New research has found that the brains of preschoolers who show symptoms of attention deficit hyperactivity disorder (ADHD) may have smaller brains and differences in neural connectivity compared to their peers.

The study, published online in the Journal of the International Neuropsychological Society, found that children with symptoms of ADHD have a smaller brain volume overall and size reductions in specific regions including the frontal lobe. The researchers concluded the magnitude of said reductions predict how bad a child's ADHD symptoms will be as early as 4 years old, according to a March 26 article in The New York Times.

Lead study author Mark Mahone, PhD, director of the department of neuropsychology at Kennedy Krieger Institute in Baltimore, and his colleagues analyzed high-resolution brain scans of 90 children, 4 to 5 years of age. In addition, none of the children had ever taken medication for ADHD.

Mahone and his team found 52 of the 90 children had symptoms of ADHD and smaller brain volume, compared to the 38 other matched controls who were similar in age, gender, socioeconomic status, IQ and language function.

“There are structural differences in brain volumes, there are connections between brain regions reflected in white matter changes in people with ADHD, there are chemical changes in some of the major transmitter systems in the brain,” Mahone told The New York Times. “When the brain is asked to do something, the brains of children with ADHD do the same task, but the brain is less efficient. Very clear evidence of things happening differently in the brain helps us reinforce that this [ADHD] is a very real condition with onset very early in life.” 

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