Department of Radiology, University of California San Diego, 9500 Gilman Drive, MC 0677, La Jolla, CA 92093-0677, USA.
Philos Trans R Soc Lond B Biol Sci. 2021 Jan 4;376(1815):20190624. doi: 10.1098/rstb.2019.0624. Epub 2020 Nov 16.
Several current functional neuroimaging methods are sensitive to cerebral metabolism and cerebral blood flow (CBF) rather than the underlying neural activity itself. Empirically, the connections between metabolism, flow and neural activity are complex and somewhat counterintuitive: CBF and glycolysis increase more than seems to be needed to provide oxygen and pyruvate for oxidative metabolism, and the oxygen extraction fraction is relatively low in the brain and when oxygen metabolism increases. This work lays a foundation for the idea that this unexpected pattern of physiological changes is consistent with basic thermodynamic considerations related to metabolism. In the context of this thermodynamic framework, the apparent mismatches in metabolic rates and CBF are related to preserving the entropy change of oxidative metabolism, specifically the O/CO ratio in the mitochondria. However, the mechanism supporting this CBF response is likely not owing to feedback from a hypothetical O sensor in tissue, but rather is consistent with feed-forward control by signals from both excitatory and inhibitory neural activity. Quantitative predictions of the thermodynamic framework, based on models of O and CO transport and possible neural drivers of CBF control, are in good agreement with a wide range of experimental data, including responses to neural activation, hypercapnia, hypoxia and high-altitude acclimatization. This article is part of the theme issue 'Key relationships between non-invasive functional neuroimaging and the underlying neuronal activity'.
目前有几种功能性神经影像学方法可以检测脑代谢和脑血流（CBF），而不是潜在的神经活动本身。从经验上看，代谢、血流和神经活动之间的联系非常复杂，而且有些违背直觉：CBF 和糖酵解的增加似乎超过了为氧化代谢提供氧气和丙酮酸所需的量，而大脑中的氧提取分数相对较低，当氧气代谢增加时也是如此。这项工作为以下观点奠定了基础，即这种出乎意料的生理变化模式与与代谢相关的基本热力学考虑是一致的。在这个热力学框架下，代谢率和 CBF 的明显不匹配与保持氧化代谢熵变有关，具体来说与线粒体中的 O/CO 比值有关。然而，支持这种 CBF 反应的机制可能不是由于组织中假设的 O 传感器的反馈，而是与来自兴奋性和抑制性神经活动的信号的前馈控制一致。基于 O 和 CO 运输模型以及可能的 CBF 控制神经驱动因素的热力学框架的定量预测，与广泛的实验数据非常吻合，包括对神经激活、高碳酸血症、缺氧和高原适应的反应。本文是主题为“非侵入性功能神经影像学与潜在神经元活动之间的关键关系”的一部分。
