Our brains are a dense tangle of billions of nerve cells connected together at synapses. Knowing how everything links up is key to understanding how the brain works -- but it's a huge challenge. Figuring out the brain's wiring diagram is the aim of 'connectomics'. It's done at many scales: from the 'super highways' linking brain areas down to individual cells and their connections. This video shows how, for the first time, scientists have reconstructed the wiring of tiny pieces of the mouse brain and related it to the function of individual cells.