The New York Times has an insightful article on the utility of brain scans for helping and treating people with mental illness.
Mental illness is diagnosed on the basis of a clinical interview, where the clinician interviews the patient and encourages them to explain aspects of their first-person experience.
This means that the criteria for diagnosis, although internationally agreed upon, are subjective – in that it is the clinician who decides whether they are present or not.
For example, the DSM criteria for clinical depression include items such as depressed mood, loss of pleasure, feelings of guilt and low self-esteem. None of these can be measured objectively.
When brain scans arrived, particularly those that measured brain function, it was hoped that there would finally be an objective test for many mental disorders based on the biology of the brain.
There has been some success in finding biological differences between the brains of healthy and diagnosed individuals. The problem is that these differences are not reliably diagnostic.
For example, when a group of people with depression and without depression are compared, reliable differences in brain function can be found. However, this only reflects the fact that individuals with the diagnosis are more likely to show the difference, but there are also individuals with the diagnosis who do not have the same differences.
This also ignores the fact that the diagnosis and definition of mental illness are often culturally influenced. The fact that homosexuality was classified as a mental disorder by the American Psychiatric Association until 1973 is a notorious example.
Another complication is that there is often an element of subjective decision making in analysing brain scans – to produce the familiar ‘brain images’ we are used to seeing.
The media often miss many of these subtleties, portraying brain scans as more impressive than many scientists give them credit for.
The New York Times article, therefore, does an admirable job of tackling some of these issues and outlining the promises and pitfalls of the neuroscience of mental disorder.
This comes at a time when psychiatry is looking beyond the current diagnostic manuals as the sole definition of mental disorder, and considering the concept of the ‘endophenotype‘ – measurable aspects of biology thought to be the key underlying components that increase risk for mental disorder.