脑功能磁共振伦理学问题初探

本文概略介绍新兴的脑功能磁共振检查原理及其对人脑运作机制、人类精神活动的研究.讨论脑功能磁共振的临床技术是否完善、现阶段普及该技术是否可能和必要,以及进行脑功能磁共振检查可能引发的隐私权、歧视等伦理学问题,并探讨解决之道.     

认知风格分型的神经基础:静息态fMRI研究

认知风格是个体习惯性的加工偏好。行为研究和任务态的功能成像研究已为认知风格分型理论提供了丰富的依据,但关于个体安静无任务状态下的脑活动是否也能表现出认知风格上的差异仍知之甚少。本研究使用静息态功能磁共振(f MRI)技术,以在校大学生为研究对象,以较为严格的标准使用认知风格分型任务分离出整体型和分析型认知风格被试,通过分析两组被试局部脑活动的一致性和整体脑活动的功能连接性,考察了静息条件下认知风格分型的神经基础。结果发现,不同认知风格群体的脑局部和整体活动均可能存在差异。个体越偏向分析型认知风格,左侧小脑的激活越强;左侧小脑与双侧大脑的功能区有更强、更广泛的连接。结果提示,安静无任务下个体的脑活动也可能表现出认知风格上的差异。     

从脑研究中挖掘新信息

功能磁共振成像技术研究脑机制的重要手段,并被广泛地应用在最近三年发表的研究精神疾病脑机制的论文中,有约一半以上以功能磁共振成像技术为研究手段。功能磁共振成像以很高的速率获取随时间变化的幅脑图像,因而具有很高的空间分辨率和较高的时间分辨率。     

人类大脑结构和功能的性别差异：来自脑成像研究的证据

大脑的性别差异近年来受到了广泛关注。脑成像技术的出现为脑结构和脑功能性别差异的研究开辟了新的道路。借助结构磁共振成像和弥散张量成像等脑结构信息, 以及脑电图、正电子发射断层扫描技术和功能性磁共振成像等脑功能信息, 当前研究主要探讨了脑灰质、脑白质和大脑的基线活动在脑局部区域、脑子系统、全脑连接组三个层次上的性别差异及其在年龄上的发展变化。此外, 为了更好地理解脑性别差异, 当前文章还探讨了脑性别差异研究领域的一些认识误区。有关脑性别差异的研究虽然已经取得了丰富的成果, 但现有的研究结果存在很多分歧, 仍然有深入挖掘的空间。未来应该加强对具有性别特异性的心理疾病脑机制的研究, 关注基因和环境对脑性别差异的交互作用, 并利用脑功能活动动态变化的特性、以及结合多模态的脑成像技术进一步阐明脑性别差异。     

舞动治疗：一种自下而上的精神分裂症干预探索

皮层-基底节-丘脑网络与脑岛网络属于感觉运动相关网络, 这两个网络的改变可能是导致精神分裂症的重要原因。目前主流研究与临床干预聚焦于患者的高级脑区异常, 对感觉运动系统的关注不足。对健康个体的研究发现舞蹈训练对感觉运动相关脑网络具有显著提升作用, 并自下而上地促进高级功能。以上研究提示舞蹈训练可能是干预精神分裂症、改善患者认知功能的新途径。本研究拟借助多模态磁共振成像技术, 以精神分裂症感觉运动相关网络为着力点, 通过分析精神分裂症患者在舞蹈训练前后的脑影像、临床症状及认知行为的改变, 揭示舞蹈训练临床干预的神经机制。     

认知心理生理学与无创性脑功能成像技术

无创性脑功能成像技术是认知心理生理学研究的重要手段。脑电图、事件相关电位、脑磁图、正电子发射断层摄影术、单光子发射计算机断层摄影术、功能磁共振成像和功能红外线成像等技术通过对人脑的电磁、新陈代谢、血流量、氧消耗、神经元活动等的测量来研究如视觉、注意、记忆、语言等认知活动及其与相关脑机制的相互关系。它们各有优缺点。     

利用脑成像多体素模式分析解码认知的神经表征:原理和应用

多体素模式分析(multi-voxel pattern analysis,MVPA)是一种基于机器学习理论发展出来的新的功能磁共振数据分析技术。MVPA技术通过训练分类器,对由不同认知状态引起的多体素信号模式进行分类。与传统的基于单个体素的分析方法相比,该技术可更敏感地检测脑对认知状态的表征,并使得从神经信号解码认知状态成为可能。文章介绍MVPA技术的基本原理、分析步骤以及可以用MVPA来解决的科学问题,并对应用中可能面临的问题提供了参考建议。     

