All-optical electrophysiology: probing real-time dynamics of neural circuits

了解大脑中的电信号模式如何产生复杂的行为-"神经代码“-不仅对于发现学习、决策和认知等基本过程的神经基础至关重要;而且对于治疗神经精神病和运动障碍也至关重要。挑战在于，与计算机不同，大脑中的神经元是高度重复的、非线性的，并且具有在非常短（毫秒）和非常长（年）的时间尺度上变化的长距离相互作用。该奖学金的总体目标是开发一种工具，可以以足够的规模和分辨率与大脑动态交互，以逆向工程神经回路。就像自动驾驶汽车构建世界模型一样（例如，其他汽车、道路几何形状、路面）通过与其动态地交互来进行（加速、制动、成像）;这里提出的系统将动态地询问神经元群体-以细胞水平的分辨率和与个体动作电位相当的时间动态-生成关键神经过程的模型，并对神经回路进行“逆向工程”。这样的系统不仅对我们理解神经表征等基本过程具有根本性的意义，而且还可以用于“驱动”神经元电路，这将使神经精神修复和临床应用（如癫痫预防）的脑机接口成为新的前沿。然而，这需要将庞大的电探针插入大脑，使得无法访问大量的神经元。相反，我将使用一种完全不同的方式来处理神经元回路：光。大自然已经为我们提供了光敏蛋白质，它们可以光学地报告具有荧光变化的电变化，或者在光激发下产生电信号。通过将这些蛋白质工程化到神经元中，可以光学读出和控制大脑中的电活动。这项研究将完善一种称为“电压指示器”的新型报告器，它直接报告动作电位，而不是电压变化的代理，如钙变化。钙的变化比典型的动作电位慢两个数量级，这意味着关键的时间信息丢失了。相比之下，电压指示器实时观察动作电位，这对于与大脑的动态交互至关重要--带有摄像头延迟的自动驾驶汽车会很快崩溃！为了跟上这些快速的动态，我将开发超快的光学硬件，以便在动作电位传播的时间内读出和控制电信号，并以足够的规模访问神经元电路。此外，通过关闭读出和控制之间的循环，将有可能触发神经元发放尖峰，然后“跟踪”响应的神经元，从而确定接线图。这种“全光学”方法能够实现高通量的细胞分辨率连接组学（即电路的功能连接映射），并将改变我们对神经系统结构的理解，例如用于识别神经精神疾病中的电路缺陷。该奖学金由伦敦大学学院沃尔夫森生物医学研究所主办，建立工具来提出关于大脑功能和结构的全新问题，这是使用现有技术无法实现的。它将在神经科学及其他领域（包括心脏、肾脏和肝脏生理学）有广泛的应用。因此，拟议的研究金与生物安全与资源中心“生物科学技术开发"响应模式优先事项下的”生物科学促进健康“优先领域非常一致。

Understanding how patterns of electrical signals within the brain give rise to complex behaviour --- the 'neural code' --- is critical for not only discovering the neural basis of fundamental processes such as learning, decision making and cognition; but also for treating neuropsychiatric pathologies and motor impairments. The challenge is that unlike a computer, the neurons in the brain are highly recurrent, nonlinear and have long range interactions that vary across very short (millisecond) and very long (years) times-scales. The overall aim of this fellowship is to develop a tool that can dynamically interact with the brain at sufficient scale and resolution to reverse-engineer the neural circuitry. Much like how self driving cars build a model of the world (e.g. other cars, road geometry, road surface) by dynamically interacting with it (accelerating, braking, imaging); the systems proposed here will dynamically interrogate populations of neurons --- at cellular-level resolution and with temporal dynamics comparable to individual action potentials --- to generate models of key neural processes and 'reverse engineer' the neural circuitry. Such a system would not only have radical implications for our understanding of basic processes such neural representation; but also could be used to 'drive' neuronal circuits, which would enable new frontiers in brain machine interfaces for neuropsychiatric prosthetics and clinical applications such as seizure prevention.The gold-standard for interrogating electrical signals from individual neurons are electrophysiology techniques. However these require bulky electrical probes to be inserted into the brain, making it impossible to access large populations of neurons. Instead, I will address neuronal circuits using an entirely different modality: light. Nature has provided us with light sensitive proteins that can either optically report electrical changes with variations in fluorescence or generate an electrical signal under optical excitation. By engineering these proteins into neurons, it is possible to optically readout and control electrical activity in the brain. This fellowship will perfect a new type of reporter called a 'voltage indicator' that directly reports action potentials rather than proxies for voltage change, such as calcium variations. Calcium changes happen two orders of magnitude slower than a typical action potential, meaning that critical timing information is lost. In contrast, voltage indicators observe action potentials in real-time, which is critical for dynamically interacting with the brain --- a self-driving car with a camera delay would quickly crash! To keep pace with these rapid dynamics, I will develop ultra-fast optical hardware to readout and control electrical signals all within the time it takes an action potential to propagate, and at sufficient scale to access neuronal circuits. Moreover, by closing the loop between readout and control, it will be possible to trigger a neuron to spike, then 'track' the neurons that respond, thus determining the wiring diagram. This 'all-optical' approach enables high-throughput cellular resolution connectomics (i.e. functional connection mapping of circuits) in vivo, and would be transformative to our understanding of the structure of the nervous system, e.g. for identifying circuit defects in neuropsychiatric disorders.This fellowship, hosted at the Wolfson Institute for Biomedical Research at UCL, builds tools to ask entirely new questions about the function and structure of the brain, which are not possible using existing technology. It would have wide ranging applications in neuroscience and beyond (including cardiac, renal, and hepatic physiology). The proposed fellowship is therefore very well aligned with the BBSRC priority area 'biosciences for health' under the 'technology development for the biosciences' responsive mode priority.