Young adults diagnosed with attention deficit/hyperactivity disorder (ADHD) in adolescence show differences in brain structure and perform poorly in memory tests compared to their peers, according to new research from the University of Cambridge, UK, and the University of Oulu, Finland.
The findings, published in the journal European Child Adolescent Psychiatry, suggest that aspects of ADHD may persist into adulthood, even when current diagnostic criteria fail to identify the disorder.
ADHD is a disorder characterised by short attention span, restlessness and impulsivity, and is usually diagnosed in childhood or adolescence. Estimates suggest that more than three in every 100 boys and just under one in every 100 girls has ADHD. Less is known about the extent to which the disorder persists into adulthood, with estimates suggesting that between 10-50% of children still have ADHD in adulthood. Diagnosis in adulthood is currently reliant on meeting symptom checklists (such as DSM-5).
Some have speculated that as the brain develops in adulthood, children may grow out of ADHD, but until now there has been little rigorous evidence to support this. So far, most of the research that has followed up children and adolescents with ADHD into adulthood has focused on interview-based assessments, leaving questions of brain structure and function unanswered.
Now, researchers at Cambridge and Oulu have followed up 49 adolescents diagnosed with ADHD at age 16, to examine their brain structure and memory function in young adulthood, aged between 20-24 years old, compared to a control group of 34 young adults. The research was based within the Northern Finland Birth Cohort 1986, which has followed up thousands of children born in 1986 from gestation and birth into adulthood. The results showed that the group diagnosed in adolescence still had problems in terms of reduced brain volume and poorer memory function, irrespective of whether or not they still met diagnostic checklist criteria for ADHD.
By analysing the structural magnetic resonance imaging (MRI) brain scans and comparing them to the controls, the researchers found that the adolescents with ADHD had reduced grey matter in a region deep within the brain known as the caudate nucleus, a key brain region that integrates information across different parts of the brain, and supports important cognitive functions, including memory.
The research was funded in part by the Medical Research Council, with additional support from the Wellcome Trust and the NIHR Cambridge Biomedical Research Centre.