Aspects of attention deficit hyperactivity disorder (ADHD) may persist into adulthood, even when current diagnostic measures fail to identify its presence, according to new research published in the journal European Child Adolescent Psychiatry.
The findings show that young adults who had been diagnosed with ADHD in adolescence have differences in brain structure and perform poorly in memory tests compared to their peers.
Some experts have speculated that as the brain develops in adulthood, children may grow out of ADHD, but until now there has been minimal rigorous research to support this.
So far, most studies that have followed up on children and adolescents with ADHD into adulthood have focused on interview-based assessments, leaving questions of brain structure and function unanswered.
Current estimates suggest that between 10-50 percent of children with ADHD still have it as adults. Diagnosis in adulthood is currently reliant on meeting symptom checklists (such as the American Psychiatric Association’s Diagnostic and Statistical Manual).
For the new study, researchers from the University of Cambridge, UK, and the University of Oulu, Finland followed 49 adolescents diagnosed with ADHD at age 16. They examined their brain structure and memory function in young adulthood, at 20-24 years old, and compared the findings to a control group of 34 young adults.
The researchers found that the group diagnosed in adolescence still had problems in terms of reduced brain volume and poorer memory function, regardless of whether or not they still met diagnostic checklist criteria for ADHD.
Through magnetic resonance imaging (MRI) brain scans, the researchers found that the adolescents with ADHD had reduced grey matter in the caudate nucleus, a key brain region that integrates information across different parts of the brain, and supports important cognitive functions, including memory.
To find out whether these grey matter deficits were of any importance, the researchers conducted a functional MRI experiment (fMRI), which measured brain activity while the participants took a test of working memory inside the scanner.
One-third of the adolescents with ADHD failed the memory test compared to less than one in twenty of the control group (an accuracy of less than 75 percent was classed as a fail).
Even among the adolescent ADHD sample who passed the memory test, the scores were on average six percentage points less than controls. There were no differences in brain structure or memory test scores between those young adults previously diagnosed with ADHD who still met the diagnostic criteria and those who no longer met them.
“In the controls, when the test got harder, the caudate nucleus went up a gear in its activity, and this is likely to have helped solve the memory problems. But in the group with adolescent ADHD, this region of the brain is smaller and doesn’t seem to be able to respond to increasing memory demands, with the result that memory performance suffers,” says study leader Dr. Graham Murray from the Department of Psychiatry, University of Cambridge.
“We know that good memory function supports a variety of other mental processes, and memory problems can certainly hold people back in terms of success in education and the workplace. The next step in our research will be to examine whether these differences in brain structure and memory function are linked to difficulties in everyday life, and, crucially, see if they respond to treatment.”
The fact that the study was set in Finland, where medication is rarely used to treat ADHD, meant that only one of the 49 ADHD adolescents had been treated with medication. Therefore, the researchers were able to confidently rule out medication as a confounding factor.
Source: University of Cambridge