As an individual who has struggled with severe ADD, i've followed scientific and medical journal research in the field. New research, involving brain-scans of intelligent ADD and non-ADD brains, shows a specific recall disorder. Basically, when an ADD brain wants to concentrate on a single task (reading/listening to a lecture for example), other regions of the brain are called upon and interfere with focus. This is why many ADD/ADHD individuals like myself, hide in the corner of a quite library, with ear-plugs, because sounds/visual-stimulation/other thought process is amplified. With a non-ADD brain, non-recalled regions, unrelated to the requested task, drastically lower activity levels.
Check it out Journal of Psychiatric Research: A. Cubillo et al. / Journal of Psychiatric Research 44 (2010) 629–639
"Reduced activation and inter-regional functional connectivity of fronto-striatal networks in adults with childhood Attention-Deficit Hyperactivity Disorder (ADHD) and persisting symptoms during tasks of motor inhibition and cognitive switching."
Check it out Journal of Psychiatric Research: A. Cubillo et al. / Journal of Psychiatric Research 44 (2010) 629–639
"Reduced activation and inter-regional functional connectivity of fronto-striatal networks in adults with childhood Attention-Deficit Hyperactivity Disorder (ADHD) and persisting symptoms during tasks of motor inhibition and cognitive switching."