刺激相关冲突与任务相关冲突在脑内的并行处理

目的 探讨大脑对刺激相关和任务相关冲突的处理机制。方法 受试分别默数数值相同和不同的数字对出现的次数并记录头皮事件相关电位。数字对分为４种情况:没有冲突、刺激相关冲突、任务相关冲突、刺激相关和任务相关双重冲突。结果 ３种冲突的数字对在第２个数字后引起事件相关电位Ｎ２７０，没有冲突的数字对则无该负波，Ｎ２７０的起始潜伏期终止时间在３种冲突之间没有显差异。结论 大脑并行处理刺激相关和任务相关冲突。     

人脑对外源性和内源性信息冲突处理机制的探讨

目的 采用事件相关电位技术研究人脑对外源性刺激相关的信息冲突和内源性心理相关的信息冲突的处理机制.方法 15名健康志愿者参与试验.视觉刺激为白色的两位数字,先后呈现的两个数字(S1和S2)组成一个刺激对.任务1要求受试者比较S1和S2的数值是否相同,并做出相应的按键反应.刺激对包含S1与S2的数值相同(S-)和S1与S2数值不同(S+)两种类型.任务2要求受试者心算S1与S2的差,并把计算结果与数字"3"做比较,对差等于"3"(M-)和不等于"3"(M+)的情况做出相应的按键反应.刺激对包含3种类型:S1与S2数值相同,差值不等于"3"(S-M+);数值不同但差等于"3"(S+M-);数值不同且差不等于"3"(S+M+).结果 S2呈现后,S+、S+M-和S-M+类型的刺激对均引出N270,S+M+则依次引出N270和N400两个成分.N270的最大波幅出现在后头部,N400的最大波幅则位于中央区.结论 N270和N400的出现提示人脑对外源性和内源性信息冲突的处理采用的是串行处理模式.该处理活动可能是由冲突处理系统中不同的神经结构来完成的.     

不同手反应对冲突监测事件相关电位N270的影响

目的：探讨不同手作业反应对冲突监测事件相关电位N270的影响。方法：要求受试判断前后呈现的两个刺激颜色是否相同，并做出按键反应，同步从头皮记录事件相关电位，在前一半实验中，受试用一只手的两个不同手指按键，在后一半实验中，受试用另一只手按键。结果：当两个刺激的颜色不同时，第2个刺激诱发出了N100、N160、N200、PLC和N270。N270主要分布在前头部额中央区。在第2个刺激之前的伴随性负变化（contingent negative variation,CNV)在受试用右手反应时波幅明显增高，但CNV的存在不影响N160、N200和N270的波幅。N160和N200在受试用左手按键反应时波幅明显增高。而N270的波幅在左右手反应之间无明显区域。结论：冲突监测事件相关电位N270的波幅不受不同手反应的影响。     

空间位置冲突信息诱发的事件相关电位

目的使用事件相关电位技术,探讨人脑处理空间位置信息冲突的工作机制。方法采用美国Neuroscan脑电诱发电位工作站,对16例健康受试者做刺激匹配的事件相关电位研究,要求受试者判断前后两个刺激的空间位置是否相同,并做出按键反应。结果当一对刺激的位置不同时,在第二个刺激出现后约270ms处从头皮可记录到一个明显的负波(N270),波幅以后头部最为明显。结论空间位置信息冲突可以诱发N270的产生。     

空间位置冲突信息诱发的事件相关电位

目的：使用事件相关电位技术，探讨人脑处理空间位置信息冲突的工作机制。方法：采用美国Neuroscan脑电诱发电位工作站，对16例健康受试做刺激匹配的事件相关电位研究，要求受试判断前后两个刺激的空间位置是否相同，并做出按键反应。结果：当一对刺激的位置不同时，在第二个刺激出现后约270ms处从头皮可记录到一个明显的负波（N270），波幅以后头部最为明显。结论：空间位置信息冲突可以诱发N270的产生。     

