different conditions and measurement methods.

METHOD

Auditory and visual oddball recordings of 171 healthy adults were investigated. A fully automated preprocessing was applied to elicit ERP P300. Maximum peak amplitude, latency and mean amplitudes were measured. Data were stratified by age, gender, and education to determine group-level differences by using repeat measures of ANOVA. The internal consistency of P300 was calculated by a split-half method using odd-even segments. Test-retest reliability was assessed by calculating the intraclass correlation coefficient (ICC).

RESULTS

Maximum peak P300 amplitudes were higher in the 50-64 years age group compared to the >65 years age group; and females showed increased P300 amplitudes compared to males. P300 measures showed fair to good internal consistency and poor to good test-retest reliability.

CONCLUSION

Age and gender should be taken into account when designing ERP studies with elderly individuals. P300 showed good internal consistency in general, between gender groups and age groups. Long-term test-retest reliability was lower but acceptable. These findings can be interpreted as the strength of P300 by being an objective and reliable method independent of cultural differences. Here we underline several factors that may affect P300 measures and discuss other possible factors that should be standardized for P300 to be used in clinical settings.

Mismatch Negativity is associated with affective social behavior in microcephaly

Some children with severe microcephaly related to Zika virus infection show affective social-like behavior, such as smiling and rejection to a stranger's lap. Our objective was to check the association between this behavior and the occurrence of Mismatch Response (MMR) in event-related potentials. Twenty eight microcephalic children, aged 1-3 years, were divided in Affect(+) and Affect(-) groups, according to either the presence or absence of affective social-like behavior, respectively, and underwent the OddBall paradigm with vowels as auditory stimuli. MMR was statistically estimated comparing MMR sample means between both groups. The Affect(+) group significantly differed from the Affect(-) group and, as opposed to the latter, showed MMR as Mismatch Negativity (MMN) in the left occipital, left and right posterior temporal, and (especially) the right and median parietal leads. The relationship observed between MMN and affective social-like behavior suggests that these children may have cognitive mechanisms capable of providing some social interaction, despite their profound neurological dysfunction. MMN diagnostic techniques seem to be promising for the triage of microcephalic subjects regarding cognitive functions and for choosing a strategy for some social adaptation.

The age-related changes in 40 Hz Auditory Steady-State Response and sustained Event-Related Fields to the same amplitude-modulated tones in typically developing children: A magnetoencephalography study

Recent studies have revealed that gamma-band oscillatory and transient evoked potentials may change with age during childhood. It is hypothesized that these changes can be associated with a maturation of GABAergic neurotransmission and, subsequently, the age-related changes of excitation-inhibition balance in the neural circuits. One of the reliable paradigms for investigating these effects in the auditory cortex is 40 Hz Auditory Steady-State Response (ASSR), where participants are presented with the periodic auditory stimuli. It is known that such stimuli evoke two types of responses in magnetoencephalography (MEG)-40 Hz steady-state gamma response (or 40 Hz ASSR) and auditory evoked response called sustained Event-Related Field (ERF). Although several studies have been conducted in children, focusing on the changes of 40 Hz ASSR with age, almost nothing is known about the age-related changes of the sustained ERF to the same periodic stimuli and their relationships with changes in the gamma strength. Using MEG, we investigated the association between 40 Hz steady-state gamma response and sustained ERF response to the same stimuli and also their age-related changes in the group of 30 typically developing 7-to-12-year-old children. The results revealed a tight relationship between 40 Hz ASSR and ERF, indicating that the age-related increase in strength of 40 Hz ASSR was associated with the age-related decrease of the amplitude of ERF. These effects were discussed in the light of the maturation of the GABAergic system and excitation-inhibition balance development, which may contribute to the changes in ASSR and ERF.

Hierarchical Classification of Event-Related Potentials for the Recognition of Gender Differences in the Attention Task

Research on the functioning of human cognition has been a crucial problem studied for years. Electroencephalography (EEG) classification methods may serve as a precious tool for understanding the temporal dynamics of human brain activity, and the purpose of such an approach is to increase the statistical power of the differences between conditions that are too weak to be detected using standard EEG methods. Following that line of research, in this paper, we focus on recognizing gender differences in the functioning of the human brain in the attention task. For that purpose, we gathered, analyzed, and finally classified event-related potentials (ERPs). We propose a hierarchical approach, in which the electrophysiological signal preprocessing is combined with the classification method, enriched with a segmentation step, which creates a full line of electrophysiological signal classification during an attention task. This approach allowed us to detect differences between men and women in the P3 waveform, an ERP component related to attention, which were not observed using standard ERP analysis. The results provide evidence for the high effectiveness of the proposed method, which outperformed a traditional statistical analysis approach. This is a step towards understanding neuronal differences between men's and women's brains during cognition, aiming to reduce the misdiagnosis and adverse side effects in underrepresented women groups in health and biomedical research.

