I just found this article:
Disconnect Between Brain Regions in ADHD
January 11, 2010
Two brain areas fail to connect when children with attention deficit hyperactivity disorder attempt a task that measures attention, according to researchers at the UC Davis Center for Mind and Brain and M.I.N.D. Institute.
“This is the first time that we have direct evidence that this connectivity is missing in ADHD,” said Ali Mazaheri, postdoctoral researcher at the Center for Mind and Brain. Mazaheri and his colleagues made the discovery by analyzing the brain activity in children with ADHD. The paper appears in the current online issue of the journal Biological Psychiatry.