认知事件相关电位冲突负波-N270与脑认知活动的关系

大脑接受外界的刺激,与大脑工作记忆中的信息相互比较,当外界进入脑内的信息与脑内的内源性信息相互矛盾、不一致时,可以在头皮表面记录到一个负波,其潜伏期约为270ms,所以称这个事件相关电位成分为N270。该成分也可以由脑内的两个概念相互矛盾所引出,反映了大脑对冲突信息进行加工处理的过程。     

认知事件相关电位冲突负波-N270与脑认知活动的关系

大脑接受外界的刺激，与大脑工作记忆中的信息相互比较，当外界进入脑内的信息与脑内的内源性信息相互矛盾、不一致时，可以在头皮表面记录到一个负波，其潜伏期约为270ms，所以称这个事件相关电位成分为N270。该成分也可以由脑内的两个概念相互矛盾所引出，反映了大脑对冲突信息进行加工处理的过程。     

不同手反应对冲突监测事件相关电位N270的影响

目的:探讨不同手作业反应对冲突监测事件相关电位N270的影响。方法:要求受试者判断前后呈现的两个刺激颜色是否相同,并做出按键反应,同步从头皮记录事件相关电位。在前一半实验中,受试者用一只手的两个不同手指按键,在后一半实验中,受试者用另一只手按键。结果:当两个刺激的颜色相同时,第2个刺激诱发出了N100、N160、N200和LPC。当两个刺激的颜色不同时,第2个刺激诱发出了N100、N160、N200、LPC和N270。N270主要分布在前头部额中央区。在第2个刺激之前的伴随性负变化(contingentnegativevariation,CNV)在受试者用右手反应时波幅明显增高,但CNV的存在不影响N160、N200和N270的波幅。N160和N200在受试者用左手按键反应时波幅明显增高,而N270的波幅在左右手反应之间无明显区别。结论:冲突监测事件相关电位N270的波幅不受不同手反应的影响。     

方向信息冲突诱发的事件相关电位

waveamplitudeishuge.TheorientaproductionofN270.目的:使用事件相关电位技术,探讨人脑处理方向信息冲突的工作机制。方法:选择首都医科大学的在读本科生10名(6名男生,年龄21～24岁)作为健康受试者(经书面同意),进行人脑对方向冲突的反应的观察。成对的相同动物图片(S1和S2)在屏幕上依次呈现。S1和S2都向左时称为左-左状态(状态1),S1和S2都向右时称为右-右状态(状态2),以上两种状态均视为匹配状态;当S1方向向左而S2向右时称为左-右状态(状态3),反之称为右-左状态(状态4),后两种状态则视为冲突状态。受试者的任务是判断成对出现的S1和S2出现方向是否相同,无论S1方向向左还是向右。采用美国Neuroscan脑电诱发电位工作站在给出刺激的同时在头皮记录事件相关电位存储在硬盘,经离线式叠加处理后分别对各成分进行不同状态间平均电压的比较。结果:10名被试的实验数据全部纳入分析统计。①4种状态(左-左状态、右-右状态、左-右状态和右-左状态)的反应时依次为(577±161)ms、(581±173)ms、(586±100)ms和(594±103)ms,正确率均为99%,差异无显著性意义[F(1,9)=8.94,P>0.05];[F(1,9)=13.87,P>0.05]。②全部4种状态均记录到由S2诱发的P100、N170、N200和P300,冲突状态下电极广泛记录到N270,在前头部额中央区明显。③分别对4种状态下各成分的平均波幅进行双因素方差分析显示:各成分的平均波幅在两种匹配状态和两种冲突状态之间差异均无显著性意义;与匹配状态相比,冲突状态下顶枕部P100和右侧额部P300平均波幅显著增高,右侧顶部和颞部N270平均波幅明显高于左侧;P300的平均波幅在匹配状态下,左侧顶部较右侧顶部高,而在冲突状态下,左右侧顶部的平均波幅差异无显著性意义。结论:当一对刺激的方向不同时,在增强的P100(P1)后可记录到一个明显的负波-N270,波幅以前头部较大。方向信息冲突可以诱发N270的产生。     

