Diffusion MRI is a powerful tool for imaging brain structure, but it is challenging to discern the biological underpinnings of plasticity inferred from these and other non-invasive MR measurements. Biophysical modeling of the diffusion signal aims to render a more biologically rich image of tissue microstructure, but the application of these models comes with important caveats. A separate approach for gaining biological specificity has been to seek converging evidence from multi-modal datasets. Here we use metrics derived from diffusion kurtosis imaging (DKI) and the white matter tract integrity (WMTI) model along with quantitative MRI measurements of T1 relaxation to characterize changes throughout the white matter during an 8-week, intensive reading intervention (160 total hours of instruction). Behavioral measures, multi-shell diffusion MRI data, and quantitative T1 data were collected at regular intervals during the intervention in a group of 33 children with reading difficulties (7-12 years old), and over the same period in an age-matched non-intervention control group. Throughout the white matter, mean ‘extra-axonal’ diffusivity was inversely related to intervention time. In contrast, model estimated axonal water fraction (AWF), overall diffusion kurtosis, and T1 relaxation time showed no significant change over the intervention period. Both diffusion and quantitative T1 based metrics were correlated with pre-intervention reading performance, albeit with distinct anatomical distributions. These results are consistent with the view that rapid changes in diffusion properties reflect phenomena other than widespread changes in myelin density. We discuss this result in light of recent work highlighting non-axonal factors in experience-dependent plasticity and learning.

中文翻译：

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精读教学中快速白质可塑性的神经生物学基础

扩散 MRI 是一种强大的大脑结构成像工具，但从这些和其他非侵入性 MR 测量中推断出可塑性的生物学基础是具有挑战性的。扩散信号的生物物理建模旨在呈现组织微观结构的生物学更丰富的图像，但这些模型的应用伴随着重要的警告。获得生物学特异性的另一种方法是从多模态数据集中寻找聚合证据。在这里，我们使用来自扩散峰态成像 (DKI) 和白质束完整性 (WMTI) 模型的指标以及 T1 弛豫的定量 MRI 测量来表征在为期 8 周的强化阅读干预（总共 160 小时）期间整个白质的变化指令）。行为措施，33 名阅读困难儿童（7-12 岁）在干预期间定期收集多壳层扩散 MRI 数据和定量 T1 数据，同时在年龄匹配的非干预对照中收集团体。在整个白质中，平均“轴突外”扩散率与干预时间成反比。相比之下，模型估计的轴突水分数 (AWF)、整体扩散峰度和 T1 弛豫时间在干预期间没有显着变化。尽管具有不同的解剖分布，但基于扩散和定量 T1 的指标都与干预前的阅读表现相关。这些结果与扩散特性的快速变化反映了髓鞘密度广泛变化以外的现象的观点一致。