Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands; Radboudumc, Department of Anatomy, Nijmegen, The Netherlands; University of Oxford, Oxford Centre for Functional MRI of the Brain, Oxford, UK.
Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.
Neuroimage. 2015 Apr 1;109:378-87. doi: 10.1016/j.neuroimage.2015.01.001. Epub 2015 Jan 10.
Gyrification of the human cerebral cortex allows for the surface expansion that accommodates many more cortical neurons in comparison to other mammals. For neuroimaging, however, it forms a feature that complicates analysis. For example, it has long been established that cortical layers do not occupy the same depth in gyri and sulci. Recently, in vivo diffusion imaging has provided insights into the fibre architecture of the cortex, usually showing radial tensor orientations. This makes it relevant to investigate whether cortical diffusion tensor metrics depend on the gyral pattern. High-resolution (1mm isotropic) diffusion weighted MRI of the medial wall of the hemispheres was performed at 7 T. Diffusion data were resampled to surfaces in the cortex and underlying white matter, where the cortical surfaces obeyed the equivolume principle for cortical laminae over the cortical curvature. Diffusion tensor metrics were averaged over bins of curvature to obtain maps of characteristic patterns in the gyrus. Diffusivity, anisotropy and radiality varied with curvature. Radiality was maximal in intermediate layers of the cortex next to the crown of the gyrus, not in white matter or on the crown. In the fundus, the deep cortical layers had tangential tensor orientations. In the white matter, tensor orientation changed from radial on the crown to tangential under the banks and fundus. White matter anisotropy gradually increased from the crown to the fundus. The characteristic pattern in the gyrus demonstrated here is in accordance with ex vivo diffusion MR microscopy and histological studies. The results indicate the necessity of taking into account the gyral pattern when cortical diffusion data is analysed. Additionally, the data suggest a confound for tractography approaches when reaching the gyrus, resulting in a possible bias towards the gyral crown. The implications for mechanisms that could drive cortical folding are discussed.
人类大脑皮层的回旋结构允许表面积扩大，与其他哺乳动物相比，能够容纳更多的皮质神经元。然而，对于神经影像学来说，它形成了一个使分析变得复杂的特征。例如，长期以来，人们已经确立了皮质层在脑回和脑沟中并不占据相同的深度。最近，活体扩散成像为皮层纤维结构提供了新的见解，通常显示出放射张量方向。这使得研究皮质扩散张量指标是否依赖于脑回模式变得相关。在 7T 上对半球内侧壁进行了高分辨率（1 毫米各向同性）弥散加权 MRI。将扩散数据重新采样到皮层和下白质的表面，其中皮层表面在皮层曲率上遵循皮层层的等体积原则。在曲率的bins 上平均扩散张量指标，以获得脑回中特征模式的图谱。扩散性、各向异性和放射状随曲率而变化。放射状在靠近脑回冠部的皮层中间层最大，而不在白质或脑回冠部。在底部，深部皮层层具有切向张量方向。在白质中，张量方向从脑回冠部的放射状变为脑回bank 和底部的切向。白质各向异性从脑回冠部逐渐增加到底部。这里显示的脑回特征模式与离体扩散 MR 显微镜和组织学研究一致。结果表明，在分析皮质扩散数据时，必须考虑脑回模式。此外，当到达脑回时，数据表明追踪方法存在混淆，可能导致偏向脑回冠部的潜在偏差。讨论了可能导致皮质折叠的机制的影响。
