Instead of nerve fibers travelling willy-nilly through the brain like spaghetti, as some imaging has suggested, the new portraits reveal two-dimensional sheets of parallel fibers crisscrossing other sheets at right angles in a gridlike structure that folds and contorts with the convolutions of the brain.

This same pattern appeared in the brains of humans, rhesus monkeys, owl monkeys, marmosets and galagos, researchers report today (March 29) in the journal Science.

"The upshot is the fibers of the brain form a 3D grid and are organized in this exceptionally simple way," study leader Van Wedeen, a neuroscientist at Harvard Medical School and Massachusetts General Hospital, told LiveScience.