The three expressions of the clinical syndrome of dementia have been well documented: cognitive deficitsamnesia, aphasia, apraxia, and agnosia; neuropsychiatric featuresa heterogeneous array of psychiatric symptoms and behavioural disturbances such as depression, delusions, hallucinations, misidentifications, aggression, agitation, wandering, collectively described as neuropsychiatric features, behavioural and psychological symptoms of dementia (BPSD),¹ or non-cognitive features²; and problems with activities of daily living. The history of interest in the neuropsychiatry of dementia is relatively short by comparison with research into cognitive dysfunction. Psychiatric symptomatology was only first described in detail in the 1980s and 1990s and has only recently been the subject of standardised and reliable methods of assessment (for example, the neuropsychiatric inventory³). In the paper by Holmes et al (this issue pp 777-779),⁴ the field takes a significant step forward in identifying some of the biological determinants of the expression of neuropsychiatric symptoms in Alzheimer's . . . [Full text of this article]