MR Diffusion Tensor Imaging: A Window into White Matter Integrity of the Working Brain

As Norman Geschwind asserted in 1965, syndromes resulting from white matter lesions could produce deficits in higher-order functions and “disconnexion” or the interruption of connection between gray matter regions could be as disruptive as trauma to those regions per se. The advent of in vivo diffusion tensor imaging, which allows quantitative characterization of white matter fiber integrity in health and disease, has served to strengthen Geschwind’s proposal. Here we present an overview of the principles of diffusion tensor imaging (DTI) and its contribution to progress in our current understanding of normal and pathological brain function.     

扩散张量成像在弱视中应用的探讨

弱视是儿童常见眼科疾病,发病机制目前尚不完全清楚.扩散张量成像(diffusion tensor imaging,DTI)是MRI技术的一个新应用,将DTI引入弱视发病机制的研究使人们能更加直观地研究弱视患者视路相关结构有否解剖改变.正确运用哲学观点、充分发挥创新能力并灵活选用适宜技术与高新技术以期达到弱视诊断的最优化.     

扩散张量成像在脑胶质瘤诊治中的应用

扩散张量成像是目前唯一可以在活体显示大脑内白质纤维走向的磁共振成像技术,对于脑胶质瘤术前诊断,制定手术计划,指导手术及判定预后等方面是非常有帮助的.综述了近年来扩散张量成像技术在脑胶质瘤诊断、治疗及判定预后中的应用价值,并结合文献提出了目前存在的不足.     

扩散张量成像在脑胶质瘤诊治中的应用

扩散张量成像是目前唯一可以在活体显示大脑内白质纤维走向的磁共振成像技术,对于脑胶质瘤术前诊断,制定手术计划,指导手术及判定预后等方面是非常有帮助的。综述了近年来扩散张量成像技术在脑胶质瘤诊断、治疗及判定预后中的应用价值,并结合文献提出了目前存在的不足。     

跨期决策的神经机制：基于体素形态学和弥散张量成像研究的证据

目前神经经济学的首要目标是探讨人们经济决策背后的认知机制和神经基础。随着脑成像技术的发展, 人们对于脑结构和功能的认识也越来越深入。跨期决策作为经济决策领域的一个重要分支, 对其理解可以丰富决策的理论内容。首先, 梳理了关于跨期决策神经机制研究, 阐述了跨期决策的四种理论, 分别为单一评价理论(single-valuation theory)、双评价理论(dual-valuation theory)、自我控制理论(self-control theory)和自我参照加工理论(self-referential processing theory), 以及脑损伤研究证据。其次, 分别整理了基于体素形态学和弥散张量成像技术在跨期决策领域中的应用, 并揭示前额叶灰质和白质体积以及背外侧前额叶-纹状体神经纤维连接对于决策冲动性的影响。最后, 未来研究需要注意其在研究方法、认知过程、决策冲动性评估模型上的创新与突破。     

Aging Effects on Recollection and Familiarity: The Role of White Matter Hyperintensities

ABSTRACT

Previous studies have indicated that aging is associated with declines in recollection whereas familiarity-based recognition is left largely unaffected. The brain changes underlying these recollection declines are yet not well understood. In the current study we examined the role of white matter integrity as measured by white matter hyperintensities (WMH) on age-related changes in recollection and familiarity. Recognition was measured using a remember/know procedure (Experiment 1) and a source-memory process-dissociation procedure (Experiment 2). Robust age related declines in recollection were observed, but there was no evidence that white matter damage was related to the observed memory declines. Although future studies with larger samples will be necessary to fully characterize the role of WMH in normal age-related declines in different types of memory, the results suggest that declines in recollection are not strongly related to the brain changes indexed by WMHs.     

弥散张量成像在语言认知神经科学研究中的应用

人类的语言功能不仅仅基于以额叶、颞叶为代表的语言脑区灰质皮层的激活, 更重要的是基于这些脑区之间白质纤维束的连接。随着各种脑成像技术的逐渐成熟, 基于核磁共振的弥散张量成像技术在语言认知领域展现出越来越重要的作用。弥散张量成像在语言认知研究上的应用, 可以将其与行为测查、功能定位成像、功能连接、全脑网络等多种分析方法结合来共同研究语言认知, 进而从脑结构的角度来探究语言与脑的关系。     

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。     

White Matter: Organization and Functional Relevance

Norman Geschwind’s landmark paper in 1965, “Disconnexion Syndromes in Animals and Man,” inspired a generation of investigators to consider the effects of focal brain lesions disrupting higher brain functions. Although Geschwind viewed disconnection as resulting from either white or gray matter lesions, his signature article drew upon the insights of 19th century neurologists and firmly established white matter within the vocabulary of behavioral neurology, neuropsychology, and cognitive neuroscience. This influence, and the advent of sensitive neuroimaging techniques later in the 20th century, led to white matter gradually gaining more attention as an essential component of distributed neural networks subserving cognition and emotion. Today, whereas focal white matter lesions remain central to the pathogenesis of classic neurobehavioral syndromes, diffuse white matter involvement is regarded as increasingly relevant to a wide variety of dementia syndromes and a host of neuropsychiatric disorders as well. In parallel, better understanding of the neurobiology of brain white matter at all ages has been achieved. While much remains to be explored, a general conceptual formulation is that white matter supports information transfer to complement the information processing carried out by gray matter. As knowledge of the organization and functional relevance of white matter continues to advance, improved understanding of the role of myelinated tracts in higher function can be anticipated, and with it many clinical benefits.     

