By Merritt McKinney
NEW YORK, Sep 20 (Reuters Health) -- Two new reports suggest that the brain does not stop developing in early childhood, as previously believed, but continues to mature throughout adolescence.
According to Dr. Jay Giedd, of the National Institute of Mental Health in Bethesda, Maryland, it has long been known that babies have an overabundance of brain cells. As the brain matures, these cells engage in a fierce battle for survival, he told Reuters Health in an interview. Normally, cells essential for important tasks prevail, but in some children, such as those who are autistic, brain cells needed for language do not survive, he explained.
Now, in a study that followed a group of children through their teen years, Giedd and his colleagues have detected signs that the brain undergoes a second wave of brain development during adolescence.
The study showed that white matter, which connects different parts of the brain, increased steadily as children aged, but the gray matter -- the thinking, processing parts of the brain -- had a growth spurt during the preteen years. This growth peaked about a year earlier in girls, perhaps because girls tend to mature at a younger age, the researchers write in the October issue of the journal Nature Neuroscience.
"After this second wave, these brain cells fight it out again," Giedd said. His team observed that gray matter began to decline after adolescence.
But unlike what happens in the battle of the brain cells in early childhood, in which the winners are largely determined by genetics, a teenager's activities appear to have an effect on which brain cells survive, Giedd said.
"Teenagers have the opportunity, in a sense, to hardwire their own brains," he explained. Referring to the brain, he said it is important to 'use it or lose it,' noting that cells that are used get more nutrients and growth factors which help them thrive.
In the second study, a team led by Dr. Elizabeth R. Sowell, of the University of California at Los Angeles, report that gray matter in certain parts of the brain declines between adolescence and young adulthood. The largest drop in gray matter occurred in a region of the brain known as the frontal cortex. The researchers detected few changes in gray matter in other parts of the brain, however.
It makes sense that the frontal lobes of the brain take longer to mature, Sowell and her colleagues note, since these parts of the brain are largely responsible for planning difficult tasks, controlling emotions and inhibiting inappropriate behavior -- abilities that many people do not master until they are in their late teens or early 20s. Likewise, it is not surprising that the parts of the brain that control language and the senses, which develop at an earlier age, did not show much change in gray matter, according to the report.
