Integration of functional and structural knowledge across scales to decipher information processing in the mammalian brain

哺乳动物的大脑是人类已知的最复杂的结构之一。这种复杂性在很大程度上源于大脑在过多的时间和长度尺度上运行的事实：神经元的长度为毫米，但神经元之间的连接是纳米级的。了解信息如何在这个复杂的结构中处理是理解精神疾病等功能障碍以及构建先进的“人工智能”的关键先决条件。然而，只有当神经元的活动能够与为神经元计算提供基底的神经元网络的结构相联系时，才能实现这一点。在过去的几十年里，人们在使用电子显微镜来破译神经回路的逻辑方面取得了惊人的进展。然而，电子显微镜是耗时的，并且由于电子不会渗透到组织中超过几纳米，因此在电子成像之前或期间必须将脑组织切成薄片。到目前为止，这将电子显微镜限制在相对较小的组织体积，长度高达几个100 μ m的立方体。另一方面，X射线可以穿透组织很长的距离（毫米甚至厘米）。同步加速器产生最强大的X射线，同步加速器技术正在进行革命，以进一步提高功率-光子数量以及X射线束的质量（相干性）-许多数量级。ESRF同步加速器（英国是其成员国）是第一个获得这种升级的高能同步加速器。在这个项目中，我们建议充分利用这种新的X射线技术，并进一步发展X射线断层扫描，能够在不切割的情况下获得三维图像，使我们能够从大块（几立方毫米）脑组织中解析精细的神经元结构。我们将联合收割机结合这种新的X射线断层扫描与以前的功能成像在活的老鼠，以联系神经活动的神经结构。随后，我们将对部分组织进行高分辨率电子显微镜检查，以结合联合收割机对神经元之间突触接触的详细识别以及来自X射线成像的关于神经元身份和神经元过程的大规模信息。我们将首先应用这种新方法来了解信息是如何在最突出的大脑区域--小鼠嗅球中转化的，该区域处理来自鼻子的信息，并将其传递给大脑的其他部分。由于同步加速器X射线成像的高通量，我们将能够直接比较不同个体之间相同的基因标记电路。这将使我们能够回答长期存在的问题，两种哺乳动物的大脑有多不同或相似。最后，结合上述所有技术--功能成像、同步辐射X射线成像和电子显微镜--我们能够描述嗅球神经元网络如何处理信息的逻辑，从而开发出一种新的工具来理解神经回路如何处理信息。然而，在生物组织中建立同步加速器X射线成像以及功能成像和电子显微镜将具有更广泛的潜力，成为了解整个组织（肺，肝，胸腺）中细胞和亚细胞结构（病毒，癌症微环境，免疫小生境）的特性的多功能工具。因此，通过开发这种联合方法，我们不仅可以解决直接的神经科学问题，而且还可以开发一种新的生命科学物理科学方法，并在这两个专业中培养一批同等的研究人员。

The mammalian brain is one of the most complex structures known to mankind. A lot of this complexity stems from the fact that brains operate on a plethora of time and length scales: neurons stretch for millimetres, yet the connections between neurons are of nanometre scale. Understanding how information is processed in this complex structure is a critical prerequisite for understanding dysfunction such as psychiatric disease as well as for building advanced "artificial intelligences". This, however, can only be achieved if the activity of neurons can be linked to the structure of the network of neurons that provides the substrate for neuronal computation. The last decades have seen astonishing progress in using electron microscopy to decipher the logic of neural circuits. Electron microscopy, however, is time-consuming and as electrons do not permeate into tissue for more than a few nanometres, brain tissue has to be cut into thin sections before or during electron imaging. This has so far limited electron microscopy to relatively small tissue volumes, cubes with up to few 100 um length. X-rays, on the other hand, can penetrate tissue for long distances (millimetres or even centimetres). Synchrotrons produce the most powerful X-rays and there is an ongoing revolution in synchrotron technology to further increase the power - the number of photons as well as the quality (coherence) of the X-ray beams - by many orders of magnitude. The ESRF synchrotron (where the UK is a member country) is the first high-energy synchrotron to have received such upgrade. In this project we propose to fully make use of this new X-ray technology and further develop X-ray tomography, the ability to obtain 3-dimensional images without cutting, to allow us to resolve fine neuronal structures from large (several cubic millimetre) pieces of brain tissue. We will combine this new X-ray tomography with prior functional imaging in living mice in order to link the neural activity to the neural structure. We will subsequently perform high resolution electron microscopy on parts of the tissue to combine detailed identification of synaptic contacts between neurons with large-scale information about neuron identity and neuronal processes from X-ray imaging. We will initially apply this new approach to understand how information is transformed in a most prominent brain region, the mouse olfactory bulb, that processes information from the nose for the rest of the brain. Due to the high throughput of synchrotron X-ray imaging we will be able to directly compare the same, genetically labelled, circuits between different individuals. This will allow us to answer the long-standing question how different or alike two mammalian brains are. Finally, combining all of the above - functional imaging, synchrotron X-ray imaging and electron microscopy - enables us to describe the logic of how information is processed by the network of neurons in the olfactory bulb.Altogether, we will develop a new tool to understand how neural circuits process information. Establishing synchrotron X-ray imaging together with functional imaging and electron microscopy in biological tissue will, however, have even wider potential to become a versatile tool to understand the properties of cells and subcellular structure (viruses, cancer microenvironments, immune niches) in the context of entire tissues (lung, liver, thymus). Thus, by developing this joint approach we will not only solve immediate neuroscience questions but also develop a new physical science approach to life science and grow a group of researchers equally at home in both specialties.