Prestimulus EEG alpha phase synchronicity influences N100 amplitude and reaction time

The influence of the level of prestimulus alpha phase synchronicity on the N100 component and reaction time (RT) was examined, in target auditory oddball data from 25 normal subjects. Alpha phase synchronicity is a new measure consisting (for a given stimulus presentation) of the angular or circular variance of the alpha phase at stimulus onset across the parieto-occipital sites. The lower the angular variance, the higher the phase synchronicity (the more closely in phase the alpha activity across these sites) and vice versa. Subaveraged event-related potentials (ERPs) were formed for high and low prestimulus alpha phase synchronicity stimulus presentations. N100 amplitude was significantly greater in the high than the low phase synchronicity subaverages. In addition, RT was significantly reduced in the high prestimulus alpha phase synchronicity cases. Alpha phase synchronicity reflects an aspect of brain state that influences subsequent stimulus processing.     

ERP and pupil responses to deviance in an oddball paradigm

We investigated the relationship between, and functional significance of, P300, novelty P3, and the pupil dilation response (PDR). Subjects categorized stimuli including (a) words of a frequent category, (b) words of an infrequent category (14%), and (c) pictures of the frequent category (“novels”; 14%). The P300 and novelty P3 were uncorrelated with the PDR and differed in their response to experimental manipulation. Therefore, although the three physiological responses often co‐occur, they appear to each manifest a distinct function: The PDR may be more closely linked to aspects of behavioral responding than the event‐related potentials. Within participants, P300 and PDR latencies accounted for unique portions of the reaction time variance, and amplitudes of all three responses were larger for stimuli recalled on a subsequent test, compared to not recalled. We discuss the possibility that all three responses reflect norepinephric input from the locus coeruleus.     

Evoked activity and EEG phase resetting in the genesis of auditory Go/NoGo ERPs

Current views of the genesis of the event-related potential (ERP) contrast the phase-reset and evoked activity models. In the former, a portion of the ongoing electroencephalographic (EEG) activity becomes phase-locked at stimulus onset; in the latter, processing in the brain contributes additional time-locked activity at each trial. This study aimed to explore these perspectives in an auditory Go/NoGo task. The interactions between these processes were examined using the amplitudes and topographies of pre- and post-stimulus EEGs in traditional bands, and the averaged ERPs, together with time-frequency analysis. Results indicate that both evoked activity and phase locking of ongoing EEG activity contribute substantially to the different Go and NoGo ERP components. Phase locking contributes most strongly to the early exogenous ERP components, with evoked brain activity related to cognitive processing contributing strongly to the endogenous ERP components. Evidence also suggests that extensive phase realignments may generate the power increases associated with early exogenous components. It is concluded that exogenous ERP components arise substantially from phase-resetting mechanisms involving ongoing EEG activity. In contrast, the endogenous components are substantially produced by evoked activity in various frequency bands, and their differences reflect differential cortical processing required for appropriate responding to the Go vs. NoGo stimuli.     

Single-trial event-related potentials and autonomic measures of the orienting reflex

We aimed to clarify the event-related potentials (ERPs) associated with elicitation and habituation of the basic Orienting Reflex (OR). Participants were presented with 16 innocuous tones, alternating in intensity, at long variable inter-stimulus intervals, with no task. This allowed us to examine stimulus novelty and intensity effects in the absence of stimulus-related task demands. Single-trial ERPs were extracted to obtain estimates of the early N1 and the late positive complex (LPC) to each stimulus. Electrodermal responses showed substantial main effects of trials and intensity, supporting their functionality as an OR index. Cardiac deceleration showed no systematic change with intensity or trials, suggesting that it marks the transient onset of each stimulus, early in the stimulus-processing sequence. Respiratory pause showed a substantial main effect of trials but no intensity effect, suggesting that it reflects an intermediate processing stage. A main effect of intensity, but no simple trial effect, was apparent in the N1, suggesting that it reflects a different intermediate processing stage. The subsequent LPC showed only a topographic interaction with trials and intensity, failing to support any substantive role in OR processing. These different stimulus-response profiles are discussed in the context of a sequential processing model of the OR.     

