Organic injury to the brain can have complex and interacting psychological effects, not only at the level of intellectual impairment but also at the levels of affective and behavioural disturbance. These sequelae may be directly or indirectly caused by the brain injury, and may vary in severity from those which are gross and obvious to those which are subtle and detectable only on detailed assessment. Nevertheless, even those which are subtle can have pervasive effects on a patient's social and occupational functioning, whilst those which are gross may arise from a variety of causes with different treatment implications. In either case, neuropsychological assessment can be highly germane to clarification of the problem, to prediction of the functional consequences and to the development of appropriate interventions or environmental adaptations.

To illustrate this, consider the case of a young man who has sustained a head injury in an assault. A year after the incident he has made a good physical recovery, but is very aggressive and has lost his job as a sales manager because of hostility towards colleagues and a general lack of organization in his work. These problems might, on the one hand, arise from organic damage to regions of the brain involved in the genesis or inhibition of aggression, or, on the other, be a psychological reaction to some more subtle cognitive deficit such as a generalized reduction in the efficiency with which information is processed or a mild but specific impairment of memory.