Emerson Robert W, Gao Wei, Lin Weili
Department of Radiology and Biomedical Research Imaging Center and.
Carolina Institute for Developmental Disabilities, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, and.
J Neurosci. 2016 Oct 19;36(42):10883-10892. doi: 10.1523/JNEUROSCI.3980-15.2016.
Asymmetry in the form of left-hemisphere lateralization is a striking characteristic of the cerebral regions involved in the adult language network. In this study, we leverage a large sample of typically developing human infants with longitudinal resting-state functional magnetic resonance imaging scans to delineate the trajectory of interhemispheric functional asymmetry in language-related regions during the first 2 years of life. We derived the trajectory of interhemispheric functional symmetry of the inferior frontal gyrus (IFG) and superior temporal gyrus (STG), the sensory and visual cortices, and two higher-order regions within the intraparietal sulcus and dorsolateral prefrontal cortex. Longitudinal models revealed a best fit with quadratic age terms and showed significant estimated coefficients of determination for both the IFG (r = 0.261, p < 0.001) and the STG (r = 0.142, p < 0.001) regions while all other regions were best modeled by log-linear increases. These inverse-U-shaped functions of the language regions peaked at ∼11.5 months of age, indicating that a transition toward asymmetry began in the second year. This shift was accompanied by an increase in the functional connectivity of these regions within the left hemisphere. Finally, we detected an association between the trajectory of the IFG and language outcomes at 4 years of age (χ = 10.986, p = 0.011). Our results capture the developmental timeline of the transition toward interhemispheric functional asymmetry during the first 2 years of life. More generally, our findings suggest that increasing interhemispheric functional symmetry in the first year might be a general principle of the developing brain, governing different functional systems, including those that will eventually become lateralized in adulthood.
Cross-sectional studies of the language system in early infancy suggest that the basic neural mechanisms are in place even before birth. This study represents the first of its kind, using a large longitudinal sample of infants, to delineate the early language-related transition toward interhemispheric functional asymmetry in the brain using resting-state functional MRI. More generally, our findings suggest that increasing interhemispheric functional symmetry in the first year might be a general principle of the developing brain governing multiple functional systems, including those that will eventually become lateralized in adulthood. Although resting-state functional MRI cannot provide direct insights into the developmental mechanisms of language lateralization, this study reveals language-related functional connectivity changes during infancy, marking critical points in the development of the brain's functional architecture.
以左半球偏侧化为形式的不对称性是参与成人语言网络的脑区的一个显著特征。在本研究中，我们利用大量典型发育的人类婴儿的纵向静息态功能磁共振成像扫描数据，来描绘生命最初两年中语言相关区域半球间功能不对称性的发展轨迹。我们得出了额下回（IFG）、颞上回（STG）、感觉和视觉皮层以及顶内沟和背外侧前额叶皮层内两个高阶区域的半球间功能对称性轨迹。纵向模型显示与二次年龄项拟合最佳，并且显示出IFG（r = 0.261，p < 0.001）和STG（r = 0.142，p < 0.001）区域的显著估计决定系数，而所有其他区域由对数线性增长拟合最佳。语言区域的这些倒U形函数在约11.5个月大时达到峰值，表明向不对称性的转变在第二年开始。这种转变伴随着这些区域在左半球内功能连接性的增加。最后，我们在4岁时检测到IFG轨迹与语言结果之间的关联（χ = 10.986，p = 0.011）。我们的结果描绘了生命最初两年中向半球间功能不对称性转变的发育时间表。更一般地说，我们的发现表明，第一年中半球间功能对称性的增加可能是发育中大脑的一个普遍原则，支配着不同的功能系统，包括那些最终在成年期会发生偏侧化的系统。
对婴儿早期语言系统的横断面研究表明，基本神经机制甚至在出生前就已存在。本研究是同类研究中的首个，使用大量婴儿纵向样本，利用静息态功能磁共振成像描绘大脑中与早期语言相关的向半球间功能不对称性的转变。更一般地说，我们的发现表明，第一年中半球间功能对称性的增加可能是发育中大脑支配多个功能系统的一个普遍原则，包括那些最终在成年期会发生偏侧化的系统。虽然静息态功能磁共振成像不能直接洞察语言偏侧化的发育机制，但本研究揭示了婴儿期与语言相关的功能连接变化，标志着大脑功能结构发育中的关键点。
