Biological models of mental illness: implications for therapy development

Systems approaches are needed to recognise the complexity of the biological bases of psychiatric disease

The bases of mental disorders can best be understood as a complex interplay between biological, psychological, social and lifestyle factors: a classic bio-psycho-social-lifestyle model. There are undoubtedly some disorders where a biological model alone is more appropriate — this applies particularly to the psychotic disorders — but even in such cases it must be acknowledged that these illnesses are strongly influenced by psychosocial and lifestyle factors. What makes a biological understanding of mental illnesses necessary, however, is that it opens the way for the development of rational treatments. This has been the quest since antiquity, with treatments predicated on the putative underlying biological causes: purging and bleeding patients to correct imbalances in the humours to treat melancholia, which was attributed to an excess of black bile, or removing sources of focal infection, such as the teeth, tonsils and even the colon, that were once regarded as causing mental disorders. While these models perhaps now seem far-fetched, they were not entirely implausible when one considers contemporary neuro-endocrine and neuro-inflammatory models of mental illness.