Montreal Neurological Institute, McGill University, Montreal, Québec, Canada.
Hum Brain Mapp. 2013 Jul;34(7):1685-95. doi: 10.1002/hbm.22018. Epub 2012 Feb 22.
Typical adults show an inverse relation between callosal fiber length and degree of interhemispheric connectivity. This has been hypothesized to be a consequence of the influence of conduction delays and cellular costs during development on axonal pruning, both of which increase with fiber length. Autism spectrum disorder (ASD) provides a test of this hypothesis: Children with ASD are known to have enlarged brains; thus, adults with ASD should show reductions in interhemispheric connectivity proportional to their degree of brain overgrowth during development. This prediction was tested by assessing the relation between both the size and structure of the corpus callosum and callosal fiber length, adjusting for intracranial volume, which is thought to reflect maximum brain size achieved during development. Using tractography to estimate the length of callosal fibers emanating from all areas of cortex, and through which region of the corpus callosum they pass, we show that adults with ASD show an inverse relation between callosal fiber length, adjusted for intracranial volume, and callosum size, and a positive relation between adjusted callosal fiber length and radial diffusivity. The results provide support for the hypothesized impact of fiber length during development.
典型的成年人在胼胝体纤维长度和大脑两半球间连接程度之间表现出一种相反的关系。这种关系被假设是由于在发育过程中，传导延迟和细胞成本对轴突修剪的影响，而这两者都随着纤维长度的增加而增加。自闭症谱系障碍（ASD）为这一假说提供了一个检验：众所周知，患有 ASD 的儿童大脑较大；因此，患有 ASD 的成年人在大脑发育过程中的脑过度生长程度应该与大脑两半球间连接程度的降低成比例。这一预测通过评估胼胝体的大小和结构与胼胝体纤维长度之间的关系来检验，同时考虑了脑内总体积，这被认为反映了发育过程中达到的最大脑容量。通过追踪技术来估计源自大脑所有区域的胼胝体纤维的长度，以及它们穿过胼胝体的区域，我们发现 ASD 成年人的胼胝体纤维长度与脑内总体积调整后呈反比关系，与胼胝体大小呈反比关系，与调整后的胼胝体纤维长度与辐射状弥散度呈正相关。这些结果为发育过程中纤维长度的假设影响提供了支持。