The component structure of ERP subsequent memory effects in the Von Restorff paradigm and the word frequency effect in recall

We examined the degree to which ERP components elicited by items that are isolated from their context, either by their font size (“size isolates”) or by their frequency of usage, are correlated with subsequent immediate recall. Study lists contained (a) 15 words including a size isolate, (b) 14 high frequency (HF) words with one low frequency word (“LF isolate”), or (c) 14 LF words with one HF word. We used spatiotemporal PCA to quantify ERP components. We replicated previously reported P300 subsequent memory effects for size isolates and found additional correlations with recall in the novelty P3, a right lateralized positivity, and a left lateralized slow wave that was distinct from the slow wave correlated with recall for nonisolates. LF isolates also showed evidence of a P300 subsequent memory effect and also elicited the left lateralized subsequent memory effect, supporting a role of distinctiveness in word frequency effects in recall.     

Validation of ICA as a tool to remove eye movement artifacts from EEG/ERP

Eye movement artifacts in electroencephalogram (EEG) recordings can greatly distort grand mean event‐related potential (ERP) waveforms. Different techniques have been suggested to remove these artifacts prior to ERP analysis. Independent component analysis (ICA) is suggested as an alternative method to “filter” eye movement artifacts out of the EEG, preserving the brain activity of interest and preserving all trials. However, the identification of artifact components is not always straightforward. Here, we compared eye movement artifact removal by ICA compiled on 10 s of EEG, on eye movement epochs, or on the complete EEG recording to the removal of eye movement artifacts by rejecting trials or by the Gratton and Coles method. ICA performed as well as the Gratton and Coles method. By selecting only eye movement epochs for ICA compilation, we were able to facilitate the identification of components representing eye movement artifacts.     

Demonstrating emotional processing differences in psychopathy using affective ERP modulation

Psychopaths exhibit abnormalities processing emotional information, but there is less certainty regarding the role attention plays in these processes. We present data from two affective picture‐viewing tasks comparing event‐related potential (ERP) modulation effects when emotional information is present but not task relevant (Task 1) followed by a condition directing attention to the categorization of emotional content (Task 2). Controls show a robust, persistent ERP positivity (200–900 ms) associated with emotional target photos compared to neutral targets in both tasks. Individuals with psychopathy only showed this differentiation when explicitly attending to the emotional content of the photos (Task 2), and these effects remained smaller than the amplitude differences demonstrated by controls. Although abnormal allocation of attention may play a critical role, this cannot completely account for emotional processing deficits associated with psychopathy.     

EEG frequency PCA in EEG‐ERP dynamics

Principal components analysis (PCA) has long been used to decompose the ERP into components, and these mathematical entities are increasingly accepted as meaningful and useful representatives of the electrophysiological components constituting the ERP. A similar expansion appears to be beginning in regard to decomposition of the EEG amplitude spectrum into frequency components via frequency PCA. However, to date, there has been no exploration of the brain's dynamic EEG‐ERP linkages using PCA decomposition to assess components in each measure. Here, we recorded intrinsic EEG in both eyes‐closed and eyes‐open resting conditions, followed by an equiprobable go/no‐go task. Frequency PCA of the EEG, including the nontask resting and within‐task prestimulus periods, found seven frequency components within the delta to beta range. These differentially predicted PCA‐derived go and no‐go N1 and P3 ERP components. This demonstration suggests that it may be beneficial in future brain dynamics studies to implement PCA for the derivation of data‐driven components from both the ERP and EEG.     

The neurophysiological bases of EEG and EEG measurement: A review for the rest of us

A thorough understanding of the EEG signal and its measurement is necessary to produce high quality data and to draw accurate conclusions from those data. However, publications that discuss relevant topics are written for divergent audiences with specific levels of expertise: explanations are either at an abstract level that leaves readers with a fuzzy understanding of the electrophysiology involved, or are at a technical level that requires mastery of the relevant physics to understand. A clear, comprehensive review of the origin and measurement of EEG that bridges these high and low levels of explanation fills a critical gap in the literature and is necessary for promoting better research practices and peer review. The present paper addresses the neurophysiological source of EEG, propagation of the EEG signal, technical aspects of EEG measurement, and implications for interpretation of EEG data.     

