Description text

To calculate the path of each bundle of fibers in the brain, scientists first create a three-dimensional picture of the direction of water diffusion for each voxel, or three-dimensional pixel, in the brain scan. The peanut-shaped blobs in this image of Wedeen’s own brain stem represent the speed of diffusion in every possible direction. Given that shape, scientists infer the most likely path of the nerve fibers passing through that spot, following the principle that water diffusion is parallel to fibers. In this case, the large vertical balloons indicate fibers running vertically, while the smaller horizontal peaks suggest fibers going in another direction.