Functional relationship between neural, metabolic and hemodynamic responses

描述（由申请人提供）：拟定工作的目的是确定和表征诱发神经活动引起的代谢和血液动力学反应的时空限制。为此目的，将使用表达光敏蛋白质视紫红质-2的遗传增强的小鼠模型，由此可以通过调节直接递送到脑表面上的光刺激（光刺激）的直径和强度来控制神经元活性。首先，将使用具有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。将使用钙指示剂表征神经元活动的大小和强度。然后，将使用血管内荧光染料来测量毛细血管中血液速度和血管直径的相应变化。其次，将通过使用分辨率为数十微米的更大尺度光学成像测量功能性脑血流、代谢和总体血液动力学反应来研究这些发现的一致性和分辨率的影响。具体而言，将使用以下光学方法来测量对神经活动的血流、代谢和总体血液动力学响应：分别为激光散斑成像、固有自发荧光成像和固有信号的光学成像。后者是血氧水平依赖功能磁共振成像（BOLD fMRI）的直接模拟。该项目的结果是，代谢和血液动力学反应的时空限制将以无与伦比的分辨率被揭示。此外，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）的理论和实践要求，以检测可能被认为无法检测的血液动力学反应中编码的活动。这项工作将对动物和人类功能的脑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，我将接受脑功能双光子成像和互补光学成像方法的培训，以及神经元活动的电生理记录。当地和国家专家的独特组合将提供和监督必要的培训。这个提议对于实现我的最终职业目标至关重要，即实现一个独立而成功的研究计划，专注于成像正常和病理性脑功能。 公共卫生相关性：由神经活动引起的血流动力学反应是并且一直是研究动物和人类脑功能的主要手段。像功能性磁共振成像这样的方法现在在正常和受损脑功能的基础科学、发育、认知和临床研究中至关重要。这项提议将揭示基于血液动力学的方法在成像和检测大脑功能方面的基本局限性。

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.