Trial effects in single-trial ERP components and autonomic responses at very long ISIs

Single-trial data from autonomic and ERP measures were used to capture the rapidly decreasing initial responses characteristic of the orienting reflex (OR) to repeated stimuli. Stimulus–response patterns were compared to determine central analogues of autonomic indices of processes leading to the OR, and the OR itself. Participants were presented with 12 indifferent tones in an auditory dishabituation paradigm. Temporal principal component analysis (PCA) decomposed EOG-corrected ERP data for 16 subjects. Response patterns of ERPs, cardiac, and respiratory responses were compared to the phasic skin conductance response (SCR). SCR decremented over trials, recovered on the change trial, and dishabituated to the representation of the standard, meeting the formal definition of habituation required of the OR. The evoked cardiac response showed no trial effects. Respiratory pause (RP) decreased linearly over trials, recovering marginally on the change trial. Nine identifiable ERP components were extracted: P1, N1-3, N1-1, processing negativity (PN), P2, P3a, P3b, a novelty-sensitive P3 component (labelled HabP3), and the slow wave (SW). P3b and SW showed decrement over trials, but with no recovery, HabP3 showed decrement and increased response on the change trial, while the P1, N1 subcomponents, P2 and P3a were insensitive to novelty. Stimulus–response patterns of the RP and HabP3 suggest sensitivity to novelty processing, while the P1, N1-3, N-1, PN, P2, P3a and cardiac deceleration appear to mark processing prior to novelty, such as stimulus transient detection (cardiac deceleration) and/or intensity processing. This study supports predictions of preliminary process theory, demonstrating fractionation of 3 autonomic and 9 ERP components to novelty, and disconfirming the unitary nature of the OR.     

Resting EEG theta power correlates with cognitive performance in healthy older adults

We address the degree to which resting EEG bandpower is associated with cognitive performance in 73 healthy older adults (aged 56-70). Relative theta (4-6.5 Hz) power was significantly correlated with immediate and delayed verbal recall, attention, and executive function measures. Relative delta and alpha power and peak alpha frequency did not correlate with any cognitive measures. These data indicate that high resting theta power in healthy older adults is associated with better cognitive function and may be a marker of healthy neurocognitive aging. Comparison of these with previous findings suggests that two forms of theta-frequency oscillations may exist; one indicative of healthy neurocognitive function and the other, EEG/alpha slowing linked to (future) substantial cognitive decline. Future EEG investigations of cognitive aging or decline should analyze both relative theta power and degree of EEG/alpha slowing so as not to confound these.     

Separating mismatch negativity (MMN) response from auditory obligatory brain responses in school‐aged children

Mismatch negativity (MMN) overlaps with other auditory event‐related potential (ERP) components. We examined the ERPs of 50 9‐ to 11‐year‐old children for vowels /i/, /y/ and equivalent complex tones. The goal was to separate MMN from obligatory ERP components using principal component analysis and equal probability control condition. In addition to the contrast of the deviant minus standard response, we employed the contrast of the deviant minus control response, to see whether the obligatory processing contributes to MMN in children. When looking for differences in speech deviant minus standard contrast, MMN starts around 112 ms. However, when both contrasts are examined, MMN emerges for speech at 160 ms whereas for nonspeech MMN is observed at 112 ms regardless of contrast. We argue that this discriminative response to speech stimuli at 112 ms is obligatory in nature rather than reflecting change detection processing.     

基于ERP情绪状态对工作记忆刷新功能影响研究

近年来,情绪对工作记忆的建设作用正逐步受到关注,尤其是情绪对工作记忆中央执行系统刷新功能的影响至关重要。组织16名青年受试者参与动态工作记忆任务实验,探讨积极、中性和消极三类不同情绪状态对工作记忆刷新功能的影响。实验首先采用国际情绪图片系统(IAPS)使受试者分别进入三类情绪状态,随后执行4个数字的动态工作记忆任务。结果发现,积极情绪状态下工作记忆刷新时间显著增长(积极情绪状态:(1.016±0.338) s;中性情绪状态:(0.814±0.347) s, P<0.05);刷新ERP在额中央部N2幅值显著小于中性情绪;工作记忆刷新的后期(400～1 000 ms),在频带13～30 Hz处的能量降低显著低于中性情绪。消极情绪状态下工作记忆刷新时间与中性情绪无显著差异;工作记忆刷新的早期(0～400ms),在频带0～8Hz处的能量升高显著低于中性情绪。以上结果说明积极情绪对工作记忆刷新存在干扰作用,但未发现消极情绪对工作记忆刷新的显著影响。有关情绪状态影响工作记忆刷新机制的初步研究将为提高工作记忆刷新绩效提供实验依据。     

