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The MICrONS Project published package of papers about an unprecedented dataset of high resolution anatomical images of individual cells in mouse visual cortex, mapped on to their responses.

This integrated view of function and structure lays a foundation for discovering the computational bases of cortical circuits. A cubic millimetre might not sound like much — roughly the size of a grain of sand — but to neuroscientists, it is enormous. One cubic millimetre of a mammalian brain contains tens of thousands of neurons with hundreds of millions of connections, or synapses, between them. For most of the history of neuroscience, tracing the detailed connectivity (or connectomics) and measuring activity of neurons at such a large scale was unthinkable. Instead, neuroscientists worked at more manageable scales — even single pairs of connected cells can provide important information, especially when accrued over hundreds of labs doing similar experiments. Nevertheless, the goal of studying millimetre-scale volumes of brain in such detail started to come closer after a period of intense focus on new neuroscience technologies in the 1990s and 2000s. This period led to tools to label, trace and image the activity of neurons in increasingly large populations. However, the fundamental problem of scale remained. A complete reconstruction of a cubic millimetre of neurons requires roughly a petabyte of data. Tracing the intricate branches of the neurons is far too time consuming to do by hand, so improved tools for automation were needed. A parallel revolution in computing — increased computing power and advances in machine learning and artificial intelligence — suddenly made those challenges tractable. This brings us to today’s announcement of the MICrONS project. The team made and designed tools to allow dense neural reconstruction at scale. The resulting data set includes 200,000 cells and 523 million connections in the primary visual cortex and surrounding areas of a mouse. A unique contribution of the MICrONS project is that it also includes in vivo functional data from around 75,000 of the neurons. Even landmark connectomics studies, such as FlyWire, include only the anatomical data. The inclusion of functional data means that we can directly relate connectivity to function and decipher the elusive algorithms of the cortex.