方向信息冲突诱发的事件相关电位

目的：使用事件相关电位技术，探讨人脑处理方向信息冲突的工作机制。 方法：选择首都医科大学的在读本科生10名（6名男生，年龄21-24岁）作为健康受试者（经书面同意），进行人脑对方向冲突的反应的观察。成对的相同动物图片（S1和S2）在屏幕上依次呈现。S1和S2都向左时称为左一左状态（状态1），S和1S2都向右时称为右一右状态（状态2），以上两种状态均视为匹配状态；当S1方向向左而S2向右时称为左一右状态（状态3），反之称为右一左状态（状态4），后两种状态则视为冲突状态。受试者的任务是判断成对出现的S1和S2出现方向是否相同，无论S1方向向左还是向右。采用美国Neuroscan脑电诱发电位工作站在给出刺激的同时在头皮记录事件相关电位存储在硬盘，经离线式叠加处理后分别对各成分进行不同状态问平均电压的比较。 结果：10名被试的实验数据全部纳入分析统计。①4种状态（左-左状态、右-右状态、左-右状态和右-左状态）的反应时依次为（577&;#177;161）ms、（581&;#177;173）ms、（586&;#177;100）ms和（594&;#177;103）ms，正确率均为99％，差异无显著性意义[F（1.91）=8．94，P〉0．05]；[F（1.91=13．87，P〉0．051。②全部4种状态均记录到由S2诱发的P100、N170、N200和P300，冲突状态下电极广泛记录到N270，在前头部额中央区明显。③分别对4种状态下各成分的平均波幅进行双因素方差分析显示：各成分的平均波幅在两种匹配状态和两种冲突状态之间差异均无显著性意义；与匹配状态相比，冲突状态下顶枕部P100和右侧额部P300平均波幅显著增高，右侧顶部和颞部N270平均波幅明显高于左侧；P300的平均波幅在匹配状态下，左侧顶部较右侧顶部高，而在冲突状态下，左右侧顶部的平均波幅差异无显著性意义。结论：当一对刺激的方向不同时，在增强的P100（P1）后可记录到一个明显的负波-N270，波幅以前头部较大。方向信息冲突可以诱发N270的产生。     

Dissociating action inhibition, conflict monitoring and sensory mismatch into independent components of event related potentials in GO/NOGO task

The anterior N2 and P3 waves of event related potentials (ERPs) in the GO/NOGO paradigm in trials related to preparatory set violations in previous studies were inconsistently associated either with action inhibition or conflict monitoring operations. In the present study a paired stimulus GO/NOGO design was used in order to experimentally control the preparatory sets. Three variants of the same stimulus task manipulated sensory mismatch, action inhibition and conflict monitoring operations by varying stimulus-response associations. The anterior N2 and P3 waves were decomposed into components by means of independent component analysis (ICA). The ICA was performed on collection of 114 individual ERPs in the three experimental conditions. Three of the independent components were selectively affected by the task manipulations indicating association of these components with sensory mismatch, action inhibition and conflict monitoring operations. According to sLORETA the sensory mismatch component was generated in the left and right temporal areas, the action suppression component was generated in the supplementary motor cortex, and the conflict monitoring component was generated in the anterior cingulate cortex.     

