The iconic image of the brain is a misshapen, yellowish lump. Existing technology can show which parts of the lump light up when people think, but a real understanding of how the brain works demands a better picture of the nerve fibers that ferry electrical signals between brain cells. Those fibers, however, are so small and tangled that researchers haven't been able to see them clearly.

Now, an international team of scientists has combined a new variation on magnetic resonance imaging with mathe­matical analysis to generate the first detailed map of the network of connections in the human cortex, the part of the brain responsible for higher-order thinking.