Science Update July 19, 2006
Brain Changes Mirror Symptoms in ADHD
The severity of attention deficit hyperactivity disorder (ADHD) symptoms in youth appears to be reflected in their brain structure, recent NIMH-supported brain imaging studies are finding. In one study, researchers found that the front part of the brain's memory hub, the hippocampus, tended to be enlarged in ADHD, particularly in children with fewer symptoms. They suggest that such changes might develop as a compensatory response that helps the child cope with the impatience and stimulus-seeking problems of the disorder.
The researchers also found that parts of an emotion-processing hub, the amygdala, were smaller in children with the disorder. The diminished size had a significant and positive correlation with severity of ADHD symptoms. In those with the disorder, researchers also observed poor connections between the amygdala and the pre-frontal cortex, which could contribute to problems with impulse control and goal-directed behaviors.
Drs. Kerstin Plessen and Bradley Peterson (Columbia University; New York State Psychiatric Institute; University of Bergen, Norway; and Pennsylvania State University) and colleagues used magnetic resonance imaging (MRI) to scan 51 children and adolescents with ADHD and 63 healthy peers in the study, reported in the July 3, 2006, issue of the Archives of General Psychiatry.
In another recent MRI study, NIMH intramural researchers found that parts of the brain's outer layer that controls attention is thinner in youth with ADHD and remains thin in those with less improvement, perhaps contributing to their impaired recovery. However, in teens who showed improvement, the cortex thickened on the right side, suggesting how brain changes may help explain improvements in coping with ADHD, report Drs. Philip Shaw and Judith Rapoport, NIMH Child Psychiatry Branch, and colleagues.
The 3-5 percent of school-age children with ADHD tend to be constantly impulsive, and inattentive. The disorder is thought to stem from brain circuit abnormalities. Symptoms improve in as many as a third or more of children with the disorder by their late teens. Yet, while previous NIMH imaging studies had shown that most parts of the brain are relatively smaller in ADHD, they did not look at how these differences might be related to clinical outcome.
To study this, researchers scanned the brains of 163 children with ADHD and 166 healthy controls, averaging about 9 years old. They re-scanned about 60 percent of each group again about 5.7 years later.
The ADHD group initially had a thinner cortex, most prominently in frontal areas that control attention and motor activity. These changes turned out to be much greater in patients who showed less improvement at follow-up, about six years later. In children with the best outcomes, an area of the cortex associated with attention (right parietal cortex) had increased thickness and resembled that of healthy peers by follow-up.
"The apparent normalization of cortical thickness in the better outcome youth may reflect a persistence of neural connections that provides an extended period for the sculpting of complex brain circuits supporting attention," suggested Shaw.
Despite the promise of the new findings, MRI brain scans are still an experimental research tool and cannot yet be used to diagnose or predict outcomes for individuals with ADHD, cautioned Shaw.
Shaw P, Lerch J, Greenstein D, Sharp W, Clasen L, Evans A, Giedd J, Castellanos FX, Rapoport J. Longitudinal mapping of cortical thickness and clinical outcome in children and adolescents with attention-deficit/hyperactivity disorder. Arch Gen Psychiatry. 2006 May;63(5):540-9.
Plessen KJ, Bansal R, Zhu H, Whiteman R, Amat J, Quackenbush GA, Martin L, Durkin K, Blair C, Royal J, Hugdahl K, Peterson BS. Hippocampus and Amygdala Morphology in Attention-Deficit/Hyperactivity Disorder. Arch Gen Psychiatry. 2006 Jul;63(7):795-807.
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