A novel single-trial event-related potential estimation method based on compressed sensing

Cognitive functions are often studied using eventrelated potentials（ERPs）that are usually estimated by an averaging algorithm.Clearly,estimation of single-trial ERPs can provide researchers with many more details of cognitive activity than the averaging algorithm.A novel method to estimate single-trial ERPs is proposed in this paper.This method includes two key ideas.First,singular value decomposition was used to construct a matrix,which mapped singletrial electroencephalographic recordings（EEG）into a low-dimensional vector that contained little information from the spontaneous EEG.Second,we used the theory of compressed sensing to build a procedure to restore single-trial ERPs from this low-dimensional vector.ERPs are sparse or approximately sparse in the frequency domain.This fact allowed us to use the theory of compressed sensing.We verified this method in simulated and real data.Our method and dVCA（differentially variable component analysis）,another method of single-trial ERPs estimation,were both used to estimate single-trial ERPs from the same simulated data.Results demonstrated that our method significantly outperforms dVCA under various conditions of signal-to-noise ratio.Moreover,the single-trial ERPs estimated from the real data by our method are statistically consistent with the theories of cognitive science.     

负性情绪刺激的反应启动效应事件相关电位的实验研究

目的：许多研究观察到，有机体对负性情绪刺激的反应比对中性或正性刺激快，本研究应用事件相关电位中的单侧化准备电位将反应时划分为刺激加工阶段和反应准备阶段，从而得以直接观察负性刺激的反应启动效应。方法：本研究选取国际情感图片系统的正、中、负性图片作为剌激材料，以正常大学生为被试，令其按键表示对图片情绪属性的判断，同时记录脑电。结果：正、负性情绪刺激引起的刺激锁定单侧化准备电位的潜伏期比中性条件下的潜伏期缩短，观察反应锁定单侧化准备电位的潜伏期可见，负性刺激引起的潜伏期显著短于中性和正性条件。结论：对情绪性刺激的心理加工评价过程较短，观察反应锁定单侧化准备电位的潜伏期可见，负性剌激引起的潜伏期显著短于中性和正性条件，表明负性刺激具有反应启动效应.     

Timing the fearful brain: unspecific hypervigilance and spatial attention in early visual perception

Numerous studies suggest that anxious individuals are more hypervigilant to threat in their environment than nonanxious individuals. In the present event-related potential (ERP) study, we sought to investigate the extent to which afferent cortical processes, as indexed by the earliest visual component C1, are biased in observers high in fear of specific objects. In a visual search paradigm, ERPs were measured while spider-fearful participants and controls searched for discrepant objects (e.g. spiders, butterflies, flowers) in visual arrays. Results showed enhanced C1 amplitudes in response to spatially directed target stimuli in spider-fearful participants only. Furthermore, enhanced C1 amplitudes were observed in response to all discrepant targets and distractors in spider-fearful compared with non-anxious participants, irrespective of fearful and non-fearful target contents. This pattern of results is in line with theoretical notions of heightened sensory sensitivity (hypervigilance) to external stimuli in high-fearful individuals. Specifically, the findings suggest that fear facilitates afferent cortical processing in the human visual cortex in a non-specific and temporally sustained fashion, when observers search for potential threat cues.     

Setbacks,pleasant surprises and the simply unexpected: brainwave responses in a language comprehension task

This event-related potential (ERP) study explored the behaviour of N400 and post-N400 frontal positivities (pN400FP) during the processing of emotionally biased and unbiased sentences that randomly led to highly expected or unexpected word outcomes. Unexpected outcomes (as determined by sentence completion written tests) elicited significantly larger N400 and pN400FP responses than did highly expected outcomes. Emotionally neutral outcomes triggered a significant N400 expectancy effect across all scalp locations, including frontal sites, whereas emotionally biased outcomes elicited a significant N400 effect localized to posterior scalp regions. The subsequent pN400FP effect was significant only when emotional expectations were violated and not when emotionally neutral sentences led to unexpected outcomes. This frontal effect, linked to the processing of lexically unexpected but plausible words, showed larger amplitudes for unexpected pleasant surprises than for unexpected setbacks. Our results support the view that the pN400FP response to unexpected verbal outcomes entails more than a generic reaction to a lexical ‘misprediction’. Rather, they favour the hypothesis that the affective content of the sentence being processed influences the effort needed to override a lexical prediction, such that more effort is needed to override a pessimistic prediction than an optimistic one.     

