National Geographic : 2014 Feb
38 national geographic • February 2014 through Advancing Innovative Neurotechnolo- gies (BRAIN) Initiative. In an announcement last spring President Barack Obama said that the large-scale project aimed to speed up the map- ping of our neural circuitry, “giving scientists the tools they need to get a dynamic picture of the brain in action.” As they see the brain in action, neuroscien- tists can also see its flaws. They are starting to identify differences in the structure of ordinary brains and brains of people with disorders such as schizophrenia, autism, and Alzheimer’s dis- ease. As they map the brain in greater detail, they may learn how to diagnose disorders by their effect on anatomy, and perhaps even un- derstand how those disorders arise. On my return trip to his lab Wedeen finally locates the image from my session in the scanner. My brain appears on his screen. His technique, called diffusion spectrum imaging, translates ra- dio signals given off by the white matter into a high-resolution atlas of that neurological Internet. His scanner maps bundles of nerve fibers that form hundreds of thousands of pathways carrying information from one part of my brain to another. Wedeen paints each path a rainbow of colors, so that my brain appears as an explosion of colorful fur, like a psychedelic Persian cat. Wedeen focuses in on particular pathways, showing me some of the circuitry important to language and other kinds of thought. Then he pares away most of the pathways in my brain, so that I can more easily see how they’re organized. As he increases the magnification, something astonishing takes shape before me. In spite of the dizzying complexity of the circuits, they all intersect at right angles, like the lines on a sheet of graph paper. “It’s all grids,” says Wedeen. When Wedeen first unveiled the grid struc- ture of the brain, in 2012, some scientists were skeptical, wondering if he’d uncovered only part of a much more tangled anatomy. But Wedeen is more convinced than ever that the pattern is meaningful. Wherever he looks—in the brains of humans, monkeys, rats—he finds the grid. He notes that the earliest nervous systems in Cambrian worms were simple grids—just a pair of nerve cords running from head to tail, with runglike links between them. In our own lineage the nerves at the head end exploded into billions but still retained that gridlike structure. It’s pos- sible that our thoughts run like streetcars along these white matter tracks as signals travel from one region of the brain to another. “There’s zero chance that there are not prin- ciples lurking in this,” says Wedeen, peering intently at the image of my brain. “We’re just not yet in a position to see the simplicity.” Scientists are learning so much about the brain now that it’s easy to forget that for much of history we had no idea at all how it worked or even what it was. In the ancient world physicians believed that the brain was made of phlegm. Aristotle looked on it as a refrigerator, cooling off the fiery heart. From his time through the Renaissance, anatomists declared with great authority that our perceptions, emotions, rea- soning, and actions were all the result of “animal spirits”—mysterious, unknowable vapors that swirled through cavities in our head and trav- eled through our bodies. The scientific revolution in the 17th century began to change that. The British physician Thomas Willis recognized that the custardlike tissue of the brain was where our mental world existed. To understand how it worked, he dissect- ed brains of sheep, dogs, and expired patients, producing the first accurate maps of the organ. It would take another century for researchers to grasp that the brain is an electric organ. Instead of animal spirits, voltage spikes travel through it and out into the body’s nervous system. Still, even in the 19th century scientists knew little about the paths those spikes followed. The Italian phy- sician Camillo Golgi argued that the brain was a seamless connected web. Building on Golgi’s research, the Spanish scientist Santiago Ramón y Cajal tested new ways of staining individual burrowing down to single nerve cells may finally provide answers to basic questions about the brain. Carl Zimmer wrote on bringing back extinct species in the April 2013 issue. Robert Clark’s previous story, on sugar, was in the August 2013 issue.