Understanding mental illness by mapping mind-brain relationships
Our consortium has posted several articles on this website dealing with the complex issue of what we mean when we talk about a brain disease. Once again we have discussed this topic in the wake of an important National Institutes of Mental Health (NIMH) initiative. Here is our take on the history of this most recent attempt to grapple with sorting the varieties of mental disorders.
In the 19 March 2010 issue of Science Greg Miller published a position paper describing the focus of the NIMH initiative entitled Beyond DSM: Seeking a brain-based classification of mental illness. In one page he does an excellent job summarizing the NIMH plans for developing a Research Domain Criteria (RDoC), neurobiological (brain region or neuochemical signaling pathway specific evidence based classification of forms of mental disorders. The disorders that would be neurobiologically mapped include extreme forms of emotions, cognitive functions and social processes. Coincidentally, a totally different Greg Miller (University of Illinois), a gifted and prolific researcher, captures the essence and spirit of the NIMH initiative by providing a framework for thinking about mind-brain relationships. His paper entitled Mistreating Psychology in the Decades of the Brain (Perspectives on Psychological Science 2010; Vol. 5 (6); 716-743) grapples with issues that are central to adequately defining the relationship between psychology and biology. That Greg Miller takes little for granted in how we think about behavior in a research world dominated by neuroscience thinking.
The DSM (Diagnostic and Statistical Manual of Mental Disorders has been used for decades to classify mental illnesses. The diagnostic categories that are part of DSM are based on symptoms (behavior) rather than causes of a disorder. It has been revised many times and each new attempt falls short of what clinicians find useful. Researchers have been particularly frustrated when using the DSM in research. Frequently DSM diagnostic categories are used as the independent variable and when those categories are vague, inaccurate, unreliable so too are the findings that emerge from studies in which the diagnostic categories are used. After all, when the independent research variables are suspect then the value of even the most objective, reliable and sensitive measures of brain or behavior are compromised.
In July of 2010 Tom Insel, Bruce Cuthbert and colleagues in a commentary contribution to the American Journal of Psychiatry (167:748-751, July 2010)
provide additional details of the NIMH- RDoC initiative. The initiative is based on 3 assumptions: 1) mental illnesses are brain disorders (brain circuit disorders; 2)neuroscience tools can be used to identify the brain circuit disorders; 3)that the proposed RDoC framework can be used to identify brain circuitry-behavior relationships (for functions like fear, reward, executive functions, anxiety, impulse control. While the focus for RDoC is on neural circuitry,levels of analysis from circuitry functioning to genetic and molecular/cellularfactors that ultimately influence such function.
This is an incredibly ambitious initiative that at the very least will provide new insights and knowledge about brain-behavior relationships. It also provides a powerful integration of tools and theory that can be used to better understand the etiology of brain diseases and thereby provide us with better tools for preventing and treating these disorders. Useful results will come slowly and therefore require patience and persistence. It will also require critical thinking about the meaning of any classification system. For example, there are some who would argue whether we should even define mental illness as a brain disease? The notion of a disease in the world of medicine implies that we know something about etiology, the course of the disease and how to treat it. Brain disease does not fit that disease criterion. We will follow the progress of this initiative in future postings.