Age- and performance-related differences in source memory retrieval during early childhood: Insights from event-related potentials

Across early childhood, children's ability to remember individual items and the details that accompany these items (i.e., episodic memory) improves greatly. Given that these behavioral improvements coincide with increases in age, effects of age and performance are often confounded. This study used event-related potentials (ERPs) to investigate age- and performance-related differences in the neural processes underlying the development of memory for details during early childhood. Using a source memory paradigm, ERP components related to episodic memory, the negative component (Nc), and late slow wave (LSW) were examined in 4- to 8-year-old children. Analyses focused on trials for which children correctly remembered the source related to an item versus trials where the item was remembered but the source was forgotten. Results revealed LSW, but not Nc, differed as a function of age and performance. Specifically, LSW effects were similar across source correct and source incorrect trials in all high-performing children and in low-performing older children; however, LSW effects differed across conditions in low-performing younger children. Results show developmental differences in retrieval processes across early childhood and highlight the importance of considering age and performance when examining electrophysiological correlates of episodic memory during development.     

Electrocortical measures of performance monitoring from go/no-go and flanker tasks: Differential relations with trait dimensions of the triarchic model of psychopathy

This study examined associations of performance-monitoring event-related potentials (ERPs) from go/no-go and flanker tasks with one another, and with psychopathy-related traits of disinhibition, meanness, and boldness. A task-dependent relationship was evident between the error-related negativity (ERN) and trait disinhibition, with high-disinhibited participants showing reduced no-go ERN but not flanker ERN. Disinhibition was also inversely related to variants of the P3 and the error positivity (Pe) from these two tasks. A factor analysis of the ERPs revealed two distinct factors, one reflecting shared variance among the P3 and Pe measures from the two tasks, and the other covariance among the N2 and ERN measures. Scores on the P3/Pe factor, but not the N2/ERN factor, were inversely related to disinhibition, and accounted for associations of this trait with variants of the P3 and Pe across tasks. The implication is that high trait disinhibition relates mainly to reductions in brain responses associated with later elaborative stages in the processing of motivationally significant events across different tasks. Importantly, no-go ERN predicted disinhibition scores beyond N2/ERN factor scores, indicating that high disinhibition is not generally related to diminished early preresponse conflict and error processing, but rather to processing impairments in conditions calling for inhibition of prepotent response tendencies.     

Attention bias in earthquake-exposed survivors: An event-related potential study

The Chinese Wenchuan earthquake, which happened on the 28th of May in 2008, may leave deep invisible scars in individuals. China has a large number of children and adolescents, who tend to be most vulnerable because they are in an early stage of human development and possible post-traumatic psychological distress may have a life-long consequence. Trauma survivors without post-traumatic stress disorder (PTSD) have received little attention in previous studies, especially in event-related potential (ERP) studies. We compared the attention bias to threat stimuli between the earthquake-exposed group and the control group in a masked version of the dot probe task. The target probe presented at the same space location consistent with earthquake-related words was the congruent trial, while in the space location of neutral words was the incongruent trial. Thirteen earthquake-exposed middle school students without PTSD and 13 matched controls were included in this investigation. The earthquake-exposed group showed significantly faster RTs to congruent trials than to incongruent trials. The earthquake-exposed group produced significantly shorter C1 and P1 latencies and larger C1, P1 and P2 amplitudes than the control group. In particular, enhanced P1 amplitude to threat stimuli was observed in the earthquake-exposed group. These findings are in agreement with the prediction that earthquake-exposed survivors have an attention bias to threat stimuli. The traumatic event had a much greater effect on earthquake-exposed survivors even if they showed no PTSD symptoms than individuals in the controls. These results will provide neurobiological evidences for effective intervention and prevention to post-traumatic mental problems.     

