The biopsychosocial model
The biopsychosocial model introduced by George Engel in the late 1970s (see Engel, 1977) adopts the perspective that a full understanding of mental distress, as well as of mental health and well-being, involves a study of the biology of the body (usually with an emphasis upon the brain), an individual’s psychology and their social circumstances. According to this model, disease defined simply in terms of biology, is not a useful way of approaching distress and well-being.
A central assumption behind the biopsychosocial model is that, not only do the three factors −biological, psychological and social − play a role in any form of psychological distress or well-being, but also that there is interdependence between them. For example, changing an individual's social circumstances can change his or her psychology. Changing an individual's psychology can change their social interactions. Changing a person's psychological state will also change the activity of their brain. A change in the underlying brain activity, for example as a consequence of traumatic brain injury or a physical illness, can change the individual’s psychological state and their behaviour. In these terms, biology is not an absolute defining criterion of when there is mental distress, but neither is it irrelevant. A biological explanation can contribute to mental distress, but should be considered as one contributory factor amongst three.
In health or ill-health, biological and psychological contributions will always be present. In one sense, in the very rare cases of, for example, a person living alone on a desert island or a hermit in a cave, there will not be a social factor present. However, such a person will still have had a history of earlier social interactions which will have left their mark. So, according to a biopsychosocial model, the relevant question is not which factor, ‘bio’, ‘psycho’ or ‘social’, is the most important, since they are interdependent. At whichever level a change arises, there will be consequences for the other two. For example, a social change, such as finding a new job, a marriage, divorce or a bereavement (the loss of a loved one), will have obvious implications for a person's psychology, which simultaneously affects the brain. But a change does not necessarily occur in only one of the three factors at any one time.