Modeling Intraindividual Cognitive Change in Aging Adults: Results from the Einstein Aging Studies

This paper reviews research from the longitudinal Einstein Aging Studies (EAS) that has focused on modeling intraindividual cognitive change in aging adults. We describe how to separate models of intraindividual change at the within-person level from models of individual differences in change at the between-person level. We illustrate this distinction by analyzing new data from the EAS to test the speed hypothesis at the intraindividual level of analyses. The present findings replicate those of Sliwinski and Buschke (1999) by showing that within-person changes in speed predict within-person changes in cognition, but that speed does not substantially attenuate estimates of within-person cognitive decline. We conclude that correct measurement and explanatory modeling of intraindividual change should be the primary focus of longitudinal aging research, and that the more common practice of modeling individual differences in change should be a secondary focus.     

The Relation of White Matter Hyperintensities to Cognitive Performance in the Normal Old: Education Matters

ABSTRACT

This study examined whether the severity of cerebral white matter abnormalities (evident on MR images as white matter hyperintensities (WMH)) was related to the cognitive performance of 141 high-functioning older adults. The elderly showed the typical age decrement on measures of processing speed, working memory, and inhibition; however WMH severity was significantly related only to processing speed. The strength of this relationship was, however, influenced by the educational level of the participants, such that processing speed was more associated with WMH severity in less-educated than in well-educated participants. This is consistent with recent concepts of cognitive reserve, but does raise a question as to the underlying source of the cognitive decrement found in the sort of well-educated elders typically used in cognitive-aging studies.     

Heterogeneity of Neuropsychological Impairment in HIV Infection: Contributions from Mild Cognitive Impairment

Despite longstanding acknowledgement of the heterogeneity of HIV-associated neurocognitive disorders (HAND), existing HAND diagnostic methods classify according to the degree of impairment, without regard to the pattern of neuropsychological strengths and weaknesses. Research in mild cognitive impairment (MCI) has demonstrated that classifying individuals into subtypes by both their level and pattern of impairment, using either conventional or statistical methods, has etiologic and prognostic utility. Methods for characterizing the heterogeneity of MCI provide a framework that can be applied to other disorders and may be useful in clarifying some of the current challenges in the study of HAND. A small number of studies have applied these methods to examine the heterogeneity of neurocognitive function among individuals with HIV. Most have supported the existence of multiple subtypes of neurocognitive impairment, with some evidence for distinct clinicodemographic features of these subtypes, but a number of gaps exist. Following a review of diagnostic methods and challenges in the study of HAND, we summarize the literature regarding conventional and empirical subtypes of MCI and HAND and identify directions for future research regarding neurocognitive heterogeneity in HIV infection.     

认知老化与脑：HAROLD模型之争

HAROLD模型（Hemispheric Asymmetry Reduction in Older Adults）是指与年轻人相比,老年人在完成某些认知任务时大脑激活呈现出非对称性减弱的现象。该模型自提出以来就引发了很多质疑和研究,近几年来又有一系列的研究分别从不同角度提供了支持该模型的证据,它们包括记忆研究领域、抑制研究领域、语言认知研究领域、感觉动作研究领域和脑神经研究领域。同时也存在明显不支持该模型的研究证据,主要体现为对补偿说的批驳。通过对支持该模型和不支持该模型两方面脑成像研究成果的文献分析,发现HAROLD模型可能是一个任务特异性模型;除补偿说之外,还有其他可能的观点能够解释功能性脑成像的年龄差异;对脑激活定义的进一步明确化有助于澄清相关的争论     

认知年老化与执行衰退假说

在认知年老化领域,执行衰退假说是近年来新兴的一种理论。执行衰退假说在理论上具有很强的吸引力,但在实证研究中却存在很多困难,如执行功能的可分离性问题,执行功能测量的信度和效度问题,以及执行功能与加工速度的关系问题。目前,该领域研究的焦点是：在行为学水平上,控制一般性因素（加工速度）后,执行功能是否仍对认知年老化起重要的中介作用;在神经水平上,执行（额叶）功能随龄的变化情况,以及在认知年老化过程中,额叶在大脑功能重组中扮演的角色。最终实现对认知年老化的理解,需要将认知功能与大脑结构联系起来;既看到广泛存在的共同的基本机制,又不能忽略不同认知结构的选择性变化。     

White Matter Hyperintensities and Working Memory: An Explorative Study

ABSTRACT

White matter hyperintensities (WMH) are commonly observed in elderly people and may have the most profound effect on executive functions, including working memory. Surprisingly, the Digit Span backward, a frequently employed working memory task, reveals no association with WMH. In the present study, it was investigated whether more detailed analyses of WMH variables and study sample selection are important when establishing a possible relationship between the Digit Span backward and WMH. To accomplish this, the Digit Span backward and additional working memory tests, WMH subscores, and cardiovascular risk factors were examined. The results revealed that performance on the Digit Span backward test is unrelated to WMH, whereas a relationship between other working memory tests and WMH was confirmed. Furthermore, a division between several white matter regions seems important; hyperintensities in the frontal deep white matter regions were the strongest predictor of working memory performance.     

认知储备的测量及其在认知老化中的应用

认知储备是指个体自适应利用神经网络对不断增加的脑损伤进行补偿的能力, 它能显著影响个体的生理功能、认知功能和行为结果。当前有关认知储备的研究主要集中在认知储备的测量及其在认知老化研究中的应用方面。现有研究尽管已在认知储备的测量及其与认知老化的关系上取得越来越多的共识, 但在诸如认知储备测量的标准化、认知储备与认知衰退率、认知储备与脑病理的关系等问题上还存在较大争议。未来研究除应进一步标准化对认知储备的测量, 进而探讨认知储备的病理机制, 还应关注认知储备对老化的干预研究。