All illness has both psychological and physical dimensions. This may seem a startling claim, but on reflection it is uncontroversial. Diseases don’t come to doctors, patients do—and the processes by which patients detect, describe, and ponder their symptoms are all eminently psychological. This theoretical point has practical implications. If we adopt a “bio-psycho-social” approach to illness generally, one which recognises the biological, psychological, and social aspects of our lives, we become less likely to neglect the treatable psychological origins of many physical complaints (from globus hystericus to full blown conversion disorder) and the treatable psychological consequences (such as depression and anxiety) of much physical disease.

NEUROLOGY, PSYCHOLOGY, AND PSYCHIATRY

Neurology has an especially close relationship with psychology and psychiatry, as all three disciplines focus on the functions and disorders of a single organ, the brain. The main targets of the traditional British “neurological examination” may be elementary motor and sensory processes, but any adequate assessment of “brain function” must take account of cognition and behaviour. The notion many of us bring to neurology—that only a minority of neurological disorders has a significant psychological or psychiatric dimension—is almost certainly wrong. Cognitive and behavioural involvement is the rule, not the exception, among patients with disorders of the central nervous system (CNS). The physical and psychological symptoms of disease can therefore be related in the following ways: (1) physical symptoms come to light by way of complex psychological processes; (2) psychological upset can manifest itself in physical symptoms; (3) physical diseases commonly cause a secondary psychological reaction; (4) one category of physical disease, affecting the brain, can give rise, more or less directly, to psychological manifestations.

The importance of a wide ranging approach to assessment is well illustrated by the example of dementia, a primarily cognitive and behavioural disorder: the clue to diagnosis may come from general …