脑白质功能——来自BOLD-fMRI的证据

White Matter Function——Evidences From BOLD-fMRI Studies

白质是组成大脑神经网络不可缺少的部分,对白质的探索多采用解剖形态学方法.血氧水平依赖功能性磁共振成像(blood oxygen level dependent functional magnetic resonance imaging,BOLD-fMRI)作为一种研究大脑功能的非侵入性工具已得到了广泛的应用,但是大多数BOLD-fMRI研究集中在大脑灰质,将白质BOLD信号作为噪声处理.事实上,白质的BOLD信号允许我们探索其动态功能特性,构建白质的功能连接网络,进而从功能角度来评估白质的完整性.因此,在已有研究基础上,我们对白质功能研究相对较少的原因以及BOLD信号可能的神经生理基础进行探讨,并概述了近年来已经发表的相关证据.最后,我们梳理了白质BOLD-fMRI研究存在的问题以及未来研究方向.

White matter,which constituted the anatomical connections between brain regions,accounted for approximately 50%of the human brain.The crucial role of the intact white matter connections for normal brain function has been described by extensive lesion and anatomic studies.Although traditional structural techniques,such as diffusion tensor imaging(DTI),can successfully explore the white matter architecture,they failed to uncover neural activity and dynamics occurring in white matter.Blood oxygen level dependent functional magnetic resonance imaging(BOLD-fMRI)is a noninvasive technique to map brain activation and connectivity.Previous BOLD-fMRI studies primarily focused on spontaneous activity in gray matter rather than that in white matter,since white matter fMRI activation remained controversial.However,the evidence is accumulating for fMRI activation in white matter.This paper reviewed former researches on spontaneous activity in white matter,including physiological bases,neurovascular and neurometabolic coupling,brain activation,and brain connectivity.Despite the differences observed in vascular density between gray matter and white matter,BOLD effects in white matter were reported to be related to neural activity.Robust BOLD activations were detected in the posterior limb of internal capsule,anterior corpus callosum,etc.The power spectrum of resting-state white matter BOLD signals was associated with white matter density and fraction anisotropy(FA)rather than random distribution as noise.Besides,regarding to the functional connectivity of white matter,it was well established that white matter manifested an intrinsic functional organization as interacting networks of functional modules.Moreover,the functional networks of white matter were closely related to that of gray matter and white matter tracts.Several brain disorders,such as mild cognitive impairment,schizophrenia,Alzheimer’s and Parkinson disease,were characterized by functional connectivity abnormalities of white matter.Finally,the recommendations and suggestions for future study were included on the neurophysiological basis of white matter BOLD-fMRI signal using multimode imaging data and the common abnormalities in white matter across multiple psychiatric disorders.