If this looks like an incredibly complex wiring diagram to you, it's because it kinda is: you're looking at the Allen Mouse Brain Connectivity Atlas, the first detailed map of any mammal's neural network.
It's not a full connectome -- the name given to maps of every single interconnection between neurons in a brain -- but it's the most detailed rendering of interconnections in any mammalian brain yet. It traces connections between tiny cubes, called voxels, of brain tissue containing between 100 and 500 neurons. New Scientist describes how it was made:
Hongkui Zeng and colleagues at the Allen Institute for Brain Science in Seattle, Washington, injected the brains of 469 mice with a virus that introduced a fluorescent protein into the neural network... Because each animal was injected at a slightly different location, when taken together, the fluorescing proteins gave a snapshot of the network's shape. Next, the team diced up each brain into 500,000 pieces each measuring 100 micrometers cubed. Based on the strength of fluorescence in the cubes, they generated a 3D map of how each of the 469 different signals spread through the brain's thoroughfares and quieter byroads.
Sadly, the researchers admit that it will be years before a similar map of the human brain is made. But in the meantime, the result, published in Nature, is a data set that will be used decades to come -- providing an essential stepping stone to better understanding conditions like schizophrenia and Alzheimer's. [Nature via New Scientist]