Correlates of deviance detection in auditory brainstem responses of bats

Identifying unexpected acoustic inputs, which allows to react appropriately to new situations, is of major importance for animals. Neural deviance detection describes a change of neural response strength to a stimulus solely caused by the stimulus' probability of occurrence. In the present study, we searched for correlates of deviance detection in auditory brainstem responses obtained in anaesthetised bats (Carollia perspicillata). In an oddball paradigm, we used two pure tone stimuli that represented the main frequencies used by the animal during echolocation (60 kHz) and communication (20 kHz). For both stimuli, we could demonstrate significant differences of response strength between deviant and standard response in slow and fast components of the auditory brainstem response. The data suggest the presence of correlates of deviance detection in brain stations below the IC, at the level of the cochlea nucleus and lateral lemniscus. Additionally, our results suggest that deviance detection is mainly driven by repetition suppression in the echolocation frequency band, while in the communication band, a deviant-related enhancement of the response plays a more important role. This finding suggests a contextual dependence of the mechanisms underlying subcortical deviance detection. The present study demonstrates the value of auditory brainstem responses for studying deviance detection and suggests that auditory specialists, such as bats, use different frequency-specific strategies to ensure an appropriate sensation of unexpected sounds.

Memory Clinics and Day Care Centers in Thessaloniki, Northern Greece: 30 Years of Clinical Practice and Experience

Background: This review describes the diagnostic and interventional procedures conducted in two university memory clinics (established network of G. Papanikolaou Hospital: 1988–2017 and AHEPA hospital: 2017–today) and 2 day care centers (established network of DCCs: 2005–today) in North Greece and their contribution in the scientific field of dementia. The aims of this work are (1) to provide a diagnosis and treatment protocol established in the network of memory clinics and DCCs and (2) to present further research conducted in the aforementioned network during the last 30 years of clinical practice.

Methods: The guidelines to set a protocol demand a series of actions as follows: (1) set the diagnosis criteria, neuropsychological assessment, laboratory examinations, and examination of neurophysiological, neuroimaging, cerebrospinal fluid, blood, and genetic markers; and (2) apply non-pharmacological interventions according to the needs and specialized psychosocial interventions of the patient to the caregivers of the patient.

Results: In addition to the guidelines followed in memory clinics at the 1st and 3rd Department of Neurology and two DCCs, a database of patients, educational programs, and further participation in international research programs, including clinical trials, make our contribution in the dementia field strong.

Conclusion: In the current paper, we provide useful guidelines on how major and minor neurocognitive disorders are being treated in Thessaloniki, Greece, describing successful practices which have been adapted in the last 30 years.

β-Lactolin Enhances Neural Activity, Indicated by Event-Related P300 Amplitude, in Healthy Adults: A Randomized Controlled Trial

Background:

Epidemiological studies have shown that dairy product consumption is beneficial for cognitive function in elderly individuals. β-lactolin is a Gly–Thr–Trp–Tyr lacto-tetrapeptide rich in fermented dairy products that improves memory retrieval, attention, and executive function in older adults with subjective cognitive decline and prevents the pathology of Alzheimer’s disease in rodents. There has been no study on the effects of β-lactolin on neural activity in humans.

Objective:

We investigated the effects of β-lactolin on neural activity and cognitive function in healthy adults.

Methods:

In this randomized, double-blind, placebo-controlled study, 30 participants (45–64 years old) consumed β-lactolin or placebo for 6 weeks. Neural activity during auditory and language tasks was measured through 64-channel electroencephalography. Moreover, verbal fluency tests were performed at baseline and after 6 weeks.

Results:

The β-lactolin group had a significantly higher P300 amplitude at the Cp2 site (a part of the parietal lobe near the center of brain, p = 0.011), and C4 site (the area between the frontal and parietal lobe, p = 0.02) during the auditory tasks after 6 weeks than the placebo group. Thus, β-lactolin supplementation promoted neural activity in the parietal area, which increases concentration and attention during auditory cognitive tasks. Compared with the placebo group, the β-lactolin group also showed significant changes in the scores of verbal fluency test after 6 weeks (p = 0.033).

