Hyperactive children have smaller and less mature brains

According to a recent study children with attention deficit hyperactivity disorder (ADHD) often have slightly smaller and less mature brains than their peers, which may dampen the signals between the brain's regions. The study sponsored by the National Institute of Mental Health also proved that the stimulants commonly prescribed to treat the problem were not to blame for any brain shrinkage.

The study was carried out at the New York University School of Medicine, USA. Based on magnetic resonance images made of the brains of nearly 300 children over a decade, brain size was found to correlate to the disorder's severity and to persist with age. Brain development appeared healthy in children with the disorder, though the maturation process was on a lower track. On average, the brains of children with the disorder were roughly 3 percent smaller than children without the conditions as control subjects. Where the difference in size might be important was in the cerebellum and the volume of white matter. The cerebellum helps control physical coordination and may also serve as a 'metronome,' providing timing information and coordinating signals between brain regions, which is found in all the four lobes of the brain. Children with the disorder are often described as less mature than their peers and this may relate to delays in white matter maturation.

Between 3 percent and 5 percent of American children are diagnosed with ADHD, three times as many boys as girls. But there is no definitive marker for the condition other than a reduced ability to concentrate, difficulty in organising tasks and belongings, and hyperactive, impulsive behaviour. The study also provides a certain amount of reassurance that medications are not reducing brain size in children with the disorder. It is possible that medication may promote brain maturation. Since the drug (Ritalin) was found not to be responsible for brain shrinkage, the researchers concluded that the disorder may be caused by an injury to the brain early in life or may have a genetic component. The disorder is known to run in families.