Cognitive control in the intertrial interval: Evidence from EEG alpha power

This study used electroencephalogram (EEG) power spectrum analyses to characterize neural activity during the intertrial interval, a period during which online cognitive adjustments in response to errors or conflict are thought to occur. EEG alpha power was quantified as an inverse index of cerebral activity during the period between each response and the next stimulus in a Stroop task. Alpha power was significantly reduced following error responses compared to correct responses, indicating greater cerebral activity following errors. Reduced alpha power was also observed following Stroop conflict trials compared to no‐conflict trials, suggesting that conflict engages processes of mental adjustment. Finally, hemispheric differences in alpha power during the intertrial interval supported the complementary roles of the left and right hemispheres in behavioral activation and inhibition.     

Positive emotion speeds up conflict processing: ERP responses in an auditory Simon task

Emotions signal the particular relevance of situations, threatening or rewarding, and influence perception and behaviour accordingly. Research to date has predominantly investigated the impact of negative emotional stimuli. However, rapid reactions to positive emotional stimuli are similarly adaptive. Here, we tested the influence of positive emotional stimuli on attentional control, which enables reacting to conflicting stimulation. We therefore presented positive emotional and neutral words in an auditory Simon task. Reaction times revealed faster resolution of conflict when target stimuli were positive compared to neutral words. Also, emotion modulated the first conflict-sensitive event-related brain potential, a negativity at 420 ms, indicating an influence on early stages of conflict processing. These results complement recent data on negative stimuli and suggest that positive stimuli are equally salient. The rapid impact on attentional control is evolutionary highly adaptive as it reduces the time that conflict yields an organism incapable of responding to reward-signalling stimuli.     

Selective suppression of self-initiated sounds in an auditory stream: An ERP study

Numerous studies have shown that the N1 event-related potential (ERP) response is attenuated when it is elicited by self-initiated sounds. This N1 suppression effect is generally interpreted to reflect an internal prediction mechanism, which enables the discrimination of the sensory consequences of our own actions and those of others. The blocked design used in the forerunner studies (i.e., self- and externally initiated sounds presented in different blocks) seriously limits the relevance of these findings, because the N1 effect can simply be explained by contextual task differences. In the present study, self- and externally initiated sounds were mixed within blocks. N1 suppression was found, and its magnitude was even larger than that observed in a traditional blocked condition. This result supports the involvement of an internal prediction mechanism in the discrimination of the sensory consequences of one's own actions and those of others.     

Linking components of event-related potentials and autonomic measures of the orienting reflex

This study examined autonomic measures and event-related potentials (ERPs) associated with elicitation and habituation of the basic Orienting Reflex (OR). Subjects received 16 innocuous tones with intensity alternating between 60 and 80 dB, at long inter-stimulus intervals. There was no stimulus-related task, so we could examine the effects of stimulus novelty and intensity in the absence of task demands. Cardiac, respiratory, peripheral vasoconstriction, and electrodermal measures were recorded, as well as continuous EEG. Single-trial ERPs were obtained, and components extracted by Principal Components Analysis were examined for potential response fractionation in the central indices of stimulus processing. The predicted fractionation of autonomic measures was obtained: cardiac deceleration showed no systematic change with intensity or trials, respiratory pause showed a substantial main effect of trials but no intensity effects, peripheral vasoconstriction showed intensity but no trials effects, and electrodermal responses showed substantial main effects of trials and intensity. A range of intensity and novelty effects were obtained in components identified as the N1, P3a, P3b, Novelty P3, and the classic Slow Wave. The different stimulus–response profiles of the ERP components are discussed in relation to the autonomic response profiles within the context of a sequential processing theory of OR elicitation.     

