Vidyya Medical News Service
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Volume 6 Issue 311 Published - 14:00 UTC 08:00 EST 6-Nov-2004 Next Update - 14:00 UTC 08:00 EST 7-Nov-2004
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Images of the maturing brain

The brain's center of reasoning and problem-solving is among the last to mature, a new study graphically reveals. A decade-long magnetic resonance imaging (MRI) study of normal brain development in people from ages four to 21 shows that the higher-order brain centers don't fully develop until young adulthood.

Researchers long believed that a spurt of overproduction of gray matter — the working tissue of the brain's cortex — during the first 18 months of life was followed by a steady decline as unused brain circuitry was discarded. Then, in the late 1990s, NIMH's Dr. Jay Giedd, a co-author of the current study, and his colleagues discovered a second wave of overproduction of gray matter just prior to puberty, followed by a second bout of "use-it-or-lose-it" pruning during the teen years.

In the new study, researchers at NIH's National Institute of Mental Health (NIMH) and the University of California Los Angeles (UCLA) scanned 13 healthy children and teens every two years for 10 years. After lining the scans up with each other using an intricate set of brain anatomical landmarks, they visualized the ebb and flow of gray matter in maps that, together, form a 3-D time-lapse movie that compresses 15 years of human brain maturation into seconds.

The new movie shows gray matter diminishing in a back-to-front wave, likely reflecting the pruning of connections between brain cells that have remained unused during the teen years. The first areas of the brain to mature are those with the most basic functions, such as processing the senses and movement. Areas involved in spatial orientation and language follow. Areas with more advanced functions — integrating information from the senses, reasoning and other "executive" functions — mature last. This sequence of maturation also roughly parallels the evolution of the mammalian brain, the researchers suggest.

Dr. Judith Rapoport, one of the NIMH researchers, said, "To interpret brain changes we were seeing in neurodevelopmental disorders like schizophrenia, we needed a better picture of how the brain normally develops."

In a study published a few years ago, Rapoport and her colleagues discovered an exaggerated wave of gray matter loss in teens with early onset schizophrenia. These teens, who became psychotic prior to puberty, lost four times the normal amount of gray matter in their frontal lobes, suggesting that childhood onset schizophrenia may be an exaggeration of a normal process. By contrast, children with autism show an abnormal back-to-front wave of gray matter increases, rather than decreases, suggesting that autism may also involve an abnormal brain "pruning" process.

— Written by Jules Asher

Source: PNAS 101,21:8174-8179

To see the time-lapse imaging movie, go to http://www.nimh.nih.gov/press/prbrainmaturing.mpeg. For more information about the development of the teen brain, see http://www.nimh.nih.gov/publicat/teenbrain.cfm



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