Van Wedeen from Massachusetts General Hospital, who led the study, says that his results came as a complete shock. “I was expecting it to be a pure mess,” he says. Instead, he found a regular criss-cross pattern like the interlocking fibres of a piece of cloth.
For years, scientists have been able to trace the outlines of individual neurons by injecting them with telltale chemicals that migrate along their lengths. But this technique can only be used in dead brains, and it’s small in scale. To get the big picture, Wedeen turned to diffusion magnetic resonance imaging (MRI), a technique that uses magnetic fields to detect the water flowing along our neurons. By tracking these streams, Wedeen mapped the brain’s white matter fibres – the tracts that carry signals from one area to another. They are the original information superhighways, and Wedeen could see huge groups of them at once.
He studied the human brain, as well as those of four primates – the rhesus macaque, owl monkey, marmoset, and galago (or bushbaby).  He started with a single large white matter tract – the equivalent of a motorway. Here’s one in the macaque’s brain, coloured in blue.

Then, Wedeen looked for all the fibres coming off this main tract. Here they are in red, orange and yellow. You can see them branching off perpendicularly in a single curving sheet.

Wedeen did this over and over again, creating stunning images like these – a riot of right angles, arranged in sheet after colourful sheet. “I was astonished,” he says. “[The pattern] was present in every part of every brain of the different species. It was always there.” Wedeen has even found the same patterns in the brains of cats, rats, possums and other animals, although those data have not yet been published.