基于被动听觉ERP范式的慢性意识障碍患者个体评估研究

近年来,大脑功能检测技术逐渐应用于意识障碍(DoC)患者的意识水平评估,以期降低仅依靠临床主观行为量表评估的误诊率。其中,被动听觉事件相关电位(ERPs)范式下诱发的N1和失匹配负波(MMN)成分被认为是反应DoC患者意识水平的关键脑功能指标,但目前仍局限于组别层面的统计分析结果,其在DoC患者个体水平的评估效能尚待挖掘。根据N1和MMN成分的特性,提出了一种适用于被动听觉ERPs范式下DoC患者个体评估的深度学习算法。该方法引入了特征融合的数据扩增策略,即在单被试数据中随机抽取不同类型的试次进行空间级联形成新的融合样本,并结合EEGNET深度学习算法实现自动化特征提取和分类识别。在包含132名被试的单试次数据集上进行测试。对健康被试(38名),微意识状态(40名)和植物状态(54名)患者进行三分类评估。统计分析结果表明,该样本融合策略可显著提升模型分类表现,并在单被试融合样本数量扩增至1 000时模型取得样本水平75.14%的平均分类准确率,以及被试水平83.00%的平均分类准确率,83.79%的精确率和84.02%的召回率。所提出的深度学习框架可有效克服传统方法中存在的个体评估能力不强的问题,为DoC患者个体评估提供新的研究思路。     

The P3 cognitive ERP has at least some sensory modality‐specific generators: Evidence from high‐resolution EEG

The P3 can arguably be named the most intensely studied ERP. In spite of more than 40 years of research, fundamental questions regarding the nature of its neural generators remain unresolved. While most studies conclude that the P3 is a true classical “endogenous” potential, and that its surface potential distribution remains constant across sensory modalities, these results are largely based on low‐density EEG recordings, without the use of high‐resolution methods such as the spherical spline Laplacian (SSL). Seventeen healthy participants performed a three‐stimulus oddball task in visual and auditory modality while their EEG was recorded using a 128‐channel system. Comparison of amplitude‐normalized SSL estimated P3 brain‐surface potentials, and analysis of spatial and temporal correlations revealed significant differences between visual and auditory evoked P3 topographies from target and distractor stimuli (but not target minus frequent or distractor minus frequent comparisons). Based on these results, we postulate the likely existence of at least some sensory modality‐specific neuronal generators of the P3.     

EEG-correlates of trait anxiety in the stop-signal paradigm

The relationship between trait anxiety and event-related EEG oscillatory reactions in the stop-signal paradigm was studied in 15 non-clinical subjects with average age of 26 years (13 men). In the paradigm, subjects responded to target stimuli by pressing one of the two choice buttons. In 30 out of 130 trials, target presentation was followed by a stop-signal, indicating that subjects had to refrain from a prepared motor response. The subject's level of anxiety was assessed using the State Trait Anxiety Inventory. Wide-band desynchronization (8-25 Hz) was found before button-press. It was sustained after the subjects pressed the button at 7-14 Hz frequency range. Also, synchronization at 15-25 Hz band occurred in 400-1400 ms after the button-press. Synchronization at lower frequencies (1-7 Hz) was also found during 0-700 ms after the stop-signal onset. Also, desynchronization at 8-20 Hz was found in 300-800 ms after stop-signal onset. The group with higher anxiety showed desynchronization at 10-13 Hz in 0-800 ms after the button-press, whereas the group with lower anxiety showed synchronization at the same frequency range. In 0-600 ms after stop-signal onset, desynchronization at 8-13 Hz was observed in the group with higher anxiety, whereas the group with lower anxiety demonstrated synchronization or weak desynchronization. Our findings support the Eysenck et al. [M.W. Eysenck, N. Derakshan, R. Santos, M.G. Calvo, Anxiety and cognitive performance: attentional control theory, Emotion 7(2) (2007) 336-356] theory that subjects with higher anxiety have more attentional control over reaction and increased use of processing resources as compared with lower anxiety subjects.