Conclusion:

Our findings provide insight into the mechanisms underlying the effects of β-lactolin on attention in healthy adults.

Differential effects of gender on mismatch negativity to violations of simple and pattern acoustic regularities

INTRODUCTION

The effects of gender on the mismatch negativity (MMN) potential have been studied using simple frequency deviants. However, the effects of gender on MMN to violations of abstract regularities have not yet been studied. Here, we addressed this issue and compared the effects of gender on simple and pattern frequency MMNs.

METHODS

MMN response was recorded from 29 healthy young adults, 14 females (mean age = 26.20 ± 2.17) and 15 males (mean age = 27.57 ± 2.24), using 32 scalp electrodes during simple and pattern frequency oddball paradigms and the mean amplitude, peak latency, and scalp topography of MMN evoked by each paradigm were compared between the two genders.

RESULTS

The peak latency of simple MMN was significantly longer in females (p < .05); however, its mean amplitude and topography were similar between the two genders (p > .05). There were no significant differences in peak latency, mean amplitude, and scalp topography of pattern MMN between the two genders (p > .05).

CONCLUSIONS

Based on the obtained results, gender differently affects simple and pattern MMN. These findings may provide preliminary evidence for distinct effects of gender on various types of MMN.

Effects of Amateur Musical Experience on Categorical Perception of Lexical Tones by Native Chinese Adults: An ERP Study

Music impacting on speech processing is vividly evidenced in most reports involving professional musicians, while the question of whether the facilitative effects of music are limited to experts or may extend to amateurs remains to be resolved. Previous research has suggested that analogous to language experience, musicianship also modulates lexical tone perception but the influence of amateur musical experience in adulthood is poorly understood. Furthermore, little is known about how acoustic information and phonological information of lexical tones are processed by amateur musicians. This study aimed to provide neural evidence of cortical plasticity by examining categorical perception of lexical tones in Chinese adults with amateur musical experience relative to the non-musician counterparts. Fifteen adult Chinese amateur musicians and an equal number of non-musicians participated in an event-related potential (ERP) experiment. Their mismatch negativities (MMNs) to lexical tones from Mandarin Tone 2–Tone 4 continuum and non-speech tone analogs were measured. It was hypothesized that amateur musicians would exhibit different MMNs to their non-musician counterparts in processing two aspects of information in lexical tones. Results showed that the MMN mean amplitude evoked by within-category deviants was significantly larger for amateur musicians than non-musicians regardless of speech or non-speech condition. This implies the strengthened processing of acoustic information by adult amateur musicians without the need of focused attention, as the detection of subtle acoustic nuances of pitch was measurably improved. In addition, the MMN peak latency elicited by across-category deviants was significantly shorter than that by within-category deviants for both groups, indicative of the earlier processing of phonological information than acoustic information of lexical tones at the pre-attentive stage. The results mentioned above suggest that cortical plasticity can still be induced in adulthood, hence non-musicians should be defined more strictly than before. Besides, the current study enlarges the population demonstrating the beneficial effects of musical experience on perceptual and cognitive functions, namely, the effects of enhanced speech processing from music are not confined to a small group of experts but extend to a large population of amateurs.

Effect of Quiet and Noise on P300 Response in Individuals with Auditory Neuropathy Spectrum Disorder

Introduction  Auditory neuropathy spectrum disorder (ANSD) is a clinical condition in which individuals have normal cochlear responses and abnormal neural responses. There is a lack of evidence in the literature regarding the neural discrimination skill in individuals with ANSD, especially when the signal is presented in the presence of noise. Objectives  The present study was performed with the aim to investigate auditory discrimination skill, in quiet and in the presence of noise, in individuals with ANSD and to compare the findings with normal-hearing individuals. Methods  A total of 30 individuals with normal hearing sensitivity and 30 individuals with ANSD in the age range of 15 to 55 years old, with the mean age of 27.86 years old, were the participants. P300 response was recorded from both groups using syllable pairs /ba/-/da/ in oddball paradigm and the syllable /da/ in repetitive paradigm in quiet and at +10 dB signal-to-noise ratio (SNR). Results  There was significant prolongation in latency and reaction time, and reduction in amplitude of P300 response and sensitivity in both groups with the addition of noise. The topographic pattern analysis showed activation of the central-parietal-occipital region of the brain in individuals with ANSD, whereas activation of the central-parietal region was observed in individuals with normal hearing. The activation was more diffused in individuals with ANSD compared with that of individuals with normal hearing. Conclusion  The individuals with ANSD showed a significantly more adverse effect of noise on the neural discrimination skill than the normal counterpart.

