Research in mental health has moved on from chemical imbalances as the cause of mental illness to circuitry dysfunction in the prefrontal cortex, at least according to Thomas Insel, Director of NIMH. For example, in his article Disruptive insights in psychiatry: Transforming a clinical discipline, he says aspects of schizophrenia can be mapped onto dysfunction of dorsolateral prefrontal circuits that mediate executive function; depression appears to involve dysfunction in a region of the midline infragenual prefrontal cortex important for regulation of mood; OCD (obsessive-compulsive disorder) involves dysfunction in the orbitofrontal prefrontal cortex via its role in perseverative behaviours; and posttraumatic stress disorder (PTSD) can now be mapped to dysfunction in prefrontal circuits required for the extinction of fear.
There is of course some localisation of function in the brain but dynamic interactions between multiple regions produce thought, emotion and behaviour. It's a long step to mapping specific mental illnesses to dysfunction of brain circuits. Insel himself concedes that more research is needed.
Moreover, Insel clearly juxtaposes his concept of mental illness as brain disorder with psychological disorders caused by psychic trauma or conflict. He says we need to rethink our approaches to diagnosis, treatment, and professional training. So he's happy for his approach to encourage psychosurgery and intracranial brain stimulation.
He got an airing of his views in an article, Faulty circuits, for the popular Scientic American. His claim that neuroscience will revolutionise psychiatry is no different from the one made by modern psychiatry since its origins with the asylums. How many more blind alleys will psychiatric research lead us down? Faulty brain circuits in mental illness are as much of a myth as biochemical imbalances.