睡眠剥夺中感觉运动皮层和视觉皮层神经活动及警觉水平的改变

在睡眠剥夺(sleep deprivation, SD)过程中,人类大脑的神经活动和警觉水平如何受到影响,尤其是感觉运动和视觉系统,目前仍是研究的热点。静息状态功能磁共振成像(resting state functional magnetic resonance imaging,rfMRI)作为一种反映人脑自发活动的非侵入式成像技术,在睡眠剥夺的研究中得到了广泛应用。本研究采用9次重复rfMRI和心理运动警觉任务(psychomotor vigilance task,PVT),以探索23名志愿者在整个36小时的睡眠剥夺过程中神经活动和警觉水平的变化。我们采用基于PVT的平均反应时间(mean reaction time, MRT)和失效率(lapses ratio, LR)评估警觉水平的变化。我们采用基于rfMRI的区域同质性(region homogeneity,ReHo)和低频波动幅度(amplitude of low frequency fluctuation,ALFF)评估大脑神经活动变化。结果表明,感觉运动网络(sensorimotor network, SMN)和视觉区域(visual network, VN)是受到睡眠剥夺影响最严重的区域。我们采用组独立成分分析(Group Independent component analysis, GICA)将视觉相关区域划分为视觉I区、视觉II区、视觉关联区,并从解剖自动标记(Anatomical automatic labeling,AAL)模板中提取运动感觉相关区域,包括中央前/中央后回、中央旁小叶和辅助运动区。我们发现,睡眠剥夺后16 - 30小时脑神经活动及警惕性下降。我们采用2×3重复测量方差分析,探讨睡眠压力、昼夜节律及其交互作用对感觉运动相关和视觉相关脑区神经活动的影响。我们观察到睡眠压力与交互作用对感觉运动相关区域和视觉相关区域有显著影响。我们采用皮尔逊相关系数评估警觉水平变化与感觉运动相关和视觉相关脑区神经活动变化的关系。睡眠剥夺期间所有感觉运动相关区域的神经活动变化与警觉变化均存在显著的相关关系。我们的研究结果证实,睡眠剥夺从第一天24：00开始改变SMN和VN的警戒水平和神经活动,睡眠压力和昼夜节律在睡眠剥夺期间调节SMN和VN的神经活动。此外,昼夜节律的效应受到睡眠压力的显著调节。感觉运动相关区域和视觉相关区域的增强导致他们远程连接的减弱,这可能是睡眠剥夺期间响应时间变慢的原因。     

fMRI在视觉研究中的应用和进展

视觉研究对于揭示大脑的奥秘有着极其重要的意义.功能性磁共振成像（functional magnetic resonance imaging,fMRI）用于研究人脑的功能结构,主要是基于静脉毛细血管内血氧浓度的变化.fMRI可以无损伤地在几毫米级的空间分辨率和少于1 s的时间分辨率上观察清醒状态下人脑的活动,因此自90年代以来fMRI已经成为研究人脑的重要方法.fMRI在视觉研究中的应用已经使人们对视觉系统的功能性组织有了更好的理解,并取得了很多成果.今后的研究方向是进一步探讨人脑的意识、注意、记忆等高级功能的神经机制.     

综述与专论：人类疼痛的神经网络表征

疼痛是一种不愉快的感觉和情感体验,其涉及到多级神经加工过程,神经活动模式十分复杂。非侵入性脑功能成像技术可以实现在全脑水平上解析人类疼痛的神经机制。其中,功能磁共振成像（functional magnetic resonance imaging,fMRI）技术因具有高空间分辨率的优势,使其在探索人类疼痛的神经机制研究中得到了广泛的应用。本文聚焦于人类疼痛的fMRI研究,首先概述了疼痛相关的脑响应研究发现,梳理了与疼痛加工相关的多个脑区功能活动变化。然而,调节单一脑区的功能难以影响疼痛体验,提示疼痛加工涉及多脑区之间的协同作用。由此,本文综述了参与疼痛加工的脑区之间交互现象,这些研究揭示了多条神经通路以串行或并行的方式构成了复杂的疼痛神经网络,进而处理与疼痛相关的感觉、情绪和认知信息。基于上述研究,近年来不断更迭发展的超高场强fMRI及脑脊同步成像技术,助力人类疼痛研究深入到核团和脊髓层面,拓展了疼痛神经网络的精细度和全面性。综上,本文提出了人类疼痛的神经网络表征,并以此为基础指导神经调控技术调节异常的神经网络表征,进而实现缓解疼痛症状的目标。最后,本文讨论了当前疼痛神经表征研究的局限性,并提出了探索疼痛特异性表征,对比实验诱发性疼痛和临床自发性疼痛,以及疼痛个体化表征的研究展望。     

