Researchers used tens of thousands of magnetic resonance imaging scans to map how the brain’s outer layer matures during adolescence. Credit: Zephyr/Science Photo Library

The speed at which regions of the brain mature during early adolescence can forecast the emergence of mental-health conditions up to four years before symptoms develop, according to a study of nearly 12,000 young people in the United States.

Your brain expands and shrinks over time — these charts show how

By tracking the brains of adolescents over six years in nearly 30,000 scans, researchers mapped how the brain’s outer layer, the cerebral cortex, thins as children grow into teenagers. The team observed that sensory areas of the cortex thinned, or matured, first, followed by regions responsible for complex thought.

The findings, posted on 11 October on the preprint server bioRxiv 1 , ahead of peer review, challenge the theory that psychiatric disorders are caused by defects in specific brain circuits.…