Functional relationship between neural, metabolic and hemodynamic responses

描述(由申请人提供)：拟议工作的目标是确定和表征由诱发神经活动引起的代谢和血流动力学反应的时空界限。为此，将使用一种表达光敏感蛋白Channelopilopilsin-2的基因增强的小鼠模型，通过调节直接传递到大脑表面的光刺激(光刺激)的直径和强度来控制神经元的活动。首先，将使用亚微米分辨率的双光子显微镜来确定引起血流反应的最小神经元活动。神经元活动的大小和强度将使用钙指示剂来表征。然后，将使用血管内荧光染料来测量毛细血管中血流速度和血管直径的相应变化。其次，这些发现的一致性和分辨率的影响将通过使用数十微米分辨率的更大尺度光学成像来测量功能性脑血流量、代谢和整体血流动力学反应来进行调查。具体地说，以下光学方法将分别用于测量血流、代谢和整体血流动力学对神经活动的响应：激光散斑成像、本征自发荧光成像和本征信号的光学成像。后者是血氧水平依赖的功能磁共振成像(BOLD FMRI)的直接模拟。作为这个项目的结果，代谢和血流动力学反应的时空极限将以无与伦比的分辨率被揭示出来。此外，还将获得足够的知识来阐明当前脑研究工具(如功能磁共振成像)的理论和实践需求，以检测在血流动力学反应中编码的活动，这些活动可能被认为是不可检测的。这项工作将对动物和人类的脑功能成像研究产生巨大影响，包括临床和基础科学研究。为了进行拟议的研究，我将接受大脑功能的双光子成像和互补光学成像方法以及神经活动的电生理记录方面的培训。地方和国家专家的独特组合将提供和监督必要的培训。这项提议对于实现我的最终职业目标至关重要，我的最终目标是实现一个独立而成功的研究计划，专注于成像正常和病理的大脑功能。 公共卫生相关性：神经活动引起的血液动力学反应是研究动物和人类大脑功能的主要手段。像功能磁共振成像这样的方法现在在基础科学、发育、认知和临床研究中是必不可少的，这些研究涉及正常和受损的大脑功能。这项提议将揭示基于血流动力学的方法成像和检测大脑功能的基本局限性。

DESCRIPTION (provided by applicant): The objective of the proposed work is to determine and characterize the spatio-temporal limits of the metabolic and hemodynamic responses that result from evoked neural activity. For this purpose a genetically enhanced mouse model expressing the light-sensitive protein Channelrhodopsin-2 will be used whereby the neuronal activity can be controlled through the modulation of the diameter and intensity of a light stimulus delivered directly onto the surface of the brain (photo-stimulus). First, the minimum neuronal activity that elicits a blood flow response will be determined using two-photon microscopy with sub-micrometer resolution. The size and strength of the neuronal activity will be characterized using a calcium indicator. Then, an intra-vascular fluorescent dye will be used to measure corresponding changes in blood velocity and vessel diameter in capillaries. Second, the consistency of these findings and the effect of resolution will be investigated by measuring the functional cerebral blood flow, metabolic and overall hemodynamic responses using larger- scale optical imaging with resolution of tens of micrometers. Specifically, the following optical methods will be used to measure blood flow, metabolic and overall hemodynamic responses to neural activity: laser speckle imaging, intrinsic auto-fluorescence imaging and optical imaging of intrinsic signal, respectively. The latter is a direct analog of blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI). As a result of this project, the spatio-temporal limits of the metabolic and hemodynamic responses will be uncovered with unparalleled resolution. In addition, sufficient knowledge will be obtained to elucidate the theoretical and practical requirements of current brain research tools like fMRI to detect activities encoded in the hemodynamic response that may be thought to be undetectable. This work will have a tremendous impact in brain imaging studies of function in animals and humans, including clinical and basic science research. To perform the proposed studies I will undergo training in two-photon imaging of brain function and complementary optical imaging methods, and in electrophysiological recording of neuronal activity. A unique combination of local and national experts will provide and oversee the necessary training. This proposal is vital in fulfilling my ultimate career goal of attaining an independent and successful research program that focuses on imaging normal and pathological brain function. PUBLIC HEALTH RELEVANCE: The hemodynamic response induced by neural activity is, and has been, the principal means of studying brain function in animals and humans. Methods like functional magnetic resonance imaging are now essential in basic science, developmental, cognitive and clinical studies of normal and impaired brain function. This proposal will reveal the fundamental limits of hemodynamic-based methods to image and detect brain function.