Untangling the brain
I
magine the Internet, with its hundreds of millions of links and nodes. Now multiply that by a million. And then by another million, and so on to the 10th power, and then, maybe, you’d begin to approach the complexity of the network that is the human brain. Scientists and philosophers are fond of describing the human brain as the most complex object in the known universe (barring the existence of even more complex brains.) The brain is also surely the most complex network in creation. Neuroscientists estimate that a single cubic millimeter of cerebral cortex contains a billion connections between brain cells, or neurons. A mature human brain in its entirety contains around a million billion connections. Untangled, the wire axons that constitute the brain’s electrical infrastructure would stretch from the Earth to the moon. Add to that sheer volume of neural connections the fact that the wiring changes over time as the organ grows and develops, and the human brain emerges as not only the most complex network in the universe, but also as unique in its structure. In fact, every single brain is unique. Of the approximately six billion human brains on the planet, no two are exactly alike.
However structurally complex, though, a brain isn’t categorically different from other, more basic networks. “On the one hand, the brain is just a bunch of cells connected to each other with wires,” says Olaf Sporns, a professor in the Department of Psychological and Brain Sciences in the College of Arts and Sciences at Indiana University Bloomington. “On the other hand, the brain is the seat of things like thought, memory, emotion, and other high-level cognitive functions.” The ultimate question, Sporns says, is the connection between these two neural phenomena: How do we get from cells and wires to thought and memory? Many scientists have used magnetic resonance imaging (MRI) to record which brain areas light up when people perform tasks, solve problems, and react to stimuli. While such studies have helped identify specific brain regions and assign them roles, they’ve done little to explain how the various parts of the brain communicate and work together. To begin solving this puzzle, Sporns and colleagues at Harvard University and in Switzerland used diffusion MRI technology to create the first-ever complete, high-resolution map of the brain’s neural architecture.
Research & Creative Activity | S P R I N G 2 0 0 9
by Jeremy Shere
41