Separate conflict-specific cognitive control mechanisms in the human brain

To ensure optimal task performance, the human brain detects and resolves conflict in information processing via a cognitive control system. However, it is not known whether conflict resolution relies on a single central resource of cognitive control, or on a collection of independent control mechanisms that deal with different types of conflict. In order to address this question, we assessed behavioral and blood-oxygen-level-dependent (BOLD) responses during the simultaneous detection and resolution of two sources of conflict in a modified color-naming Stroop task: conflict stemming from incompatibility between the task-relevant and an irrelevant stimulus feature (stimulus-based or Stroop conflict), and conflict stemming from incompatibility between an irrelevant stimulus feature and response features (response-based or Simon conflict). Results show that control mechanisms recruited by stimulus-based conflict resolve stimulus-based conflict, but do not affect the resolution of response-based conflict, and vice versa. The resolution of response-based conflict was distinguished by modulation of activity in premotor cortex, whereas resolution of stimulus-based conflict was distinguished by the modulation of activity in parietal cortex. These results suggest that the human brain flexibly adopts, and independently controls, conflict-specific resolution strategies, biasing motor programming to resolve response-based conflict, and biasing stimulus representations to resolve stimulus-based conflict. We propose a non-centralized, modular architecture of cognitive control, where separate control resources operate in parallel, and are recruited in a context-sensitive manner.     

Cognitive and brain consequences of conflict

Tasks involving conflict between stimulus dimensions have been shown to activate dorsal anterior cingulate and prefrontal areas. It has been proposed that the dorsal anterior cingulate is involved a domain general process of monitoring conflict, while prefrontal areas are involved in resolving conflict. We examine three tasks that all require people to respond based on one stimulus dimension while ignoring another conflicting dimension, but which vary in the source of conflict. One of the tasks uses language stimuli (Stroop effect) and two use nonlanguage spatial conflicts appropriate for children and nonhuman animals. In Experiment 1, 12 participants were studied with event-related functional magnetic resonance imaging (fMRI) while performing each of the three tasks. Reaction times for each of the three tasks were significantly longer in the incongruent condition compared with the congruent condition, demonstrating that each task elicits a conflict. By studying the same people in the same session, we test the hypothesis that conflict activates a similar brain network in the three tasks. Significant activations were found in the anterior cingulate and left prefrontal cortex for all three conflict tasks. Within these regions, the conflict component demonstrated evidence for significant common activation across the three tasks, although the peak activation point and spatial extent were not identical. Other areas demonstrated activation unique to each task. Experiments 2-4 provide behavioral evidence indicating considerable independence between conflict operations involved in the tasks. The behavioral and fMRI results taken together seem to argue against a single unified network for processing conflict, but instead support either distinct networks for each conflict task or a single network that monitors conflict with different sites used to resolve the conflict.     

Preparatory allocation of attention and adjustments in conflict processing

Attentional control involves the ability to allocate preparatory attention to improve subsequent stimulus processing and response selection. There is behavioral evidence to support the hypothesis that increased expectancy of stimulus and response conflict may decrease the subsequent experience of conflict during task performance. We used a cued flanker and event-related fMRI design to separate processes involved in preparation from those involved in resolving conflict and to identify the brain systems involved in these processes as well as the association between preparatory activity levels and activity related to subsequent conflict processing. Our results demonstrate that preparatory attentional allocation following a cue to the upcoming level of conflict is mediated by a network involving Dorsolateral Prefrontal Cortex (DLPFC) and the Intraparietal Sulcus (IPS). Informed preparation for conflict processing was associated with decreased Anterior Cingulate Cortex/pre-Supplementary Motor Area (ACC/pre-SMA) and IPS activity during the flanker target presentation, supporting their roles in conflict processing and visuospatial attention during the flanker task. Ventrolateral Prefrontal Cortex/Orbitofrontal Cortex (VLPFC/OFC) was active when specific strategic task rule and outcome information was available.     

