In 1845, Wilhelm?Griesinger, author of the most important textbook of psychiatry of the day,?wrote: ¡°what organ must necessarily and invariably be diseased where?there is?madness? ¡­ Physiological and pathological facts show us that this organ can?only be the brain¡­¡±?Griesinger¡¯s truism?is regularly reiterated in our own time?because it expresses the basic?commitment of contemporary biological psychiatry.

The logic of?Griesinger¡¯s argument seems unassailable: severe mental illness has to?originate in a physiological abnormality of some part of the body, and the only?plausible candidate location is the brain.?Since?the mind is nothing over and above the activity of the brain, the disordered?mind is nothing more than a disordered?brain. True enough. But that is not to?say that mental disorders can, or will, be described by genetics and?neurobiology. Here¡¯s an analogy. Earthquakes are nothing?over and above the?movements of a vast number of atoms in space, but the theory of earthquakes?says nothing at all about atoms but only about tectonic plates. The?best?scientific explanation of a phenomenon depends on where real human beings find?comprehensible patterns in the universe, and not how the universe is?constituted. God may understand earthquakes and mental illness in terms of?atoms, but we may not have the time or the intelligence to do so.

It¡¯s?not a radical idea that understanding and treating brain disorders sometimes?has to move outside the skull.?A?man's heart hurls an embolus into his brain. He?might now be unable to produce?or understand speech, move one half of his body, or see half of the world in?front of him. He has had a stroke and his brain is now?damaged. The?cause of his brain illness did not originate there, but in his heart. His?physicians will do what they can to limit further damage to his brain tissue?and?perhaps even restore some of the function lost due to the embolism. But?they will also try to diagnose and treat his cardiovascular disease. Is he in?atrial fibrillation??Is his mitral valve prolapsed? Does he require blood?thinner? And they won't stop there. They will want to know about the patient's?diet, exercise regimen, cholesterol?level and any family history of heart?disease.

Severe mental illness is also an assault on the brain. But?like the embolus it may sometimes originate outside the brain. Indeed,?psychiatric research has already?given?us clues suggesting that a good theory of mental illness will need concepts?that make reference to things outside the skull. Psychosis provides a good?example.?A family of disorders, psychosis?is marked by hallucinations and delusions. The central form of psychosis,?schizophrenia, is?the?psychiatric brain?disease?par?excellence.?But schizophrenia interacts with the?outside world, in particular, the social world. Decades of research has given?us robust evidence that the risk of?developing schizophrenia goes up with?experience of childhood adversity, like abuse and bullying. Immigrants are at?about twice the risk, as are their children. And?the risk of illness increases?in a near-linear fashion with the population of your city?and varies with the social?features of neighborhoods.?Stable,?socially coherent?neighborhoods have a lower incidence than neighborhoods that?are more transient and less cohesive. We don¡¯t yet understand what it is about?these social?phenomena that interacts with schizophrenia, but there is good?reason to think they are genuinely social.

Unfortunately,?these environmental determinants of psychosis go largely ignored, but they?provide opportunities for useful interventions. We don¡¯t yet have a genetic?therapy for schizophrenia, and antipsychotic drugs can only be used after the?fact and are not nearly as good as we¡¯d like them to be.?The Decade of the Brain?produced?a great deal of important research into brain function, and the new BRAIN?initiative will do so as well. But almost none of it has yet (or is likely) to?help the?patients who suffer from mental illness or those who treat them.?But reducing child abuse, and improving?the quality of the urban environment might very well prevent?some people from?ever developing a psychotic illness at all.

Of course, whatever it is about the?social determinants of psychosis that makes them risk factors, they must have?some downstream effect on the brain otherwise?they would not raise the risk of schizophrenia,?but they themselves are not neural phenomena any more than smoking is a?biological phenomenon because it is a?cause of lung cancer. The theory of?schizophrenia will have to be more expansive, therefore, than the theory of the?brain and its disorders.

That?a theory of mental illness should make reference to the world outside the brain?is no more surprising than that the theory of cancer has to make reference to?cigarette smoke. And yet what is commonplace in cancer research is radical in?psychiatry. The time has come to expand the biological model of psychiatric?disorder?to include the context in which the brain functions. In understanding, preventing?and treating mental illness, we will rightly continue to look into the neurons?and DNA?of the afflicted and unafflicted. To ignore the world around them would?be not only bad medicine but bad science.