Smoking motivation in normal subjects using event-related potentials

The goal of the present study was to evaluate the effects of acute nicotine administration following 18 h of abstinence from cigarette smoking. Event-related potentials (ERPs) were measured in 13 male volunteers for five successive sessions. The peak amplitude and the area of the P300 significantly increased during acute withdrawal. An increase in P300 values also was observed following resumption of smoking. However, in subjects pretreated with nicotine gum, no increase in P300 values was observed following resumption of smoking. The increase in P300 values persisted for several weeks and returned to control values following 1 month of routine daily smoking. The P300 amplitude was negatively correlated with the daily dose of nicotine. These results suggest that attention and/or arousal may be enhanced by the withdrawal and the resumption of smoking. The mechanisms involved in CNS hypersensitivity to motivate the subject to smoke may persist in the presence of an increased P300 value, even following resumption of routine daily smoking.     

Ammonia metabolism,the brain and fatigue; revisiting the link

This review addresses the ammonia fatigue theory in light of new evidence from exercise and disease studies and aims to provide a view of the role of ammonia during exercise. Hyperammonemia is a condition common to pathological liver disorders and intense or exhausting exercise. In pathology, hyperammonemia is linked to impairment of normal brain function and the onset of the neurological condition, hepatic encephalopathy. Elevated blood ammonia concentrations arise due to a diminished capacity for removal via the liver and lead to increased exposure of organs, such as the brain, to the toxic effects of ammonia. High levels of brain ammonia can lead to deleterious alterations in astrocyte morphology, cerebral energy metabolism and neurotransmission, which may in turn impact on the functioning of important signalling pathways within the neuron. Such changes are believed to contribute to the disturbances in neuropsychological function, in particular the learning, memory, and motor control deficits observed in animal models of liver disease and also patients with cirrhosis. Hyperammonemia in exercise occurs as a result of an increased production by contracting muscle, through adenosine monophosphate (AMP) deamination (the purine nucleotide cycle) and branched chain amino acid (BCAA) deamination prior to oxidation. Plasma concentrations of ammonia during exercise often achieve or exceed those measured in liver disease patients, resulting in increased cerebral uptake. In this article we propose that exercise-induced hyperammonemia may lead to concomitant disturbances in brain function, potentially through similar mechanisms underpinning pathology, which may impact on performance as fatigue or reduced function, especially during extreme exercise.     

利用事件相关电位探索三种听觉Oddball范式脑加工机制的研究

目的:开发一组新的听觉Oddball范式,通过事件相关电位观察其在健康受试者中的脑加工反应。方法:社会招募健康志愿者15名(男8名,女7名,平均年龄40±9岁),分别进行纯音-正名(TS),其他名字-正名(OS)和反名-正名(RS)三组难度依次增大的听觉Oddball范式的事件相关电位检查,分析比较各组MMN和P300潜伏期和波幅的差异。结果:三组实验范式在所有健康志愿者中均诱发得到失匹配负波(mismatch negativity,MMN)和P300,TS组MMN和P300的潜伏期最短,OS组次之,RS组最长(P0.05),但OS组和RS组统计学分析无显著性差异(P0.05);MMN的波幅TS组最大,OS组次之,RS组最小(P0.05),但OS组和RS组统计学分析无显著性差异(P0.05);各组之间P300波幅比较未发现显著性差异(P0.05)。结论:三组听觉Oddball实验范式有一定的区分难度,有望进一步应用于植物状态/无反应觉醒综合征患者和最小意识状态患者的鉴别诊断和预后预测。