Medical Research: What is the background for this study? What are the main findings?
Dr. Murray: There is debate about the extent to which ADHD persists into adulthood, with estimates suggesting that between 10-50% of children still have ADHD in adulthood. Diagnosis (whether in childhood or adulthood) is currently reliant on meeting symptom checklists (such as the American Psychiatric Association’s Diagnostic and Statistical Manual), and a current diagnosis is often the prerequisite to access health care from psychiatric services. We decided to follow up a sample of 49 teens who all had a confirmed diagnosis of ADHD at age 16. We also followed a control group made up of comparison healthy volunteers from the same social, ethnic and geographical background.
When we used the symptom checklist criteria of persistence, only 10% of patients still met ADHD diagnostic criteria in adulthood. However, there is more to ADHD than this. When it comes to adult brain structure and function, it didn’t make any difference whether symptom checklists were still met or not. On reaching adulthood, the adolescent ADHD group show reduced brain volume in the caudate nucleus – a key brain region that supports a host of cognitive functions, including working memory function. When we assessed working memory ability, we noted persistent problems in the adolescent ADHD group, with a third of the adolescent ADHD sample failing the memory test. The poor memory scores seemed to relate to a lack of responsiveness in the activity of the caudate nucleus that we could detect using functional MRI scans. In the control group, when the memory questions became more difficult, the caudate nucleus became more active, and this appeared to help the control group perform well; in the adolescent ADHD group, the caudate nucleus kept the same level of activity throughout the test. It was as if, for 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 for the adolescence ADHD group, the caudate couldn’t go up a gear when the test became harder, and this likely resulted in poorer performance. Continue reading