With its 100 billion neurons, the human brain is remarkably difficult to decipher. A report published online this week in the Proceedings of the National Academy of Sciences provides a new, 15-year view of how the organ develops.

Nitin Gogtay of the National Institute of Mental Health (NIMH) and his colleagues recruited 13 healthy volunteers between the ages of four and 21 to have their brains analyzed using magnetic resonance imaging (MRI) every two years. The researchers then applied a novel brain-mapping technique to the 52 resulting scans that allowed them to compare several different brains and map changes in brain volume over time, providing a movie of brain maturation. "To interpret brain changes we were seeing in neurodevelopmental disorders like schizophrenia, we need a better picture of how the brain normally develops," says study co-author Judith L. Rapoport of the NIMH.

The scientists found that the first brain regions to mature are those used to process movement and the five senses. Areas dedicated to spatial organization and language follow, with regions associated with reasoning and other so-called executive functions maturing last. The mapping further revealed that unnecessary neuronal connections get pruned over the years. The authors suggest that alterations to the degree or timing of the basic pattern of maturation could underlie disorders such as autism or childhood-onset schizophrenia.