The neural substrate for dreaming: is it a subsystem of the default network?

Building on the content, developmental, and neurological evidence that there are numerous parallels between waking cognition and dreaming, this article argues that the likely neural substrate that supports dreaming, which was discovered through converging lesion and neuroimaging studies, may be a subsystem of the waking default network, which is active during mind wandering, daydreaming, and simulation. Support for this hypothesis would strengthen the case for a more general neurocognitive theory of dreaming that starts with established findings and concepts derived from studies of waking cognition and neurocognition. If this theory is correct, then dreaming may be the quintessential cognitive simulation because it is often highly complex, often includes a vivid sensory environment, unfolds over a duration of a few minutes to a half hour, and is usually experienced as real while it is happening.     

Neural correlates of temporality: default mode variability and temporal awareness

The continual background awareness of duration is an essential structure of consciousness, conferring temporal extension to the many objects of awareness within the evanescent sensory present. Seeking the possible neural correlates of ubiquitous temporal awareness, this article reexamines fMRI data from off-task "default mode" (DM) periods in 25 healthy subjects studied by Grady et al. ("Age-related Changes in Brain Activity across the Adult Lifespan,"Journal of Cognitive Neuroscience 18(2), 2005). "Brain reading" using support vector machines detected information specifying elapsed time, and further analysis specified distributed networks encoding implicit time. These networks fluctuate; none are continuously active during DM. However, the aggregate regions of greatest variability closely resemble the default mode network. It appears that the default mode network has an important role as a state-dependent monitor of temporality.     

基于Think/No-think范式的动机性遗忘研究:行为与脑机制

想/不想范式(Think/No-think,TNT)是基于go/no-go范式提出来的用于研究动机性遗忘过程的实验范式,主要过程是指个体对于记忆的提取抑制可以导致随后该记忆的遗忘。近年来TNT范式的大量行为学研究都一致性地发现记忆提取抑制可以产生负性控制效应,验证了在实验室情境下对动机性遗忘进行研究的可行性。其中,负性控制效应指的是压抑条件的项目相对于基线条件的项目的回忆量有显著降低。关于动机性遗忘发生的神经机制的探讨已积累了大量的研究证据,总结脑电(EEG)和功能核磁共振(f MRI)两个模态的研究,我们提出了动机性遗忘发生的多模态功能网络模型。最后,在该模型的基础上,我们展望了TNT范式未来的研究方向,其中特别注意到同步EEG-f MRI技术的应用有望为我们揭示出记忆提取抑制导致的动机性遗忘发生的动态过程。     

Phenomenal consciousness in dreams and in mind wandering

Dreaming can be explained as the product of an interaction among memory processes, elaborative processes, and phenomenal awareness. A feedback circuit is activated by this interaction according to the associative links and the requirements of the dream scene. Recently, it has been hypothesized that a partial similarity exists between dreaming and mind wandering and that these two processes may involve the same neural default network. This commentary discusses the differences and similarities between phenomenal consciousness during dreaming and phenomenal consciousness during mind wandering from the perspective of the “continuity” of engagement of cognitive systems. The greatest difference consists in the lack of reality testing during dreaming. Dream imagery is hallucinatory by nature. Consequently, the simulated world in dreams makes dream imagery more akin to perception. In contrast, the imagery of mind wandering is more similar to imagination. The level of meta-awareness is preserved more frequently and to a greater degree in mind wandering.     

Electrophysiological correlates of dispositional mindfulness: A quantitative and complexity EEG study

While growing evidence supports that dispositional mindfulness relates to psychological health and cognitive enhancement, to date there have been only a few attempts to characterize its neural underpinnings. In the present study, we aimed at exploring the electrophysiological (EEG) signature of dispositional mindfulness using quantitative and complexity measures of EEG during resting state and while performing a learning task. Hundred twenty participants were assessed with the Five Facet Mindfulness Questionnaire and underwent 5 min eyes-closed resting state and 5 min at task EEG recording. We hypothesized that high mindfulness individuals would show patterns of brain activity related to (a) lower involvement of the default mode network (DMN) at rest (reduced frontal gamma power) and (b) a state of ‘task readiness’ reflected in a more similar pattern from rest to task (reduced overall q-EEG power at rest but not at task), as compared to their low mindfulness counterparts. Dispositional mindfulness was significantly linked to reduced frontal gamma power at rest and lower overall power during rest but not at task. In addition, we found a trend towards higher entropy during task performance in mindful individuals, which has recently been reported during mindfulness meditation. Altogether, our results add to those from expert meditators to show that high (dispositional) mindfulness seems to have a specific electrophysiological pattern characteristic of less involvement of the DMN and mind-wandering processes.     

