Behzadi Yashar, Liu Thomas T
Center for Functional Magnetic Resonance Imaging and Department of Radiology, University of California-San Diego, 9500 Gilman Drive, La Jolla, MC 0677, CA 92093-0677, USA.
Neuroimage. 2006 Aug 1;32(1):9-15. doi: 10.1016/j.neuroimage.2006.03.005. Epub 2006 Apr 25.
Localized changes in oxygen consumption related to increased neural activity can result in a small and transient "initial dip" of the blood oxygenation level-dependent (BOLD) signal used in functional magnetic resonance imaging (fMRI). The initial dip has been of great interest to the fMRI community because it may provide a more accurate and localized measure of neural activity than the conventional BOLD signal increase. Although potentially useful as a technique for human brain mapping, the initial dip is not always detected and has been a source of some controversy. In this study, the BOLD response to a 4-s long visual stimulus was measured with a 3-T MRI system in 5 healthy volunteers both before and immediately after a 200-mg oral caffeine dose. The caffeine dose significantly (P < 0.001) reduced or eliminated the initial dip in all subjects. These findings suggest that caffeine usage may be a key factor in the detection of the initial dip in human fMRI studies.
与神经活动增加相关的局部氧消耗变化可导致功能磁共振成像（fMRI）中使用的血氧水平依赖（BOLD）信号出现小而短暂的“初始下降”。初始下降一直是fMRI领域非常感兴趣的内容，因为它可能比传统的BOLD信号增加提供更准确和局部的神经活动测量。尽管作为一种人类脑图谱技术可能有用，但初始下降并非总能被检测到，并且一直是一些争议的来源。在本研究中，使用3-T MRI系统在5名健康志愿者口服200毫克咖啡因剂量之前和之后立即测量了对4秒长视觉刺激的BOLD反应。咖啡因剂量在所有受试者中均显著（P < 0.001）减少或消除了初始下降。这些发现表明，在人类fMRI研究中，咖啡因的使用可能是检测初始下降的关键因素。