Neural Coding with Graded Membrane Potential Changes and Spikes

The neural encoding of sensory stimuli is usually investigated for spike responses, although many neurons are known to convey information by graded membrane potential changes. We compare by model simulations how well different dynamical stimuli can be discriminated on the basis of spiking or graded responses. Although a continuously varying membrane potential contains more information than binary spike trains, we find situations where different stimuli can be better discriminated on the basis of spike responses than on the basis of graded responses. Spikes can be superior to graded membrane potential fluctuations if spikes sharpen the temporal structure of neuronal responses by amplifying fast transients of the membrane potential. Such fast membrane potential changes can be induced deterministically by the stimulus or can be due to membrane potential noise that is influenced in its statistical properties by the stimulus. The graded response mode is superior for discrimination between stimuli on a fine time scale.     

Neural overlap in processing music and speech

Neural overlap in processing music and speech, as measured by the co-activation of brain regions in neuroimaging studies, may suggest that parts of the neural circuitries established for language may have been recycled during evolution for musicality, or vice versa that musicality served as a springboard for language emergence. Such a perspective has important implications for several topics of general interest besides evolutionary origins. For instance, neural overlap is an important premise for the possibility of music training to influence language acquisition and literacy. However, neural overlap in processing music and speech does not entail sharing neural circuitries. Neural separability between music and speech may occur in overlapping brain regions. In this paper, we review the evidence and outline the issues faced in interpreting such neural data, and argue that converging evidence from several methodologies is needed before neural overlap is taken as evidence of sharing.     

智能神经假体：心理与技术问题

近年来,微系统技术、神经计算和生物系统等高新技术的发展,为新型植入式智能神经假体装置的发展、生产和应用提供了巨大的可能。其中一项特别引人关注的进展就是智能视觉假体。虽然通过中枢视觉系统到知觉域的机制还未完全了解,但视觉假体是通过电刺激视觉通路的不同部位来产生有用的视觉感受。许多年前,哲学和心理物理学研究都强调视觉感受可能是由不同的原因所引起。为了研制视觉假体,我们使用两张映射图来描述中枢视觉系统的功能是如何实现的。我们提出一种具有自学习功能且包括几个阶段的视网膜编码器（retina encoder,RE）。视网膜模块的RE模拟视网膜的功能并假定其实现了模式P1从物理域到神经域的映射操作M1。与此相对应的,中枢视觉系统模块则实现另一个映射操作M2,即M1在神经域的输出信号被转换到知觉域而产生视觉感受P2。在设定的迭代和基于感受的学习过程中,一名拥有正常视力的被试参与实验来提供由P1而产生P2的感性的相似性估计作为学习算法的输入,该算法反过来调整RE的参数矢量使得P2足够接近P1。更具体的说,全部RE时空滤波器可以借助遗传算法与被试交互式的实现调节。另一种视网膜编码器RE^＊使用特殊的时空滤波器组、决策树算法以及仿真的微小眼动算法组合构成。这种新编码器可以显著提高调节的结果。近期RE的研究集中在试图增强RE本身基于P1模式预处理的特性、模式分割、时间模式表达的选择性调整以及刺激电极簇的选择性控制。随着神经假体技术研究的不断深入和成熟,将会有越来越多的人受益。     

Can binocular rivalry reveal neural correlates of consciousness?

