视觉逃避行为的抉择神经环路机制研究

Decision-making is a key component of cognition and involved in diverse processes ranging from the extraction of the salient sensory information to performance of appropriate behaviors. Although decision-making-related neurons are found in some brain areas, the neural circuitry mechanism underlying decision-making remains largely unknown, asking for systematic examination at a whole-brain scale. Larval zebrafish possesses a conserved vertebrate brain architecture, a rich repertoire of behaviors, and a small transparent brain amenable to abundant techniques for in vivo studies. Larval zebrafish is becoming an ideal model for dissecting the neural circuits underlying brain functions Here I propose to elucidate the neural circuit underlying decision-making across the whole brain, by using the visually evoked escape behavior of larval zebrafish as a model. The activities of all the neurons in the brain of awake larval zebrafish will be simultaneously monitored together with escape behavior. How decision is made among such whole-brain neuronal activities will be deciphered by identifying the crucial neural circuit in decision-making, through large-data analysis such as image processing, dimension reduction and regression. Neurons of important types will be examined for their roles in decision-making by combining transgenic fish lines. Finally the activity of the identified neural circuit will be manipulated specifically through optogenetic approaches for examining its causal role in decision-making. With all these work, this project will improve our understanding of neural circuit mechanisms underlying decision-making at a whole-brain scale.

抉择是认知过程的重要组成部分，从提取显著的感觉信息到行使恰当的行为都涉及到抉择。前人工作已经在多个脑区发现了与抉择相关的神经元，但抉择的神经环路机制尚不清楚，有待在全脑范围内进行系统研究。幼年斑马鱼具有脊椎动物保守的神经系统结构和丰富的行为，其小而透明的大脑便于结合多种在体研究方法，是在神经环路水平上研究脑功能的理想模式动物。本项目拟利用视觉诱发的斑马鱼逃避行为为模型，在全脑尺度上研究抉择的神经环路机制。首先应用光片照明荧光成像技术，在清醒斑马鱼标本上，实时记录抉择过程中全脑数十万个神经元的活动，并同时观察动物行为；通过图像处理、降维、回归等分析手段，解析全脑神经元活动对抉择的编码，确定抉择中关键的神经环路；结合转基因方法，考察不同类型神经元在抉择过程中的活动；进而，通过光遗传学操纵特定神经元集群的活动，确定特定神经环路在抉择中的作用。本研究将在全脑尺度上深化对抉择神经环路机制的认识。

抉择是认知过程的重要部分，此前在多个脑区都发现了与抉择相关的神经元活动，但全脑范围的神经环路如何做出抉择，特别是面对不完全感觉信息时的自主抉择，尚不清楚。本项目以视觉诱发的概率性逃避行为作为模型，结合幼年斑马鱼和光片照明显微镜在神经功能快速成像中的优势，记录到了抉择过程中的全脑神经元活动。有监督的主成分分析结果表明，在视觉刺激前2秒内的神经元活动已经可以预测动物是否逃避。进一步逐个分析这段时间内的神经元活动，发现有较多的后脑神经元在不逃避的决定之前活动偏高，显示它们的群体活动代表了动物对外界刺激的敏感状态。为了厘清这些神经元在上下游环路中的位置和因果性作用，我们建立了特异标记伽马-氨基丁酸能抑制性神经元、多巴胺能神经元等的转基因斑马鱼品系，能够光学调控任意神经元集群活动同时观察全脑神经元与动物行为响应的实验系统，以及能够直接观察神经元电压活动以及胞外钾离子浓度的纳米电压探针，并且正在开发根据神经元活动模式实时编辑感觉与光遗传学调控的闭环系统。这些工具与前述发现相结合，将能够通过通过实时精细调控破解和模拟动物自主抉择的神经环路机制。

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