Younger Children with ADHD Symptoms Have Reduced Brain Size

E. Mark Mahone, PhD, ABPP, research scientist, Kennedy Krieger Institute

E. Mark Mahone, PhD, ABPP

A new study reveals that children as young as 4 years old with symptoms of attention-deficit/hyperactivity disorder (ADHD) showed reduced brain volumes in regions essential for behavioral control.

The study represents the first comprehensive examination of cortical brain volume in preschool children with ADHD, providing an indication that anomalous brain structure is evident in early development stages.

“These findings confirm what patients have known for a while — even in very young children, ADHD is a real biological condition with pronounced physical and cognitive manifestations,” lead study author, E. Mark Mahone, PhD, ABPP, research scientist, Kennedy Krieger Institute, said in a statement.

The study used high-resolution anatomical MRI scans, as well as cognitive and behavioral measures to study the brain development of 90 medication-naïve preschoolers between 4­—5 years old (52 with ADHD, 38 controls; 64.4% boys).

Study researchers concluded that preschoolers with ADHD showed significantly reduced brain volume across multiple regions of the cerebral cortex, including the frontal, temporal and parietal lobes.

According to researchers, ADHD-related reductions in specific sub-regions (left prefrontal, left premotor, left frontal eye field, left M1 and right supplementary motor complex) were significantly correlated with an increase of symptoms — higher ratings of hyperactive/impulsive symptoms were associated with reduced cortical volumes. Brain regions that showed the greatest ADHD-related reductions were those known for cognitive and behavioral control and predictability of behavioral symptoms.

"It is our hope that with earlier (and accurate) identification of ADHD, it will allow for earlier and more targeted treatments, including behavioral, psychosocial, educational and medical," Mahone told MD Magazine. "As a general principle, earlier intervention for children with neurodevelopmental disorders (such as ADHD) can lead to better outcomes and reduced functional problems associated with the condition."

To address the challenge and difficulty of MRI research in young children, particularly those with ADHD, researchers employed an individualized behavioral desensitization procedure with a mock scanner in order to help prepare children for scans. According to Mahone, this led to a nearly 90% success rate.

"Diagnosing ADHD in young children can be challenging, and requires a thorough examination to understand how the observed behaviors reflect the overall functioning of the child in the context of his/her overall environment," Mahone said. "In order to accurately diagnose ADHD in young children, a variety of other factors and conditions need to be considered and alternative diagnoses ruled out. These other factors include (but are not limited to) situational stress, other developmental disorders (e.g., Autism, Language Disorders), other psychiatric conditions (mood disorders, anxiety), and/or a host of medical factors."

This is the first phase of a study that will follow a preschool age cohort into adolescence. From the study, researchers hope to identify early biological signs that will help predict children most at risk for developing ADHD.

“By understanding the brains of children who grow into the disorder as well as those who grow out of it, we can begin to implement targeted, preventative interventions in young children with the goal of reducing adverse outcomes or even reversing the course of this condition,” Mahone concluded.

In the preschool years, ADHD is the most commonly diagnosed form of psychopathology, and in early childhood, ADHD is associated with significant long-term health and economic costs. Despite children with ADHD presenting symptoms early in preschool years, studies assessing structural brain development in children with ADHD have examined school-aged samples.

This study carefully identified ADHD symptoms closer to onset, which provided researchers a better understanding of brain mechanisms associated with the onset of ADHD.

This study, "Anomalous Brain Development Is Evident in Preschoolers With Attention-Deficit/Hyperactivity Disorder" was funded by the National Institute of Health (NIH) and published in the Journal of the International Neuropsychological Society.