This essay critically examines the extent to which binocular rivalry can provide important clues about the neural correlates of conscious visual perception. Our ideas are presented within the framework of four questions about the use of rivalry for this purpose: (i) what constitutes an adequate comparison condition for gauging rivalry''s impact on awareness, (ii) how can one distinguish abolished awareness from inattention, (iii) when one obtains unequivocal evidence for a causal link between a fluctuating measure of neural activity and fluctuating perceptual states during rivalry, will it generalize to other stimulus conditions and perceptual phenomena and (iv) does such evidence necessarily indicate that this neural activity constitutes a neural correlate of consciousness? While arriving at sceptical answers to these four questions, the essay nonetheless offers some ideas about how a more nuanced utilization of binocular rivalry may still provide fundamental insights about neural dynamics, and glimpses of at least some of the ingredients comprising neural correlates of consciousness, including those involved in perceptual decision-making.     

Using Virtual Reality to Study Alcohol Intoxication Effects on the Neural Correlates of Simulated Driving

The use of virtual reality in the form of simulated tasks can provide a realistic environment in which to study complex naturalistic behaviors. Many of the behavioral effects of alcohol intoxication are well known, but there is relatively little imaging evidence examining how alcohol exposure might transiently modulate brain function, especially in the context of task performance. In this review, we provide a brief synopsis of previous work using functional magnetic resonance imaging (fMRI) to study the neural correlates of alcohol intoxication. We describe in detail two studies from our published work, the first involving a visual perception paradigm, and the second involving virtual reality through a naturalistic behavior; simulated driving. Participants received single-blind individualized doses of beverage alcohol designed to produce blood alcohol content (BAC) of 0.04 and 0.08 or placebo. Subjects were fMRI scanned after training to asymptote performance. In both studies we found specific circuits that were differentially modulated by alcohol, we revealed both global and local effects of alcohol, and we examined relationships between behavior, brain function, and alcohol blood levels.     

Emotion-perception interplay in the visual cortex: "the eyes follow the heart"

Emotive aspects of stimuli have been shown to modulate perceptual thresholds. Lately, studies using functional Magnetic Resonance Imaging (fMRI) showed that emotive aspects of visual stimuli activated not only canonical limbic regions, but also sensory areas in the cerebral cortex. However, it is still arguable to what extent such emotive, related activation in sensory areas of the cortex are affected by physical characteristic or attribute difference of stimuli. To manipulate valence of stimuli while keeping visual features largely unchanged, we took advantage of the Expressional Transfiguration (ET) of faces. In addition, to explore the sensitivity of high level visual regions, we compared repeated with unrepeated (i.e. different) stimuli presentations (fMR adaptation). Thus, the dynamics of brain responses was determined according to the relative signal reduction during repeated relative to different presentations (adaptation ratio). Our results showed, for the first time, that emotional valence produced significant differences in fMR adaptation, but not in overall levels of activation of lateral occipital complex (LOC). We then asked whether this emotion modulation on sensory cortex could be related to previous personal experience that attached negative attributes of stimuli. To clarify this, we investigated Posttraumatic Stress Disorder (PTSD) and non-PTSD veterans. PTSD is characterized by recurrent revival of trauma-related sensations. Such phenomena have been attributed to a disturbed processing of trauma-related stimuli, either at the perceptual level or at the cognitive level. We assumed that PTSD veterans would differ from non-PTSD veterans (who have similar combat experience) in their high order visual cortex responses to combat-related visual stimuli that are associated with their traumatic experience. An fMRI study measured the cerebral activation of subjects while viewing pictures with and without combat content, in repeated or different presentation conditions. The emotive effect on the visual cortex was found, again, only in the fMR-adaptation paradigm. Visual cortical regions showed significant differences between PTSD and non-PTSD veterans only in repeated presentations of trauma-related stimuli (i.e. combat). In these regions, PTSD veterans showed less decrease in signal with repeated presentations of the same combat-related stimuli. This finding points to the possibility that traumatic experience modulates brain activity at the level of sensory cortex itself.