ATTENTION DEFICIT HYPERACTIVITY DISORDER - FROM BRAIN DYSFUNCTIONS TOBEHAVIOR/

This special issue represents an attempt to answer fundamental brain a nd behaviour issues in attention-deficit hyperactivity disorder (ADHD) . The European network on hyperkinetic disorders (Eunethydis) is tryin g to develop a novel, testable theory of ADHD, giving an account of it s causes, its development from brain dysfunctions to behavioural sympt oms and co-morbidity and explaining why no current therapy produces lo ng-lasting improvements. The combined insights of the articles present ed here suggest that there is no brain damage in ADHD, but hypo-effici ent dopamine systems which give rise to neurochemical imbalances. Thes e cause behavioural problems: deficits in sustained attention, overact ivity and impulsiveness. Impulsiveness is increasingly being seen as a key characteristic of the disorder. None of these symptoms are necess arily primary, but may be secondary to an underlying deficit in reinfo rcement processes seen particularly in a greater than normal sensitivi ty to variations in the timing of stimulus presentation. Other symptom s can also be seen: altered effects of reinforcers, increased behaviou ral variance and motor co-ordination problems. Medication produces tem porary, plastic changes in cellular components like receptors and tran sduction mechanisms normalising dopamine functions and behaviour. (C) 1998 Elsevier Science B.V. All rights reserved.