Perceptual and Electrophysiological Correlates of Fixed Versus Moving Sound Source Lateralization

Purpose The aims of the study were (a) to evaluate the effects of systematically varied factors of stimulus duration, interaural-level difference (ILD), and direction on perceptual and electrophysiological metrics of lateralization for fixed versus moving targets and (b) to evaluate the hemispheric activity underlying perception of fixed versus moving auditory targets. Method Twelve normal-hearing, young adult listeners were evaluated using perceptual and P300 tests of lateralization. Both perceptual and P300 tests utilized stimuli that varied for type (fixed and moving), direction (right and left), duration (100 and 500 ms), and magnitude of ILD (9 and 18 dB). Listeners provided laterality judgments and stimulus-type discrimination (fixed vs. moving) judgments for all combinations of acoustic factors. During P300 recordings, listeners discriminated between left- versus right-directed targets, as the other acoustic parameters were varied. Results ILD magnitude and stimulus type had statistically significant effects on laterality ratings, with larger magnitude ILDs and fixed type resulting in greater lateralization. Discriminability between fixed versus moving targets was dependent on stimulus duration and ILD magnitude. ILD magnitude was a significant predictor of P300 amplitude. There was a statistically significant inverse relationship between the perceived velocity of targets and P300 latency. Lateralized targets evoked contralateral hemispheric P300 activity. Moreover, a right-hemisphere enhancement was observed for fixed-type lateralized deviant stimuli. Conclusions Perceptual and P300 findings indicate that lateralization of auditory movement is highly dependent on temporal integration. Both the behavioral and physiological findings of this study suggest that moving auditory targets with ecologically valid velocities are processed by the central auditory nervous system within a window of temporal integration that is greater than that for fixed auditory targets. Furthermore, these findings lend support for a left hemispatial perceptual bias and right hemispheric dominance for spatial listening.

Design and evaluation of the effectiveness of a corpus of congruent and incongruent English sentences for the study of event related potentials

OBJECTIVE

To design and evaluate the effectiveness of a stimulus material in eliciting the N400 event related potential (ERP).

DESIGN

A set of 700 semantically congruent and incongruent sentences was developed in accordance with current linguistic norms, and validated with an electroencephalography (EEG) study, in which the influence of age and gender on the N400 ERP magnitude was analysed.

STUDY SAMPLE

Forty-five normal-hearing subjects (19-57 years, 21 females) participated in the EEG study.

RESULTS

The stimulus material used in the EEG study elicited a robust N400 ERP, with a morphology consistent with the literature. Results also showed no statistically significant effect of age or gender on the N400 magnitude.

CONCLUSIONS

The material presented in this paper constitutes the largest complete stimulus set suitable for both auditory and text-based N400 experiments. This material may help facilitate the efficient implementation of future N400 ERP studies, as well as promote standardisation and consistency across studies.

P300 Event-Related Potentials in Normal-Hearing Adults With Type 2 Diabetes Mellitus

Background P300 event-related potentials can be used to measure auditory processing speed, working memory, and attention. Purpose The purpose of the study was to compare P300 event-related potentials in normal-hearing adults with those of adults with Type II diabetes mellitus. Research Design A two-group (with diabetes and controls) comparative study (age- and sex-matched) with a nonprobability sampling method was used. Study Sample Sixty-four adult participants (32 with diabetes, 32 without diabetes) between the ages of 23 and 60 years participated. Data Collection and Analysis Pure-tone audiometry was performed to ensure participants had pure-tone averages of ≤ 25 dB HL. Folstein Mini-Mental State Examinations were conducted, which ensured absence of cognitive impairment. Blood glucose levels were measured immediately prior to P300 testing, after which amplitude and latency results were captured. Descriptive analysis was used to calculate mean, standard deviation, median, and 25th and 75th percentiles. To study differences between adults with and without diabetes as well as the effect of glucose, linear mixed-model regression analyses were performed when left and right ears were combined, and simple linear regression analyses were performed when left and right ears were analyzed separately. Results For P300 latency results, a significant statistical difference (p < .001) was observed between participants with and without diabetes (352.46 ms, SD = 36.36; 314.09 ms, SD = 32.08), respectively. A significant statistical difference (p < .001) in amplitude was observed between participants with and without diabetes, respectively (12.10 μV, SD = 3.70; 15.08 μV, SD = 2.82). Glucose was a key moderator of only amplitude after adjusting for diabetes status. Glucose had no effect on amplitude and latency for adults without Type II diabetes mellitus (DM). Conclusions Type II DM decreases amplitude and increases latency; in addition, adults with Type II DM, attention, and working memory, as denoted by P300 amplitude, may deteriorate with increased glucose levels on the day of testing.

