A new NIH study suggests a delay in brain development, rather than a total alteration in normal development, is the instigating factor for attention-deficit/hyperactivity disorder (ADHD).
In the current investigation, researchers expanded an earlier study that found thickening of the brain’s cerebral cortex is delayed in children diagnosed with ADHD.
The cerebral cortex is the folded gray tissue that makes up the outermost portion of the brain, covering the brain’s inner structures. This tissue has left and right hemispheres and is divided into lobes.
Each lobe performs specific and vitally important functions, including attention, cognition, language, and sensory processing.
Two dimensions of this structure are cortical thickness and cortical surface area, both of which mature during childhood as part of the normal developmental process.
In the study, published in Biological Psychiatry, researchers set out to measure whether surface area development is delayed in a similar manner to the thickening process. To do this they recruited 234 children with ADHD and 231 typically developing children.
Each child was scanned with neuroimaging equipment up to four times. The first scan was taken at about age 10, and the final scan was around age 17.
Using advanced neuroimaging technology, researchers were able to map the trajectories of surface area development at over 80,000 points across the brain. They found that the development of the cortical surface is delayed in frontal brain regions in children with ADHD.
For example, the typically developing children attained 50 percent peak area in the right prefrontal cortex at a mean age of 12.7 years, whereas the ADHD children didn’t reach this peak until 14.6 years of age.
“As other components of cortical development are also delayed, this suggests there is a global delay in ADHD in brain regions important for the control of action and attention,” said Dr. Philip Shaw, a clinician studying ADHD at the National Institute of Mental Health and first author of this study.
“These data highlight the importance of longitudinal approaches to brain structure,” commented Dr. John Krystal, Editor of Biological Psychiatry. “Seeing a lag in brain development, we now need to try to understand the causes of this developmental delay in ADHD.”
Investigators believe the finding suggests genes that control the timing of brain development are linked to development of ADHD.
As such, Shaw believes researchers should “search for genes that control the timing of brain development in the disorder, opening up new targets for treatment.”