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.