Language-Related Brain Potentials in Patients With Disorders of Consciousness: A Follow-up Study to Detect “Covert” Language Disorders

Background. Language disorders may occur in patients with disorders of consciousness (DoCs), and they could interfere with the behavioral assessment of consciousness and responsiveness. Objective. In this study, we retrospectively explored whether ERP N400 was eventually associated with the presence of aphasia diagnosed in those patients who had evolved into Exit-Minimally Conscious State (E-MCS) at the clinical follow-up. Methods. In this retrospective cohort study, the ERPs elicited by an auditory sentences task were retrospectively examined in a sample of 15 DoC patients diagnosed according to the Coma Recovery Scale–Revised (CRS-R). All these 15 DoC patients underwent a (at least) 1-year clinical follow-up, which included a neuropsychological evaluation to assess language function among other cognitive functions. Ten healthy individuals also underwent the same paradigm to investigate the variability of ERPs characteristics. Results. The N400 ERP component with centroparietal topography was found in 9 of 10 healthy controls in response to the ill-formed sentences. Analysis of patients’ data revealed that (1) a significant N400 component could be detected in 64% (9 of 14 patients) of the DoC patients regardless of the type of DoC; (2) no significant N400 ERP component was retrospectively detected in those E-MCS patients who showed aphasia at the follow-up; and (3) the presence/absence of the N400-ERP component was consistent with the brain lesion side and significantly predict the recovery. Conclusion. These preliminary findings indicate that the absence of N400 was significantly associated with the presence of aphasia diagnosed at the clinical follow-up in E-MCS patients.

Trial-by-trial surprise-decoding model for visual and auditory binary oddball tasks

Having to survive in a continuously changing environment has driven the human brain to actively predict the future state of its surroundings. Oddball tasks are specific types of experiments in which this nature of the human brain is studied. Detailed mathematical models have been constructed to explain the brain's perception in these tasks. These models consider a subject as an ideal observer who abstracts a hypothesis from the previous stimuli, and estimates its hyper-parameters - in order to make the next prediction. The corresponding prediction error is assumed to manifest the subjective surprise of the brain. While the approach of earlier works to this problem has been to suggest an encoding model, we investigated the reverse model: if the stimuli's surprise is assumed as the cause of the observer's surprise, it must be possible to decode the surprise of each stimulus, for every single subject, given only their neural responses, i.e. to tell how unexpected a specific stimulus has been for them. Employing machine learning tools, we developed a surprise decoding model for binary oddball tasks. We constructed our model using the ideal observer proposed by Meyniel et al. in 2016, and applied it to three datasets, one with visual, one with auditory, and one with both visual and auditory stimuli. We demonstrated that our decoding model performs very well for both of the sensory modalities with or without the presence of the subject's motor response.

Multi-Resolution Graph Based Volumetric Cortical Basis Functions From Local Anatomic Features

OBJECTIVE

Modern clinical MRI collects millimeter scale anatomic information, but scalp electroencephalography source localization is ill posed, and cannot resolve individual sources at that resolution. Dimensionality reduction in the space of cortical sources is needed to improve computational and storage complexity, yet volumetric methods still employ simplistic grid coarsening that eliminates fine scale anatomic structure. We present an approach to extend near-arbitrary spatial scaling to volumetric localization.

METHODS

Starting from a voxelwise brain parcellation, sub-parcels are identified from local cortical connectivity with an iterated graph cut approach. Spatial basis functions in each parcel are constructed using either a decomposition of the local leadfield matrix or spectral basis functions of local cortical connectivity graphs.

