Each nerve cell in mammalian brains communicates with about a thousand other nerve cells. This creates a communication network that is likely one of the most complex networks that we know of. Understanding the rules by which this network is created and by which it operates is one of the current questions in neuroscience. MORITZ HELMSTAEDTER studies this connectivity and he is particularly interested in how the cerebral cortex is wired up in mammalian brains. As he explains in this video, the researchers use highly advanced electron microscopy to create a three-dimensional image dataset from which they reconstruct the network structure of the brain. They found, in contrast to popular opinion, that the wiring in the cerebral cortex of mammals is not random but that neurons decide whom to contact and which neurons should go when. That the mammalian cortex has this level of precision is an important insight for further studies and could be helpful in the study of psychiatric diseases.