Wang Rongpin, Wilkinson Molly, Kane Tara, Takahashi Emi
Division of Newborn Medicine, Department of Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA, United States.
Department of Radiology, Guizhou Provincial People's Hospital, Guiyang, China.
Front Neurosci. 2017 Nov 1;11:576. doi: 10.3389/fnins.2017.00576. eCollection 2017.
There has been evidence that during brain development, emerging thalamocortical (TC) and corticothalamic (CT) pathways converge in some brain regions and follow each other's trajectories to their final destinations. Corpus callosal (CC) pathways also emerge at a similar developmental stage, and are known to converge with TC pathways in specific cortical regions in mature brains. Given the functional relationships between TC and CC pathways, anatomical convergence of the two pathways are likely important for their functional integration. However, it is unknown (1) where TC and CT subcortically converge in the human brain, and (2) where TC and CC converge in the cortex of the human brain, due to the limitations of non-invasive methods. The goals of this study were to describe the spatio-temporal relationships in the development of the TC/CT and CC pathways in the human brain, using high-angular resolution diffusion MR imaging (HARDI) tractography. Emerging cortical, TC and CC pathways were identified in fetal brains ranging from 17 gestational weeks (GW) to 30 GW, as well as 34-40 GW newborns. Some pathways from the thalami were found to be converged with pathways from the cerebral cortex as early as 17 GW. Such convergence was observed mainly in anterior and middle regions of the brain until 21 GW. At 22 GW and onwards, posterior pathways from the thalami also converged with cortical pathways. Many CC pathways reached the full length up to the cortical surface as early as 17 GW, while pathways linked to thalami (not only TC axons but also including pathways linked to thalamic neuronal migration) reached the cortical surface at and after 20 GW. These results suggest that CC pathways developed earlier than the TC pathways. The two pathways were widespread at early stages, but by 40 GW they condensed and formed groups of pathways that projected to specific regions of the cortex and overlapped in some brain regions. These results suggest that HARDI tractography has the potential to identify developing TC/CT and CC pathways with the timing and location of their convergence in fetal stages persisting in postnatal development.
有证据表明，在大脑发育过程中，新兴的丘脑皮质（TC）和皮质丘脑（CT）通路在某些脑区汇聚，并沿着彼此的轨迹到达最终目的地。胼胝体（CC）通路也在相似的发育阶段出现，并且已知在成熟大脑的特定皮质区域与TC通路汇聚。鉴于TC和CC通路之间的功能关系，这两条通路的解剖学汇聚可能对它们的功能整合很重要。然而，由于非侵入性方法的局限性，尚不清楚（1）在人类大脑中TC和CT在皮质下何处汇聚，以及（2）在人类大脑皮质中TC和CC在何处汇聚。本研究的目的是使用高角分辨率扩散磁共振成像（HARDI）纤维束成像来描述人类大脑中TC/CT和CC通路发育的时空关系。在妊娠17周（GW）至30 GW的胎儿大脑以及34 - 40 GW的新生儿中识别出新兴的皮质、TC和CC通路。早在17 GW时，就发现一些来自丘脑的通路与来自大脑皮质的通路汇聚。这种汇聚主要在大脑的前部和中部区域观察到，直到21 GW。在22 GW及以后，来自丘脑的后部通路也与皮质通路汇聚。许多CC通路早在17 GW时就延伸至皮质表面的全长，而与丘脑相连的通路（不仅包括TC轴突，还包括与丘脑神经元迁移相关的通路）在20 GW及以后到达皮质表面。这些结果表明CC通路比TC通路发育得更早。这两条通路在早期广泛分布，但到40 GW时它们浓缩并形成投射到皮质特定区域并在某些脑区重叠的通路组。这些结果表明，HARDI纤维束成像有潜力识别发育中的TC/CT和CC通路，以及它们在胎儿期汇聚的时间和位置，并持续到出生后发育阶段。