RESULTS

We present quantitative evaluation with extensive simulations and use multiple sets of real data to highlight how parameter changes impact computed reconstructions. Our results show that volumetric basis functions can improve accuracy by as much as 30%, while reducing computational complexity by over two orders of magnitude. In real data from epilepsy surgical candidates, accurate localization of seizure onset regions is demonstrated.

CONCLUSION

Spatial dimensionality reduction with volumetric basis functions improves reconstruction accuracy while reducing computational complexity.

SIGNIFICANCE

Near-arbitrary spatial dimensionality reduction will enable volumetric reconstruction with modern computationally intensive algorithms and anatomically driven multi-resolution methods.

Effects of Gender and Apolipoprotein E on Novelty MMN and P3a in Healthy Elderly and Amnestic Mild Cognitive Impairment

Background: The apolipoprotein E epsilon4 (ApoE ε4) allele and female gender may be important risk factors for the development of Alzheimer’s disease and amnestic mild cognitive impairment (aMCI). Novelty mismatch negativity (MMN) represents the pre-attentive index of deviance detection and P3a represents the attention orienting response. Furthermore, MMN and P3a components have been reported to be potential markers in aMCI. Therefore, this study will investigate the effects of gender and ApoE on auditory novelty MMN and P3a and their relationship to neuropsychological performance in aMCI.

Methods: Thirty nine aMCI subjects and 44 controls underwent neuropsychological assessment and ApoE genotyping. Novelty MMN and P3a components were investigated during an auditory novelty oddball task.

Results: Firstly, novelty MMN latency was significantly shorter in aMCI than in healthy control (HC) group. Secondly, novelty MMN latency was negatively correlated with episodic memory in aMCI, but not in HC. Novelty P3a latency was negatively correlated with information processing speed in all subjects. For gender effect, novelty MMN latency was shorter in aMCI females than in HC females. Moreover, novelty P3a amplitudes were lower in males than in females in both aMCI and HC. For the effect of ApoE status, novelty MMN latency was shorter in aMCI ApoE ε4- than HC ApoE ε4-.

Conclusion: aMCI presents altered pre-attentive processing indexed by novelty MMN components. Furthermore, there may be a compensatory mechanism on the impaired processing in aMCI. It further suggests that aMCI female and ApoE ε4- recruited the compensatory mechanism.

Gender effects on auditory P300: A systematic review

The evidence suggests that gender-related effects could influence the electrophysiological P300 parameters and stand as an additional source of variation for both clinical and non-clinical subjects. The aim of this paper is to characterize gender-related differences in P300 potential as elicited with simple auditory paradigms. This knowledge (1) is important for the practical assessment of P300 potential in normal and clinical populations, and (2) can provide an insight into the understanding of gender differences in pathophysiology, particularly those with differential risk or prevalence in males and females. With this review it is shown that a limited number of studies encounter possible gender effects on parameters of auditory P300, and the findings need to be read with caution due to methodological limitations of the studies. Nevertheless, evidence supports that the P300 amplitude could be significantly modulated by gender, with greater amplitude in females relative to males. Noteworthy, gender has a minimal effect on the P300 latency, and it is often comparable between males and females. Furthermore, the effect of gender on P300 could be modulated by hormonal background, anatomy and some methodological aspects.

Can a Novel High-Density EEG Approach Disentangle the Differences of Visual Event Related Potential (N170), Elicited by Negative Facial Stimuli, in People with Subjective Cognitive Impairment?

BACKGROUND

Studies on subjective cognitive impairment (SCI) and neural activation report controversial results.

OBJECTIVE

To evaluate the ability to disentangle the differences of visual N170 ERP, generated by facial stimuli (Anger & Fear) as well as the cognitive deterioration of SCI, mild cognitive impairment (MCI), and Alzheimer's disease (AD) compared to healthy controls (HC).

METHOD

57 people took part in this study. Images corresponding to facial stimuli of "Anger" and "Fear" were presented to 12 HC, 14 SCI, 17 MCI and 14 AD participants. EEG data were recorded by using a HD-EEG HydroCel with 256 channels.

RESULTS

Results showed that the amplitude of N170 can contribute in distinguishing the SCI group, since statistically significant differences were observed with the HC (p < 0.05) and the MCI group from HC (p < 0.001), as well as AD from HC (p = 0.05) during the processing of facial stimuli. Noticeable differences were also observed in the topographic distribution of the N170 amplitude, while localization analysis by using sLORETA images confirmed the activation of superior, middle-temporal, and frontal lobe brain regions. Finally, in the case of "Fear", SCI and HC demonstrated increased activation in the orbital and inferior frontal gyrus, respectively, MCI in the inferior temporal gyrus, and AD in the lingual gyrus.

