The typical brain scan shows a muted gray rendering of the brain, easily distinguished by a series of convoluted folds. But according to Van Wedeen, an Associate Professor in Radiology at Harvard, that image is just a shadow of the real brain. A new technique called Diffusion spectrum imaging (DSI) uses magnetic resonance signals to track the movement of water molecules in the brain: water diffuses along the length of neural wires, called axons. Scientists can use these diffusion measurements to map the wires, creating a detailed map of the brain's connectivity.

The first image shows half the cerebral hemisphere of a macaque monkey. The blue bundle of fibers running horizontally across the middle of the image is called the cingulum bundle, described by Wedeen as "a multilane highway" that runs from the prefrontal cortex, which is involved in planning and higher cognitive function, to the parietal cortex, which is mainly involved in synthesizing sensory information. While it looks quite complicated, it represents only a fraction - about 10 to 20 percent - of the wiring in that part of the brain.

On the second image one can see some of the owl monkey brain's anatomical structures. The treelike shape at lower left, for example, shows the longitudinal fibers of the cerebellum, a brain area that plays an important role in coordination and motor control, as well as in the integration of information from different senses. It's important to point out that even if these images look extremely dense, "The human brain would look 25 times as complicated," says Wedeen.

You can also see a short but powerfull video on a normal human subject using the same technique, and a related article with a rich gallery of images.