Attention-deficit hyperactivity disorder (ADHD) affects some 5 percent of kids ages 18 and younger with symptoms of inattention, impulsivity, and hyperactivity. Two out of three continue to have symptoms as adults.

A study published in The Lancet Psychiatry indicates that ADHD patients have smaller brains than those without the disorder.

The investigation included more than 3,000 volunteers ages 4 to 63; about half of them had ADHD. In the ADHD group, brain areas that control attention, memory, and emotion were significantly smaller.

The greatest differences in regional brain size were seen in the amygdala, which is the emotional control center of the brain. Smaller brain volumes were also striking in the children and adolescents with ADHD.

The fact that the greatest atrophy was seen in the brain’s emotional control center helps explain the emotional reactivity and low frustration tolerance in many of these patients.