Ultrastructural visualisation of synaptic function in brains of behaving mice

大脑的基本功能是处理信息以触发行动：接收感官输入，并将其与先前的经验相结合，以产生适当的反应。信息以微小的电活动信号的形式进行编码，这些信号在连接在一起形成电路的专门细胞(神经元)之间传递。为了理解神经元如何计算它们的反应--大脑工作的本质--我们需要知道两件关键的事情：(1)神经元是如何连接在一起的(“连接模式”)，以及(2)当动物进行行为时，在被称为突触的特殊神经元连接点上发生了什么信号。理解这两个要素是至关重要的：识别“谁在和谁说话”，也要识别哪些突触是活跃的，它们有多强--以便了解大脑是如何工作的。在研究哺乳动物大脑中庞大且相互关联的网络时，解决这些问题是一个重大挑战。这严重限制了我们对大脑运作的理解。最近，研究人员找到了一种方法来解决使用一种特殊类型的电子显微镜来识别神经元之间的突触连接的问题，这种电子显微镜允许以三维细节重建目标大脑区域，精度达到纳米级，这种方法被称为3D-EM。当与强大的计算分析方法相结合时，就有可能绘制出电路中的神经元连接，从而显示出接线图。然而，仍然缺乏的是突触的功能信息-它们的强度和激活模式-对于全面理解电路运行是必不可少的。这个项目的目的是通过开发最先进的方法来并行解决问题(1)和(2)，为我们提供一种革命性的新方法来使用3D-EM读出突触的活动和强度。我们将在计划的工作中应用我们的方法，首次生成突触活动的功能图，覆盖在动物处理感觉(视觉)输入和执行复杂行为的同一电路的接线图上。在我们的试点实验中，我们已经证明，我们的技术可以用于可靠地识别突触并估计它们的强度。我们将优化这一策略，并将其与强大的新机器学习技术相结合，用于基于计算机的图像分析，这将作为研究计划的一部分开发。这将使我们能够对3D脑组织体积中的数万个结构进行自动化分析，速度要快得多，产生的准确性和重复性也比专家人类所能实现的要好得多。这些开创性的新方法应该会让我们对单个突触的功能和行为之间的关系有基本的洞察--这是系统神经科学领域的圣杯。在未来，我们独特的方法也可能被用来检查神经退行性疾病中发生的信息信号障碍，为治疗提供潜在的靶点。这些发现和主题与BBSRC当前的倡议非常一致，包括研究和创新优先事项--“推进生物科学发现的前沿”，其中包括作为其两个主要目标的“理解生命规则”和“变革性技术”。我们的核心目标也与BBSRC响应模式优先事项“数据驱动的生物学”、“生物科学的技术发展”和“生物科学的系统方法”直接相关。

The basic function of the brain is to process information to trigger action: receiving sensory input and integrating it with prior experience to generate appropriate responses. The information is encoded in the form of small electrical activity signals that are passed between specialized cells (neurons) wired up together to form circuits. To understand how neurons are able to compute their responses - the essence of a working brain - we need to know two key things: (1) how neurons are connected together (the 'wiring pattern'), and (2) what signals are occurring at the specialized neuronal connection points, called synapses, as an animal carries out behaviours. It is essential to understand both elements: identify "who is talking to who", and also identify which synapses are active and how strong they are - in order to understand how the brain works. When examining the large and richly interconnected networks in mammalian brains, solving these problems is a major challenge. This has severely limited our understanding of brain operation. Recently, researchers have found a way to address the problem of identifying synaptic connections between neurons using a special type of electron microscope which allows a target brain region to be reconstructed in three-dimensional detail down to nanometre resolution, an approach called 3D-EM. When combined with powerful computational analysis approaches, it then becomes possible to map out the neuronal connections in a circuit and therefore reveal the wiring diagram. What is still missing, however is the functional information at the synapses - their strength and pattern of activation - that is essential for a full understanding of circuit operation.The aim of this project is to address problems (1) and (2) in parallel by developing state-of-the-art approaches to provide us with a revolutionary new way to read out synaptic activity and strength using 3D-EM. We will apply our methods in the planned work to generate, for the first time, functional maps of synaptic activity overlaid onto the wiring diagram of the same circuit as an animal processes sensory (visual) inputs and performs complex behaviours. In our pilot experiments we have already shown that our technique can be used to reliably identify synapses and estimate their strength. We will optimise this strategy and combine it with powerful new machine-learning technologies for computer-based image analysis which will be developed as part of the research program. This will permit an automated analysis of tens of thousands of structures in a 3D brain tissue volume that is both much faster and yields better accuracy and reproducibility than is achievable by expert humans.These ground-breaking new methodologies should give us fundamental insights into the relationship between the function of individual synapses and behaviour - a holy grail in the field of systems neuroscience. In the future, our unique methodology may also be used to examine the disorders in information signalling that occur in neurodegenerative diseases, offering potential targets for therapeutics. The findings and the topic are very well-aligned with current BBSRC initiatives including the Research and Innovation Priority, 'Advancing the frontiers of bioscience discovery', which includes 'Understanding the rules of life' and 'Transformative technologies' as two of its principal aims. Our core objectives are also directly relevant to the BBSRC responsive mode priorities 'Data-driven biology', 'Technology development for the biosciences' and 'Systems approaches to the biosciences'.