Xu Feng, Liu Peiying, Pekar James J, Lu Hanzhang
Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390, USA; The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University, 601 North Caroline Street, MD 21287, USA; F. M Kirby Center for Functional Brain Imaging, Kennedy Krieger Institute, 707 N Broadway, Baltimore, MD 21205, USA.
Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390, USA; The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University, 601 North Caroline Street, MD 21287, USA; Department of Psychiatry, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390, USA.
Neuroimage. 2015 Apr 15;110:39-47. doi: 10.1016/j.neuroimage.2015.01.046. Epub 2015 Jan 30.
Caffeine, as the most commonly used stimulant drug, improves vigilance and, in some cases, cognition. However, the exact effect of caffeine on brain activity has not been fully elucidated. Because caffeine has a pronounced vascular effect which is independent of any neural effects, many hemodynamics-based methods such as fMRI cannot be readily applied without a proper calibration. The scope of the present work is two-fold. In Study 1, we used a recently developed MRI technique to examine the time-dependent changes in whole-brain cerebral metabolic rate of oxygen (CMRO2) following the ingestion of 200mg caffeine. It was found that, despite a pronounced decrease in CBF (p<0.001), global CMRO2 did not change significantly. Instead, the oxygen extraction fraction (OEF) was significantly elevated (p=0.002) to fully compensate for the reduced blood supply. Using the whole-brain finding as a reference, we aim to investigate whether there are any regional differences in the brain's response to caffeine. Therefore, in Study 2, we examined regional heterogeneities in CBF changes following the same amount of caffeine ingestion. We found that posterior brain regions such as posterior cingulate cortex and superior temporal regions manifested a slower CBF reduction, whereas anterior brain regions including dorsolateral prefrontal cortex and medial frontal cortex showed a faster rate of decline. These findings have a few possible explanations. One is that caffeine may result in a region-dependent increase or decrease in brain activity, resulting in an unaltered average brain metabolic rate. The other is that caffeine's effect on vasculature may be region-specific. Plausibility of these explanations is discussed in the context of spatial distribution of the adenosine receptors.
咖啡因作为最常用的兴奋剂药物，可提高警觉性，在某些情况下还能改善认知能力。然而，咖啡因对大脑活动的确切影响尚未完全阐明。由于咖啡因具有明显的血管效应，且该效应独立于任何神经效应，因此在未进行适当校准的情况下，许多基于血液动力学的方法（如功能磁共振成像）无法轻易应用。本研究工作的范围有两个方面。在研究1中，我们使用一种最近开发的磁共振成像技术，来检测摄入200毫克咖啡因后全脑脑氧代谢率（CMRO2）随时间的变化。结果发现，尽管脑血流量（CBF）显著下降（p<0.001），但全脑CMRO2并没有显著变化。相反，氧摄取分数（OEF）显著升高（p=0.002），以充分补偿血液供应的减少。以全脑研究结果为参考，我们旨在研究大脑对咖啡因的反应是否存在区域差异。因此，在研究2中，我们检测了摄入等量咖啡因后CBF变化的区域异质性。我们发现，后扣带回皮层和颞上区等后脑区域的CBF下降较慢，而包括背外侧前额叶皮层和内侧额叶皮层在内的前脑区域的下降速度较快。这些发现有几种可能的解释。一种是咖啡因可能导致大脑活动在区域上出现增加或减少，从而使平均脑代谢率保持不变。另一种是咖啡因对血管系统的影响可能具有区域特异性。我们将在腺苷受体空间分布的背景下讨论这些解释的合理性。
