日前，美国加州大学洛杉矶分校的一组研究人员运用一种新型的脑成像扫描仪发现，人类智商在很大程度上与大脑神经的轴突及其走向和位置相关，而这些特征则主要由基因控制。相关研究刊登在最近一期《神经学》杂志上。
研究人员发现，基因似乎通过决定进入髓磷脂中大脑神经轴突的数量来影响智商。覆盖在神经轴突外的髓磷脂主要由脂肪构成，可使快速信号直接进入大脑。髓磷脂越厚，神经冲动越快。
负责该项研究的加州大学洛杉矶分校副教授保罗•汤普森和他的同事使用了一种被称为“哈尔迪”（HARDI：高分辨率漫射成像仪）的大脑扫描仪，分别对23对同卵双胞胎和异卵双胞胎进行了大脑扫描。该扫描仪类似于对类固醇进行扫描的高分辨率核磁共振成像仪，但速度更快，分辨率更高。核磁共振扫描仪主要用来测量脑容量，而“哈尔迪”则通过追踪经过脑白质的信号来测量髓磷脂的数量。如果信号在一个特定的方向快速扩散，说明大脑处理信息速度快。如果信号扩散没有明确的方向性，则说明智力略低。
研究人员发现，大脑回路中髓磷脂形成的轨迹如同一个倒置的U形，高峰在中年，而后就开始慢慢下降。汤普森认为，找出那些能够促进生成高含量髓磷脂的基因，将对预防一些脑部疾病的发生起重要作用，如多发性硬化症和孤独症，这些疾病都与髓磷脂的受损相关。
原始出处：The Journal of Neuroscience, February 18, 2009, doi:10.1523/JNEUROSCI.4184-08.2009
Genetics of Brain Fiber Architecture and Intellectual Performance
Ming-Chang Chiang,1 Marina Barysheva,1 David W. Shattuck,1 Agatha D. Lee,1 Sarah K. Madsen,1 Christina Avedissian,1 Andrea D. Klunder,1 Arthur W. Toga,1 Katie L. McMahon,2 Greig I. de Zubicaray,2 Margaret J. Wright,3 Anuj Srivastava,4 Nikolay Balov,4 and Paul M. Thompson1
1Laboratory of Neuro Imaging, Department of Neurology, University of California, Los Angeles, School of Medicine, Los Angeles, California 90095-7334, 2University of Queensland, Functional Magnetic Resonance Imaging Laboratory, Centre for Magnetic Resonance, Brisbane, Queensland 4072, Australia, 3Queensland Institute of Medical Research, Brisbane, Queensland 4029, Australia, and 4Department of Statistics, Florida State University, Tallahassee, Florida 32306
Correspondence should be addressed to Dr. Paul M. Thompson, Laboratory of Neuro Imaging, Department of Neurology, University of California, Los Angeles, School of Medicine, 635 Charles E. Young Drive South, Suite 225E, Los Angeles, CA 90095-7334.
The study is the first to analyze genetic and environmental factors that affect brain fiber architecture and its genetic linkage with cognitive function. We assessed white matter integrity voxelwise using diffusion tensor imaging at high magnetic field (4 Tesla), in 92 identical and fraternal twins. White matter integrity, quantified using fractional anisotropy (FA), was used to fit structural equation models (SEM) at each point in the brain, generating three-dimensional maps of heritability. We visualized the anatomical profile of correlations between white matter integrity and full-scale, verbal, and performance intelligence quotients (FIQ, VIQ, and PIQ). White matter integrity (FA) was under strong genetic control and was highly heritable in bilateral frontal (a2 = 0.55, p = 0.04, left; a2 = 0.74, p = 0.006, right), bilateral parietal (a2 = 0.85, p < 0.001, left; a2 = 0.84, p < 0.001, right), and left occipital (a2 = 0.76, p = 0.003) lobes, and was correlated with FIQ and PIQ in the cingulum, optic radiations, superior fronto-occipital fasciculus, internal capsule, callosal isthmus, and the corona radiata (p = 0.04 for FIQ and p = 0.01 for PIQ, corrected for multiple comparisons). In a cross-trait mapping approach, common genetic factors mediated the correlation between IQ and white matter integrity, suggesting a common physiological mechanism for both, and common genetic determination. These genetic brain maps reveal heritable aspects of white matter integrity and should expedite the discovery of single-nucleotide polymorphisms affecting fiber connectivity and cognition.