CONCLUSION

These preliminary findings suggest that the amplitude of N170 elicited after negative facial stimuli could be modulated by the decline related to pathological cognitive aging and can contribute in distinguishing HC from SCI, MCI, and AD.

Application of the P300 Event-Related Potential in the Diagnosis of Epilepsy Disorder: A Review

Epilepsy is one of the most serious chronical neurological disorders, affecting more than 50 million people worldwide. It can be defined as a spectrum disorder, and patients with epilepsy possess abnormalities in cognitive functions. A number of factors can cause cognitive dysfunctions in epileptic syndromes, including etiology, the age of onset, type of seizure and severity, duration, and antiepileptic drugs. Event-related potentials (ERPs) are very useful clinical and research instruments to evaluate cognitive function in patients with neuropsychiatry disorders. Event-related potentials directly reflect cortical neuronal activity and provide a particular level of temporal resolution. Among various ERP components, the P300 is the most important component for assessing cognitive processes such as attention, working memory, and concentration. Numerous studies have reported the abnormalities in amplitude or latency of P300 component of ERP in epileptic patients, and these abnormalities are indicative of cognitive dysfunction. Therefore, the purpose of this review is to consolidate the existing literature in connection with the use of P300 in epileptic patients.

On the use of the P300 as a tool for cognitive processing assessment in healthy aging: A review

Changes in patterns of performance for the cognitive functions of memory, processing speed, and focused attention are expected in old age.

Differences in Cortical Sources of the Event-Related P3 Potential Between Young and Old Participants Indicate Frontal Compensation

The event-related P3 potential, as elicited in auditory signal detection tasks, originates from neural activity of multiple cortical structures and presumably reflects an overlap of several cognitive processes. The fact that the P3 is affected by aging makes it a potential metric for age-related cognitive change. The P3 in older participants is thought to encompass frontal compensatory activity in addition to task-related processes. The current study investigates this by decomposing the P3 using group independent component analysis (ICA). Independent components (IC) of young and old participants were compared in order to investigate the effects of aging. Exact low-resolution tomography analysis (eLORETA) was used to compare current source densities between young and old participants for the P3-ICs to localize differences in cortical source activity for every IC. One of the P3-related ICs reflected a different constellation of cortical generators in older participants compared to younger participants, suggesting that this P3-IC reflects shifts in neural activations and compensatory processes with aging. This P3-IC was localized to the orbitofrontal/temporal, and the medio-parietal regions. For this IC, older participants showed more frontal activation and less parietal activation as measured on the scalp. The differences in cortical sources were localized in the precentral gyrus and the parahippocampal gyrus. This finding might reflect compensatory activity recruited from these cortical sources during a signal detection task.

Sentence Context Prevails Over Word Association in Aphasia Patients with Spared Comprehension: Evidence from N400 Event-Related Potential

Behavioral and event-related potential (ERP) studies on aphasia patients showed that lexical information is not lost but rather its integration into the working context is hampered. Studies have been conducted on the processing of sentence-level information (meaningful versus meaningless) and of word-level information (related versus unrelated) in aphasia patients, but we are not aware of any study that assesses the relationship between the two. In healthy subjects the processing of a single word in a sentence context has been studied using the N400 ERP. It was shown that, even when there is only a weak expectation of a final word in a sentence, this expectation will dominate word relatedness. In order to study the effect of semantic relatedness between words in sentence processing in aphasia patients, we conducted a crossed-design ERP study, crossing the factors of word relatedness and sentence congruity. We tested aphasia patients with mild to minimum comprehension deficit and healthy young and older (age-matched with our patients) controls on a semantic anomaly judgment task when simultaneously recording EEG. Our results show that our aphasia patient’s N400 amplitudes in response to the sentences of our crossed-design study were similar to those of our age-matched healthy subjects. However, we detected an increase in the N400 ERP latency in those patients, indicating a delay in the integration of the new word into the working context. Additionally, we observed a positive correlation between comprehension level of those patients and N400 effect in response to meaningful sentences without word relatedness contrasted to meaningless sentences without word relatedness.

