ABSTRACT
Attention de®cit hyperactivity disorder (ADHD) is in some respects a cognitive analogue of Tourette's syndrome, with respect to impulsivity and disinhibition; similarly, it contrasts with the focused preoccupations of obsessive compulsive disorder (OCD), and the inertia of melancholic depression. However, unlike these other disorders, it perhaps impacts rather more upon other members of society than upon the affected individual. In this chapter we shall review criteria and problems in diagnosis (and possible over-diagnosis), the existence of two possible variants of the disorder, comorbidities, how it may continue into adulthood, and possible environmental determinants. We shall see that, like so many of the neurodevelopmental frontostriatal disorders, there is probably an inherited susceptibility, with vulnerability genes perhaps able to be turned on or off at various developmental phases. We shall review possible genetic mechanisms, and the role of modulatory neurotransmitters, particularly dopamine, serotonin, and possibly noradrenaline. Although there may be morphometric correlates of the disorder, we shall see that a neurochemical imbalance may be a more important factor, as perhaps with Tourette's syndrome, OCD and depression, though as with schizophrenia we cannot discount possible structural changes. We shall review the neuropsychology of the disorder, particularly with reference to executive functions and inhibitory
processes. As with Tourette's syndrome and OCD, many of the characteristic features of ADHD are normally present in most children younger than a certain age; we shall ®nally, therefore, address the possibly adaptive aspects of the ``disorder'' in certain selective or environmental contexts.