The dynamics of affect across the wake-sleep cycle: From waking mind-wandering to night-time dreaming

Affective experiences occur across the wake-sleep cycle—from active wakefulness to resting wakefulness (i.e., mind-wandering) to sleep (i.e., dreaming). Yet, we know little about the dynamics of affect across these states. We compared the affective ratings of waking, mind-wandering, and dream episodes. Results showed that mind-wandering was more positively valenced than dreaming, and that both mind-wandering and dreaming were more negatively valenced than active wakefulness. We also compared participants’ self-ratings of affect with external ratings of affect (i.e., analysis of affect in verbal reports). With self-ratings all episodes were predominated by positive affect. However, the affective valence of reports changed from positively valenced waking reports to affectively balanced mind-wandering reports to negatively valenced dream reports. These findings show that (1) the positivity bias characteristic to waking experiences decreases across the wake-sleep continuum, and (2) conclusions regarding affective experiences depend on whether self-ratings or verbal reports describing these experiences are analysed.     

The precuneus and consciousness

This article reviews the rapidly growing literature on the functional anatomy and behavioral correlates of the precuneus, with special reference to imaging neuroscience studies using hamodynamic techniques. The precuneus, along with adjacent areas within the posteromedial parietal cortex, is among the most active cortical regions according to the "default mode" of brain function during the conscious resting state, whereas it selectively deactivates in a number of pathophysiological conditions (ie, sleep, vegetative state, drug-induced anesthesia), and neuropsychiatric disorders (ie, epilepsy, Alzheimer's disease, and schizophrenia) characterized by impaired consciousness. These findings, along with the widespread connectivity pattern, suggest that the precuneus may play a central role in the neural network correlates of consciousness. Specifically, its activity seems to correlate with self-reflection processes, possibly involving mental imagery and episodic/autobiographical memory retrieval.     

When we like what we know – A parametric fMRI analysis of beauty and familiarity

This paper presents a neuroscientific study of aesthetic judgments on written texts. In an fMRI experiment participants read a number of proverbs without explicitly evaluating them. In a post-scan rating they rated each item for familiarity and beauty. These individual ratings were correlated with the functional data to investigate the neural correlates of implicit aesthetic judgments. We identified clusters in which BOLD activity was correlated with individual post-scan beauty ratings. This indicates that some spontaneous aesthetic evaluation takes place during reading, even if not required by the task. Positive correlations were found in the ventral striatum and in medial prefrontal cortex, likely reflecting the rewarding nature of sentences that are aesthetically pleasing. On the contrary, negative correlations were observed in the classic left frontotemporal reading network. Midline structures and bilateral temporo-parietal regions correlated positively with familiarity, suggesting a shift from the task-network towards the default network with increasing familiarity.     

Functional Brain Connectivity Using fMRI in Aging and Alzheimer’s Disease

Normal aging and Alzheimer’s disease (AD) cause profound changes in the brain’s structure and function. AD in particular is accompanied by widespread cortical neuronal loss, and loss of connections between brain systems. This degeneration of neural pathways disrupts the functional coherence of brain activation. Recent innovations in brain imaging have detected characteristic disruptions in functional networks. Here we review studies examining changes in functional connectivity, measured through fMRI (functional magnetic resonance imaging), starting with healthy aging and then Alzheimer’s disease. We cover studies that employ the three primary methods to analyze functional connectivity—seed-based, ICA (independent components analysis), and graph theory. At the end we include a brief discussion of other methodologies, such as EEG (electroencephalography), MEG (magnetoencephalography), and PET (positron emission tomography). We also describe multi-modal studies that combine rsfMRI (resting state fMRI) with PET imaging, as well as studies examining the effects of medications. Overall, connectivity and network integrity appear to decrease in healthy aging, but this decrease is accelerated in AD, with specific systems hit hardest, such as the default mode network (DMN). Functional connectivity is a relatively new topic of research, but it holds great promise in revealing how brain network dynamics change across the lifespan and in disease.     

创造性思维四阶段的神经基础

华莱士(Wallas)四阶段论是创造性思维过程研究的重要模型, 该模型认为创造性思维包括准备期、酝酿期、明朗期、验证期。相关神经机制研究表明, 准备期主要包括题目呈现前大脑状态和静息状态的研究, 内侧额叶/ACC及颞叶构成准备期网络; 酝酿期主要包括酝酿期提示、延迟顿悟以及心智游移的相关研究, 这一阶段涉及左右脑的共同参与, 海马、腹内侧前额叶等脑区在酝酿过程中起重要作用; 现有顿悟研究反映明朗期和验证期神经活动, 前额叶、扣带回、颞上回、海马、楔叶、楔前叶、舌回、小脑等在内的脑区构成其神经基础, 其中, 扣带回、前额叶在不同角度进行的研究中均有参与, 颞上回是负责远距离联想的关键脑区, 海马参与定势打破与新颖联系形成, 外侧额叶是定势转移的关键脑区, 楔前叶、左侧额下/额中回、舌回在原型激活中起关键作用, 左外侧前额叶参与对答案细节性的验证加工。未来研究可从研究对象、研究内容、研究手段三方面加以改进, 以对创造性思维过程作更系统的探讨。     

