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

了解大脑中的电信号模式如何引起复杂的行为-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理和运动障碍也是至关重要的。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，具有长距离的相互作用，在非常短(毫秒)和非常长(年)的时间尺度上变化。该奖学金的总体目标是开发一种工具，可以在足够的规模和分辨率下与大脑动态交互，从而对神经电路进行反向工程。就像自动驾驶汽车如何通过与世界动态互动(加速、制动、成像)来建立世界模型(例如，其他汽车、道路几何形状、路面)；这里提出的系统将动态询问神经元群体-以细胞级别的分辨率和与个人动作电位相当的时间动力学--生成关键神经过程的模型，并对神经电路进行反向工程。这样的系统不仅对我们对神经表征等基本过程的理解具有根本性的影响，还可以用来“驱动”神经元电路，这将使脑机接口在神经精神病学假肢和临床应用(如癫痫预防)方面取得新的前沿。电生理学技术是询问来自单个神经元的电信号的黄金标准。然而，这些需要将巨大的电子探测器插入大脑，使其无法接触到大量神经元。取而代之的是，我将使用一种完全不同的方式来研究神经元电路：光。自然界为我们提供了光敏蛋白质，这些蛋白质可以光学地报告随着荧光的变化而发生的电学变化，或者在光激发下产生电信号。通过将这些蛋白质改造成神经元，就有可能光学读出并控制大脑中的电活动。这项研究将完善一种名为“电压指示器”的新型报告系统，它可以直接报告动作电位，而不是反映电压变化的指标，比如钙离子的变化。钙离子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会丢失。相比之下，电压指示器实时观察动作电位，这对于与大脑动态交互至关重要-带有摄像头延迟的自动驾驶汽车很快就会撞车！为了跟上这些快速变化的步伐，我将开发超快的光学硬件，在动作电位传播的时间内读取和控制电信号，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环路，将有可能触发神经元产生尖峰，然后‘跟踪’做出反应的神经元，从而确定接线图。这种全光学的方法可以在体内实现高通量的细胞分辨率连接(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障碍中的电路缺陷。该奖学金由伦敦大学学院沃尔夫森生物医学研究所主办，建立了一些工具来提出关于大脑功能和结构的全新问题，这是现有技术无法实现的。它将在神经科学和其他领域(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BBSRC优先领域“促进健康的生物科学”在“促进生物科学的技术发展”响应模式优先事项下非常契合。

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.