Characterizing axonal myelination within the healthy population: a tract-by-tract mapping of effects of age and gender on the fiber g-ratio.
Characterizing axonal myelination within the healthy population: a tract-by-tract mapping of effects of age and gender on the fiber g-ratio.
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DOI：
10.1016/j.neurobiolaging.2016.09.016
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发表时间：
2017-01
影响因子：
4.2
通讯作者：
Bozzali M
中科院分区：
文献类型：
--
作者：
Cercignani M;Giulietti G;Dowell NG;Gabel M;Broad R;Leigh PN;Harrison NA;Bozzali M
g比等于有髓鞘轴突的内径与外径的比率，与传导速度相关，因此反映了轴突的功能和完整性。现在可以使用MRI估计体内的“总”g比。本研究的目的是评估健康个体大脑中MRI衍生的纤维g-比率的变化，并表征其在整个生命周期中的变化。招募了38名年龄在20至76岁之间的健康参与者。计算全脑g-比率图并逐体素分析。还提取了中位束g比值。没有发现性别的显着影响，而年龄被发现显着相关的g-比率内的白色的问题。特定区域的分析表明，这种关系遵循一个接近线性的增长，虽然斜率似乎略有放缓后，第六个十年的生活。最有可能的解释是，在整个成年期，髓磷脂的减少是微妙但一致的，轴突的密度在第4和第5个十年之间开始减少。
The g-ratio, equal to the ratio of the inner-to-outer diameter of a myelinated axon, is associated with the speed of conduction, and thus reflects axonal function and integrity. It is now possible to estimate an “aggregate” g-ratio in vivo using MRI. The aim of this study was to assess the variation of the MRI-derived fiber g-ratio in the brain of healthy individuals, and to characterize its variation across the lifespan. Thirty-eight healthy participants, aged between 20 and 76, were recruited. Whole-brain g-ratio maps were computed and analyzed voxel-wise. Median tract g-ratio values were also extracted. No significant effect of gender was found, whereas age was found to be significantly associated with the g-ratio within the white matter. The tract-specific analysis showed this relationship to follow a nearly-linear increase, although the slope appears to slow down slightly after the 6th decade of life. The most likely interpretation is a subtle but consistent reduction in myelin throughout adulthood, with the density of axons beginning to decrease between the 4th and 5th decade.
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