Motor conflict in Stroop tasks: Direct evidence from single-trial electro-myography and electro-encephalography

Several brain imaging studies have assumed that response conflict is present in Stroop tasks. However, this has not been demonstrated directly. We examined the time-course of stimulus and response conflict resolution in a numerical Stroop task by combining single-trial electro-myography (EMG) and event-related brain potentials (ERP). EMG enabled the direct tracking of response conflict and the peak latency of the P300 ERP wave was used to index stimulus conflict. In correctly responded trials of the incongruent condition EMG detected robust incorrect response hand activation which appeared consistently in single trials. In 50–80% of the trials correct and incorrect response hand activation coincided temporally, while in 20–50% of the trials incorrect hand activation preceded correct hand activation. EMG data provides robust direct evidence for response conflict. However, congruency effects also appeared in the peak latency of the P300 wave which suggests that stimulus conflict also played a role in the Stroop paradigm. Findings are explained by the continuous flow model of information processing: Partially processed task-irrelevant stimulus information can result in stimulus conflict and can prepare incorrect response activity. A robust congruency effect appeared in the amplitude of incongruent vs. congruent ERPs between 330–400 ms, this effect may be related to the activity of the anterior cingulate cortex.     

Common and distinct neural substrates of attentional control in an integrated Simon and spatial Stroop task as assessed by event-related fMRI

The purpose of this experiment was to directly examine the neural mechanisms of attentional control involved in the Simon task as compared to a spatial Stroop task using event-related fMRI. The Simon effect typically refers to the interference people experience when there is a stimulus-response conflict. The Stroop effect refers to the interference people experience when two attributes of the same stimulus conflict with each other. Although previous imaging studies have compared the brain activation for each of these tasks performed separately, none had done so in an integrated task that incorporates both types of interference, as was done in the current experiment. Both tasks activated brain regions that serve as a source of attentional control (dorsolateral prefrontal cortex) and posterior regions that are sites of attentional control (the visual processing stream-middle occipital and inferior temporal cortices). In addition, there were also specific brain regions activated to a significantly greater degree by one task and/or only by a single task. The brain regions significantly more activated by the Simon task were those sensitive to detection of response conflict, response selection, and planning (anterior cingulate cortex, supplementary motor areas, and precuneus), and visuospatial-motor association areas. In contrast, the regions significantly more activated by the Stroop task were those involved in biasing the processing toward the task-relevant attribute (inferior parietal cortex). These findings suggest that the interference effects of these two tasks are caused by different types of conflict (stimulus-response conflict for the Simon effect and stimulus-stimulus conflict for the Stroop effect) but both invoke similar sources of top-down modulation.     

Task by stimulus interactions in brain responses during Chinese character processing

In the visual word recognition literature, it is well understood that various stimulus effects interact with behavioral task. For example, effects of word frequency are exaggerated and effects of spelling-to-sound regularity are reduced in the lexical decision task, relative to reading aloud. Neuroimaging studies of reading often examine effects of task and stimulus properties on brain activity independently, but potential interactions between task demands and stimulus effects have not been extensively explored. To address this issue, we conducted lexical decision and symbol detection tasks using stimuli that varied parametrically in their word-likeness, and tested for task by stimulus class interactions. Interactions were found throughout the reading system, such that stimulus selectivity was observed during the lexical decision task, but not during the symbol detection task. Further, the pattern of stimulus selectivity was directly related to task difficulty, so that the strongest brain activity was observed to the most word-like stimuli that required "no" responses, whereas brain activity to words, which elicit rapid and accurate "yes" responses were relatively weak. This is in line with models that argue for task-dependent specialization of brain regions, and contrasts with the notion of task-independent stimulus selectivity in the reading system.     

Anterior Cingulate Cortex, Conflict Monitoring, and Levels of Processing

It has been hypothesized that the anterior cingulate cortex (ACC) contributes to cognition by detecting conflicts that might occur during information processing, to signal the need to engage top-down attentional processes. The present study was designed to investigate which levels of processing are being monitored by the ACC for the presence of conflict. Event-related fMRI was used to measure the response of the ACC during an interference task in which distracting information could be congruent, conflicting at the level of stimulus identification, or conflicting at the response level. Although both types of conflict caused reaction time interference, the fMRI data showed that the ACC is responsive only to response conflict, even when controlling for reaction times. These results suggest a highly specific contribution of the ACC to executive functions, through the detection of conflicts occurring at later or response-related levels of processing.