EEG asymmetry and sleep mentation during REM and NREM

The hypothesis that dreaming is mediated by the right hemisphere was evaluated by monitoring EEG power asymmetry during REM and NREM sleep, and obtaining mentation reports when short-term temporal shifts in the EEG indicated relative left- or right-hemispheric dominance. Content analyses provided no support for the right-hemisphere hypothesis; indeed, some scales showed higher content during relative left-hemispheric dominance. In contrast to earlier reports, no difference between REM and NREM in EEG asymmetry was observed.     

EEG and fMRI agree: Mental arithmetic is the easiest form of imagery to detect

fMRI and EEG during mental imagery provide alternative methods of detecting awareness in patients with disorders of consciousness (DOC) without reliance on behaviour. Because using fMRI in patients with DOC is difficult, studies increasingly employ EEG. However, there has been no verification that these modalities provide converging information at the individual subject level. The present study examined simultaneous EEG and fMRI in healthy volunteers during six mental imagery tasks to determine whether one mental imagery task generates more robust activation across subjects; whether activation can be predicted from familiarity with the imagined activity; and whether EEG and fMRI converge upon the same conclusions about individual imagery performance. Mental arithmetic generated the most robust activation in the majority of subjects for both EEG and fMRI, and level of activation could not be predicted from familiarity, with either modality. We conclude that overall, EEG and fMRI agree regarding individual mental imagery performance.     

Self-reflection and the temporal focus of the wandering mind

Current accounts suggest that self-referential thought serves a pivotal function in the human ability to simulate the future during mind-wandering. Using experience sampling, this hypothesis was tested in two studies that explored the extent to which self-reflection impacts both retrospection and prospection during mind-wandering. Study 1 demonstrated that a brief period of self-reflection yielded a prospective bias during mind-wandering such that participants’ engaged more frequently in spontaneous future than past thought. In Study 2, individual differences in the strength of self-referential thought — as indexed by the memorial advantage for self rather than other-encoded items — was shown to vary with future thinking during mind-wandering. Together these results confirm that self-reflection is a core component of future thinking during mind-wandering and provide novel evidence that a key function of the autobiographical memory system may be to mentally simulate events in the future.     

创造性思维的脑机制

创造性思维是创造性的核心。近年来,脑电和脑成像技术的发展为研究创造性思维的神经基础提供了有力的技术支持,对创造性思维的脑机制研究取得了较大进展。创造性思维的脑机制研究主要包括顿悟的脑机制、发散性思维的脑机制、远距离联想的脑机制、言语创造性和图画创造性的对比的脑机制研究。研究结果显示创造性思维需要多个脑区的参与,因不同的认知任务其关键脑区而有所不同。对创造性思维的脑机制研究进行了总结,对这些研究可能存在创造性思维究竟应该定义为“领域一般的”还是“领域特殊的”的解释进行了讨论,并指出了研究中可能存在的基线任务设置问题和未来研究中需要在研究手段、研究设计、研究领域等方面加以改进的建议     

眼动与脑电同步记录技术在心理语言学研究中的新进展

传统的心理语言学研究手段存在一定的弊端,眼动和脑电同步记录技术具有高时间和高空间分辨率的特性,能够在自然阅读情境下探讨人在阅读中认知加工的时间进程及其相应的神经机制。本文在阐述眼动与脑电同步记录的必要性和方法的基础上,较为全面地介绍了近10年来同步记录技术在心理语言学研究中的新进展,并对该技术的应用前景进行了展望,以期对国内从事心理语言学领域的研究者有一定的启示。     

Cognitive control in belief‐laden reasoning during conclusion processing: An ERP study

Belief bias is the tendency to accept conclusions that are compatible with existing beliefs more frequently than those that contradict beliefs. It is one of the most replicated behavioral findings in the reasoning literature. Recently, neuroimaging studies using functional magnetic resonance imaging (fMRI) and event‐related potentials (ERPs) have provided a new perspective and have demonstrated neural correlates of belief bias that have been viewed as supportive of dual‐process theories of belief bias. However, fMRI studies have tended to focus on conclusion processing, while ERPs studies have been concerned with the processing of premises. In the present research, the electrophysiological correlates of cognitive control were studied among 12 subjects using high‐density ERPs. The analysis was focused on the conclusion presentation phase and was limited to normatively sanctioned responses to valid–believable and valid–unbelievable problems. Results showed that when participants gave normatively sanctioned responses to problems where belief and logic conflicted, a more positive ERP deflection was elicited than for normatively sanctioned responses to nonconflict problems. This was observed from ?400 to ?200 ms prior to the correct response being given. The positive component is argued to be analogous to the late positive component (LPC) involved in cognitive control processes. This is consistent with the inhibition of empirically anomalous information when conclusions are unbelievable. These data are important in elucidating the neural correlates of belief bias by providing evidence for electrophysiological correlates of conflict resolution during conclusion processing. Moreover, they are supportive of dual‐process theories of belief bias that propose conflict detection and resolution processes as central to the explanation of belief bias.     

