It’s rather weird: If you’ve ever seen a computer ribbon cable — a flat, 2D ribbon of wires stuck together, such as an IDE hard drive cable — the brain is basically just a huge collection of these ribbons, traveling parallel or perpendicular to each other. There are almost zero diagonals, nor single neurons that stray from the neuronal highways. The human brain is just one big grid of neurons — a lot like the streets of Manhattan, minus Broadway, and then projected into three dimensions.
This new imagery comes from a souped-up MRI scanner that uses diffusion spectrum imaging to detect the movement of water molecules within axons (the long connections made by neurons). The brain has always been very difficult to image because of the wrinkly nature of the cerebral cortex that surrounds the brain — but this new MRI scanner finally has the ability to peer through the folds. Members of the Human Connectome Project first analyzed monkey brains (pictured above) — which are very similar to human brains — and then used their findings to tweak the MRI scanner to improve its imaging of human brains (pictured below). A connectome is a complete map of the connections and pathways in a brain — basically, the neuronal version of your DNA genome.
Full story here at National Institutes of Health.