ADHD’s Impact on the Brain Persists into Adulthood

Evidence suggests that many adults who were diagnosed with attention-deficit/hyperactivity disorder (ADHD) “grow out” of the diagnosis. The estimates for the number of adults who shed their ADHD with age range from 10 to 50 percent. New research suggests that, although some adults who were diagnosed with ADHD as children no longer meet the diagnostic criteria for ADHD, the disorder’s imprint still lingers on the brain. The study, from researchers at the University of Cambridge and University of Oulu in Finland, reveals that ADHD has a lasting impact on the brain and cognitive functions.

The researchers evaluated 49 young adults who were diagnosed with ADHD at age 16 (some kept their diagnosis, while others no longer met the diagnostic criteria at the time of the study) and 34 young adults without ADHD. The study was a follow-up to a larger study: the Northern Finland Birth Cohort 1986.

Using magnetic resonance imaging (MRI), the researchers analyzed the participant’s grey matter volume. Those who had been diagnosed with ADHD in adolescence had reduced grey matter volume in the caudate nucleus, a part of the brain that integrates information from different regions and supports cognitive functions like memory.

To find out if the grey matter deficit affected cognitive function, the researchers next conducted functional MRI (fMRI) scans of some of the participants while they completed a working memory test. One-third of the participants diagnosed with ADHD in adolescence failed the test (a score of 74 percent or less counted as failure). In comparison, only about 1 in 20 of the control group failed the test. Among those who passed in the ADHD group, the average score was six percent lower than that of the controls.

The findings indicate that poor memory scores are related to diminished responsiveness in the caudate nucleus. In control group participants, the caudate nucleus was more active when responding to difficult questions. For those in the ADHD group, caudate nucleus activity was stable throughout the test. This test did not demonstrate a difference in brain structure or memory between those who no longer met the diagnostic criteria for ADHD and those who still had an ADHD diagnosis.

“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,” stated study leader Dr. Graham Murray of Cambridge’s Department of Psychiatry.

This research is published in the journal European Child Adolescent Psychiatry.

Previous news in ADHD:

• Traumatic brain injury: Risk factor for adult ADHD
• Gene groupings suggest a spectrum of ADHD