University of Texas at Dallas, School of Behavioral and Brain Sciences, USA.
University of Texas at Dallas, School of Behavioral and Brain Sciences, USA.
Neuroimage. 2019 Mar;188:198-207. doi: 10.1016/j.neuroimage.2018.12.012. Epub 2018 Dec 6.
Functional magnetic resonance imaging (fMRI) has been used to infer age-differences in neural activity from the hemodynamic response function (HRF) that characterizes the blood-oxygen-level-dependent (BOLD) signal over time. BOLD literature in healthy aging lacks consensus in age-related HRF changes, the nature of those changes, and their implications for measurement of age differences in brain function. Between-study discrepancies could be due to small sample sizes, analysis techniques, and/or physiologic mechanisms. We hypothesize that, with large sample sizes and minimal analysis assumptions, age-related changes in HRF parameters could reflect alterations in one or more components of the neural-vascular coupling system. To assess HRF changes in healthy aging, we analyzed the large population-derived dataset from the Cambridge Center for Aging and Neuroscience (CamCAN) study (Shafto et al., 2014). During scanning, 74 younger (18-30 years of age) and 173 older participants (54-74 years of age) viewed two checkerboards to the left and right of a central fixation point, simultaneously heard a binaural tone, and responded via right index finger button-press. To assess differences in the shape of the HRF between younger and older groups, HRFs were estimated using FMRIB's Linear Optimal Basis Sets (FLOBS) to minimize a priori shape assumptions. Group mean HRFs were different between younger and older groups in auditory, visual, and motor cortices. Specifically, we observed increased time-to-peak and decreased peak amplitude in older compared to younger adults in auditory, visual, and motor cortices. Changes in the shape and timing of the HRF in healthy aging, in the absence of performance differences, support our hypothesis of age-related changes in the neural-vascular coupling system beyond neural activity alone. More precise interpretations of HRF age-differences can be formulated once these physiologic factors are disentangled and measured separately.
功能磁共振成像（fMRI）已被用于从随时间变化的血氧水平依赖（BOLD）信号的血流动力学响应函数（HRF）推断神经活动的年龄差异。在健康老龄化的 BOLD 文献中，与年龄相关的 HRF 变化、这些变化的性质及其对大脑功能年龄差异测量的影响缺乏共识。研究间的差异可能是由于样本量小、分析技术和/或生理机制所致。我们假设，通过大样本量和最小的分析假设，HRF 参数的年龄相关变化可能反映了神经血管耦联系统的一个或多个组成部分的改变。为了评估健康老龄化中的 HRF 变化，我们分析了来自剑桥老龄化与神经科学中心（CamCAN）研究的大型人群数据集（Shafto 等人，2014 年）。在扫描过程中，74 名年轻（18-30 岁）和 173 名年长（54-74 岁）参与者观看了位于中央注视点左右两侧的两个棋盘，同时听到双耳声音，并通过右食指按钮按下进行响应。为了评估年轻组和年长组之间 HRF 形状的差异，使用 FMRIB 的线性最优基集（FLOBS）估计 HRF，以最小化先验形状假设。听觉、视觉和运动皮质中，年轻组和年长组之间的 HRF 存在差异。具体而言，我们观察到与年轻成年人相比，年长成年人的听觉、视觉和运动皮质中的峰值时间延长和峰值幅度降低。健康老龄化中 HRF 形状和时间的变化，在没有表现差异的情况下，支持我们关于神经血管耦联系统与单独的神经活动相关的年龄变化的假设。一旦这些生理因素被分离并分别测量，就可以对 HRF 的年龄差异进行更精确的解释。