失眠患者静息态脑网络的改变：网络内与网络间的功能连接异常

失眠已成为现代人群中的一种高发健康问题。静息态功能磁共振以其数据采集便利性和无创性, 成为失眠研究的主要成像手段之一。基于近年来静息态功能磁共振的发现, 失眠患者存在前额叶、颞叶、前扣带回、脑岛等认知-情绪神经环路的异常。大尺度脑网络是涵盖多个脑区、功能相对单一的大脑结构。失眠患者存在默认网络、突显网络、认知控制网络和负性情绪网络内部活动与连接异常, 而且呈现出以默认网络为核心, 包含认知控制网络、突显网络、负性情绪网络的网络间连接异常模式。此外, 结合症状、治疗和大尺度脑网络的视角, 可为失眠的“精准治疗”提供神经理论依据。未来研究可结合大数据和多模态分析技术, 验证静息态功能磁共振已有发现。而失眠的纵向追踪和队列研究会有利于进一步阐释失眠的神经机制。     

疼痛恐惧的形成及其对疼痛知觉的影响

脑岛、杏仁核是疼痛恐惧形成的重要神经网络中心。疼痛恐惧增强了慢性疼痛患者的疼痛知觉体验, 进而加剧抑郁、焦虑情绪和功能损伤程度。脑岛、杏仁核、前额皮层和前扣带回是疼痛恐惧影响疼痛知觉的重要神经基础。通过认知方法干预疼痛恐惧可以改善患者的抑郁、焦虑情绪, 减少功能损伤。未来研究应拓展疼痛恐惧的测量工具, 采用功能磁共振成像技术进一步揭示疼痛恐惧影响慢性疼痛患者疼痛知觉的神经机制。     

人脑自适应多尺度功能连接的性别差异

已有脑成像研究展示了男女脑功能差异, 但功能磁共振信号的频率划分通常基于主观经验, 使脑功能性别差异的生物学解释遭遇瓶颈。本文提出人脑自适应多尺度功能连接算法, 刻画功能连接的时空多尺度特性, 揭示出0.06~0.10 Hz的性别差异：男性较强的连接主要与边缘网络和腹侧注意网络有关, 女性较强的连接主要与腹侧注意网络、视觉网络和额顶网络有关。     

Developmental neuroimaging of children using magnetic resonance techniques

Cognitive and motor development in children remain fascinating processes that are uniquely human. Progress has been made in recent years in elucidating the prenatal process of human brain development. In addition, much information exists regarding the behavioral aspects of postnatal human development. However, little is known about the relationship between anatomic postnatal central nervous system development and the accretion of functional milestones observed in children from the neonatal period through adolescence. Recently, powerful qualitative and quantitative magnetic resonance techniques have been developed that will permit detailed inquiry into the connection between the developing brain and the developing mind. In this review, first, the steps of prenatal and postnatal brain development are reviewed briefly. Subsequently, recent magnetic resonance imaging data related to human brain development during the fetal, neonatal, and later childhood periods are presented. Finally, functional magnetic resonance imaging (fMRI) is discussed. Specific examples of its usefulness are provided. Magnetic resonance imaging techniques such as quantitative MRI, volumetric MRI, diffusion tensor imaging, and functional magnetic resonance imaging (fMRI) when combined with neurologic and neuropsychologic evaluation, will provide new insights into the cognitive development of children. MRDD Research Reviews 6:68-80, 2000.     

Exploring the neural basis of cognition: multi-modal links between human fMRI and macaque neurophysiology

Although functional magnetic resonance imaging (fMRI) with sophisticated behavioral paradigms has enabled the investigation of increasingly higher-level cognitive functions in humans, these studies seem to lose touch with neurophysiological studies in macaque monkeys. The application of fMRI and other MRI-based techniques to macaque brains allows studies in the two species to be linked. fMRI in human and macaque subjects using equivalent cognitive tasks enables direct comparisons of the functional brain architecture, even for high-level cognitive functions. Combinations of functional or structural MRI and microelectrode techniques provide ways to explore functional brain networks at multiple spatiotemporal scales. These approaches would illuminate the neurophysiological underpinnings of human cognitive functions by integrating human functional neuroimaging with macaque single-unit recordings.     

The role of neuronal signaling in controlling cerebral blood flow

Well-regulated blood flow within the brain is vital to normal function. The brain's requirement for sufficient blood flow is ensured by a tight link between neural activity and blood flow. The link between regional synaptic activity and regional cerebral blood flow, termed functional hyperemia, is the basis for several modern imaging techniques that have revolutionized the study of human brain activity. Here, we review the mechanisms of functional hyperemia and their implications for interpreting the blood oxygen level-dependent (BOLD) contrast signal used in functional magnetic resonance imaging (fMRI).     