Influence of sex on P300: an event-related potential electrophysiological study

The primary objective of this study was to further characterize the role of sex, if any, in event-related potentials (ERPs). More specifically, we aimed to investigate sex sensitivity with respect to the P300 ERP. Each female and male study participant underwent an oddball paradigm electroencephalography ERP session. ERP data were subjected to preprocessing and postprocessing, as well as statistical analysis. The results of the study showed that men had larger P300 amplitudes on average for both low-probability and high-probability stimuli compared with women (P<0.001). Men also showed shorter P300 latencies on average than did women (P<0.001). Significant differences in ERPs between men and women were observed in this study. The results indicate the existence of sex sensitivity to the P300 ERP, which may be because of men eliciting higher response inhibition compared with women.

A multi-resolution approach to localize neural sources of P300 event-related brain potential

BACKGROUND AND OBJECTIVE

P300 is probably the most well-known component of event-related brain potentials (ERPs). Using an oddball paradigm, a P300 component can be identified, that is, elicited by the target stimuli recognition. Since P300 is associated with attention and memory operations of the brain, investigation of this component can improve our understanding of these mechanisms. The present study is aimed at identifying the P300 generators in 30 healthy subjects aged 18-30 years using time-reduction region-suppression linearly constrained minimum variance (TR-LCMV) beamformer.

METHODS

In our study, TR-LCMV beamformer with multi-resolution approach is proposed, coarse-resolution space to find the approximated coherent source locations, fine-resolution space to estimate covariance matrix for dimension reduction of determined regions, and normal-resolution space to localize the P300 generators in the brain.

RESULTS

Our results over simulated and real data showed that this approach is a suitable tool to the analysis of ERP fields with localizing superior and inferior frontal lobe, middle temporal gyrus, parietal lobe, and cingulate gyrus as the most prominent sources of P300. The result of P300 localization was finally compared with the other localization methods and it is demonstrated that enhanced performance is achieved.

CONCLUSIONS

Our results showed that the P300 originates from a widespread neuronal network in the brain and not from a specific region. Our finding over simulated and real data demonstrated the ability of the TR-LCMV algorithm for P300 source localization.

Modulation of neurophysiological auditory processing measures by bilateral transcranial direct current stimulation in schizophrenia

This study used bilateral transcranial direct current stimulation (tDCS) to target neural generators of auditory Mismatch Negativity (MMN) and oddball P300 in schizophrenia patients. tDCS was applied to the pre-frontal cortex in a parallel between-group design. There was a significant main effect of stimulation resulting in modulation of MMN amplitude. This effect was mainly driven by a non-significant, but large, effect-size decrease in MMN amplitude with anodal stimulation. This is the first study to demonstrate that tDCS is able to engage and modulate an EEG-based auditory processing measure in schizophrenia.

EEG Recorded from the Ear: Characterizing the Ear-EEG Method

Highlights

Auditory middle and late latency responses can be recorded reliably from ear-EEG.

For sources close to the ear, ear-EEG has the same signal-to-noise-ratio as scalp.

Ear-EEG is an excellent match for power spectrum-based analysis.

A method for measuring electroencephalograms (EEG) from the outer ear, so-called ear-EEG, has recently been proposed. The method could potentially enable robust recording of EEG in natural environments. The objective of this study was to substantiate the ear-EEG method by using a larger population of subjects and several paradigms. For rigor, we considered simultaneous scalp and ear-EEG recordings with common reference. More precisely, 32 conventional scalp electrodes and 12 ear electrodes allowed a thorough comparison between conventional and ear electrodes, testing several different placements of references. The paradigms probed auditory onset response, mismatch negativity, auditory steady-state response and alpha power attenuation. By comparing event related potential (ERP) waveforms from the mismatch response paradigm, the signal measured from the ear electrodes was found to reflect the same cortical activity as that from nearby scalp electrodes. It was also found that referencing the ear-EEG electrodes to another within-ear electrode affects the time-domain recorded waveform (relative to scalp recordings), but not the timing of individual components. It was furthermore found that auditory steady-state responses and alpha-band modulation were measured reliably with the ear-EEG modality. Finally, our findings showed that the auditory mismatch response was difficult to monitor with the ear-EEG. We conclude that ear-EEG yields similar performance as conventional EEG for spectrogram-based analysis, similar timing of ERP components, and equal signal strength for sources close to the ear. Ear-EEG can reliably measure activity from regions of the cortex which are located close to the ears, especially in paradigms employing frequency-domain analyses.