Handwerker Daniel A, Gazzaley Adam, Inglis Ben A, D'Esposito Mark
Henry H. Wheeler Jr. Brain Imaging Center, Helen Wills Neuroscience Institute, University of California, Berkeley, USA.
Hum Brain Mapp. 2007 Sep;28(9):846-59. doi: 10.1002/hbm.20307.
The magnitude and shape of blood oxygen level-dependent (BOLD) responses in functional MRI (fMRI) studies vary across brain regions, subjects, and populations. This variability may be secondary to neural activity or vasculature differences, thus complicating interpretations of BOLD signal changes in fMRI experiments. We compare the BOLD responses to neural activity and a vascular challenge and test a method to dissociate these influences in 26 younger subjects (ages 18-36) and 24 older subjects (ages 51-78). Each subject performed a visuomotor saccade task (a vascular response to neural activity) and a breathholding task (vascular dilation induced by hypercapnia) during separate runs in the same scanning session. For the saccade task, signal magnitude showed a significant decrease with aging in FEF, SEF, and V1, and a delayed time-to-peak with aging in V1. The signal magnitudes from the saccade and hypercapnia tasks showed significant linear regressions within subjects and across individuals and populations. These two tasks had weaker, but sometimes significant linear regressions for time-to-peak and coherence phase measures. The significant magnitude decrease with aging in V1 remained after dividing the saccade task magnitude by the hypercapnia task magnitude, implying that the signal decrease is neural in origin. These findings may lead to a method to identify vascular reactivity-induced differences in the BOLD response across populations and the development of methods to account for the influence of these vasculature differences in a simple, noninvasive manner.
在功能磁共振成像（fMRI）研究中，血氧水平依赖（BOLD）反应的大小和形状在不同脑区、受试者和人群中存在差异。这种变异性可能继发于神经活动或血管系统差异，从而使fMRI实验中BOLD信号变化的解释变得复杂。我们比较了BOLD对神经活动和血管挑战的反应，并测试了一种方法，以区分26名年轻受试者（18 - 36岁）和24名年长受试者（51 - 78岁）中的这些影响。在同一扫描 session 的不同运行中，每个受试者执行了视觉运动扫视任务（对神经活动的血管反应）和屏气任务（高碳酸血症引起的血管扩张）。对于扫视任务，信号大小在额眼区（FEF）、补充眼区（SEF）和初级视觉皮层（V1）中随年龄增长显著下降，并且在V1中随年龄增长峰值时间延迟。扫视任务和高碳酸血症任务的信号大小在受试者内部以及个体和人群之间显示出显著的线性回归。对于峰值时间和相干相位测量，这两个任务的线性回归较弱，但有时也很显著。在将扫视任务大小除以高碳酸血症任务大小后，V1中随年龄增长的显著大小下降仍然存在，这意味着信号下降起源于神经。这些发现可能会导致一种方法，用于识别不同人群中血管反应性引起的BOLD反应差异，并开发以简单、无创方式考虑这些血管系统差异影响的方法。