Integrating electrophysiology and neuroimaging in the study of human cognition

Noninvasive recordings of electrical and magnetic fields generated by neuronal activity have helped to characterize the temporal sequencing and mechanisms underlying human cognition. Progress is being made toward the goal of localizing the intracranial loci at which many important electromagnetic signals are generated through the use of new analytic techniques and of scalp recordings of electromagnetic activity in neurological patients and through related work in animals. Such methods alone, however, do not yet have the three-dimensional spatial resolution that is necessary in order to identify the intracranial anatomical structures that are involved in the generation of externally recorded activity and, thus, cannot yet inform us with precision about the anatomical substrates of neural events. In comparison, neuroimaging methods, such as positron emission tomography and functional magnetic resonance imaging, can provide higher spatial resolution information about which brain structures are involved in perceptual, motor, and cognitive processes. However, these imaging methods do not yield much information about the time course of brain activity. One promising approach is to combine electromagnetic recordings and functional neuroimaging in order to gain knowledge about the spatiotemporal organization of human cognition. Here we review how electrophysiology and functional neuroimaging can be combined in the study of attention in normal humans.     

Fiber tracking using magnetic resonance diffusion tensor imaging and its applications to human brain development

Diffusion tensor imaging is unique in its ability to noninvasively visualize white matter fiber tracts in the human brain in vivo. Diffusion is the incoherent motion of water molecules on a microscopic scale. This motion is itself dependent on the micro-structural environment that restricts the movement of the water molecules. In white matter fibers there is a pronounced directional dependence on diffusion. With white matter fiber tracking or tractography, projections among brain regions can be detected in the three-dimensional diffusion tensor dataset according to the directionality of the fibers. Examples of developmental changes in diffusion, tracking of major fiber tracts, and examples of how diffusion tensor tractography and functional magnetic resonance imaging can be combined are provided. These techniques are complimentary and allow both the identification of the eloquent areas of the brain involved in specific functional tasks, and the connections between them. The noninvasive nature of magnetic resonance imaging will allow these techniques to be used in both longitudinal developmental and diagnostic studies. An overview of the technique and preliminary applications are presented, along with its current limitations.     

Cholinergic modulation of learning and memory in the human brain as detected with functional neuroimaging

The advent of neuroimaging methods such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) has provided investigators with a tool to study neuronal processes involved in cognitive functions in humans. Recent years have seen an increasing amount of studies which mapped higher cognitive functions to specific brain regions. These studies have had a great impact on our understanding of neuroanatomical correlates of learning and memory in the living human brain. Recently, advances were made to go beyond the use of fMRI as a pure cognitive brain mapping device. One of these advances includes the use of psychopharmacological approaches in conjunction with neuroimaging. The paper will introduce the combination of neuroimaging and psychopharmacology as a tool to study neurochemical modulation of human brain function. A review of imaging studies using cholinergic challenges in the context of explicit and implicit learning and memory paradigms is provided which show that cholinergic neurotransmission modulates task-related activity in sensory and frontal cortical brain areas.     

Functional neuroimaging studies of human emotions

Neuroimaging studies with positron emission tomography and functional magnetic resonance imaging have begun to describe the functional neuroanatomy of human emotion. Taken separately, specific studies vary in task dimensions and in type(s) of emotion studied, and are limited by statistical power and sensitivity. By examining findings across studies in a meta-analysis, we sought to determine if common or segregated patterns of activations exist in different emotions and across various emotional tasks. We surveyed over 55 positron emission tomography and functional magnetic resonance imaging activation studies, which investigated emotion in healthy subjects. This paper will review observations in several regions of interest in limbic (eg, amygdala, anterior cingulate cortex) and paralimbic (eg, medial prefrontal cortex, insula) brain regions in emotional responding.     

Growth of white matter in the adolescent brain: Myelin or axon?

White matter occupies almost half of the human brain. It contains axons connecting spatially segregated modules and, as such, it is essential for the smooth flow of information in functional networks. Structural maturation of white matter continues during adolescence, as reflected in age-related changes in its volume, as well as in its microstructure. Here I review recent observations obtained with magnetic resonance imaging in typically developing adolescents and point out some of the known variations in structural properties of white matter vis-à-vis brain function in health and disease. I conclude by re-focusing the interpretations of MR-based studies of white matter from myelin to axon.     

The cerebral representation of space: insights from functional imaging data

Functional imaging techniques, such as positron emission tomography and functional magnetic resonance imaging, present a unique opportunity to examine, in humans, the cerebral representation of space in vivo. Space is ubiquitous and not a unitary phenomenon, and the brain uses visual, vestibular and proprioceptive inputs to produce multiple representations of space subserving spatial cognition, ranging from gaze control to remembering multiple complex large-scale environments. Functional imaging studies have shown the importance of the parietal cortex in perceptual, motor, attention and working memory aspects of body-centred human spatial cognition. Functional imaging has also revealed pathways in humans homologous to those found in monkeys for the separate processing of spatial location and object identity. There are further suggestions of similar differentiation in working memory. The importance of the medial temporal region in the recall of spatial location has been confirmed also and novel virtual reality paradigms are now providing insights into the cerebral representation of spatially-extended large-scale environments. We still have much to learn about the cerebral representation of space in the human brain and functional brain imaging, in concert with patient studies and animal models, will allow us to continue investigating.