Neural correlates of rumination in adolescents with remitted major depressive disorder and healthy controls

The aim of the present study was to use fMRI to examine the neural correlates of engaging in rumination among a sample of remitted depressed adolescents, a population at high risk for future depressive relapse. A rumination induction task was used to assess differences in the patterns of neural activation during rumination versus a distraction condition among 26 adolescents in remission from major depressive disorder (rMDD) and in 15 healthy control adolescents. Self-report depression and rumination, as well as clinician-rated depression, were also assessed among all participants. All of the participants recruited regions in the default mode network (DMN), including the posterior cingulate cortex, medial prefrontal cortex, inferior parietal lobe, and medial temporal gyrus, during rumination. Increased activation in these regions during rumination was correlated with increased self-report rumination and symptoms of depression across all participants. Adolescents with rMDD also exhibited greater activation in regions involved in visual, somatosensory, and emotion processing than did healthy peers. The present findings suggest that during ruminative thought, adolescents with rMDD are characterized by increased recruitment of regions within the DMN and in areas involved in visual, somatosensory, and emotion processing.     

A critical review of ERP and fMRI evidence on L2 syntactic processing

The current review focuses on recent event-related brain potential (ERPs) and functional magnetic resonance imaging (fMRI) in L2 syntactic processing data. To this end, critical factors influencing both the dynamics of neural mechanisms (ERPs) and critical functional brain correlates (fMRI) are discussed. These entail the critical period hypothesis, levels of proficiency, cross-linguistic syntactic similarities and dissimilarities as well as brain bases that may or may not be shared during syntactic processing in a first (L1) and a second (L2) language. The data to date reveal that (i) the critical period hypothesis plays less of a significant role than initially discussed, (ii) L2 proficiency is a driving factor influencing peak and extent of activation in brain correlates and in neurophysiological mechanisms as a function of learning, and (iii) language transfer effects (i.e., positive transfer effects when L1 and L2 are structurally similar or negative transfer effects when L1 and L2 are structurally dissimilar) primarily from the L1 to the L2 and potentially vice versa need to be critically considered in future research.     

The influence of action observation on action execution: Dissociating the contribution of action on perception,perception on action,and resolving conflict

For more than 15 years, motor interference paradigms have been used to investigate the influence of action observation on action execution. Most research on so-called automatic imitation has focused on variables that play a modulating role or investigated potential confounding factors. Interestingly, furthermore, a number of functional magnetic resonance imaging (fMRI) studies have tried to shed light on the functional mechanisms and neural correlates involved in imitation inhibition. However, these fMRI studies, presumably due to poor temporal resolution, have primarily focused on high-level processes and have neglected the potential role of low-level motor and perceptual processes. In the current EEG study, we therefore aimed to disentangle the influence of low-level perceptual and motoric mechanisms from high-level cognitive mechanisms. We focused on potential congruency differences in the visual N190 ? a component related to the processing of biological motion, the Readiness Potential ? a component related to motor preparation, and the high-level P3 component. Interestingly, we detected congruency effects in each of these components, suggesting that the interference effect in an automatic imitation paradigm is not only related to high-level processes such as self-other distinction but also to more low-level influences of perception on action and action on perception. Moreover, we documented relationships of the neural effects with (autistic) behavior.     

Cognitive and emotional processes during dreaming: a neuroimaging view

Dream is a state of consciousness characterized by internally-generated sensory, cognitive and emotional experiences occurring during sleep. Dream reports tend to be particularly abundant, with complex, emotional, and perceptually vivid experiences after awakenings from rapid eye movement (REM) sleep. This is why our current knowledge of the cerebral correlates of dreaming, mainly derives from studies of REM sleep. Neuroimaging results show that REM sleep is characterized by a specific pattern of regional brain activity. We demonstrate that this heterogeneous distribution of brain activity during sleep explains many typical features in dreams. Reciprocally, specific dream characteristics suggest the activation of selective brain regions during sleep. Such an integration of neuroimaging data of human sleep, mental imagery, and the content of dreams is critical for current models of dreaming; it also provides neurobiological support for an implication of sleep and dreaming in some important functions such as emotional regulation.