Dr. Bruce Cuthbert
Currently, mental disorders are defined by clusters of signs and symptoms, some of which are hundreds or even thousands of years old. Although plenty of information now exists on the biological basis of behavior, no classification
exists that makes use of this information.
NIMH, however, is working on a project called the Research Domain Criteria (RDoC) project
with the goal of providing a framework for classifying research subjects based on genomics,
clinical science and neuroscience. Dr. Bruce Cuthbert, director of NIMH’s Division of Adult Translational Research, discussed RDoC recently at the Association for Psychological Science annual convention in Boston.
“To me, the brain is a motivational computing
machine,” he said. Particular motivational
brain systems control dimensions for the direction and vigor of behavior. In a healthy person, these dimensions of behavior are within
a normal range. In mental disorders, however, extremes in these dimensions occur. For example,
fear is a normal adaptive emotion, but when fear is taken to an extreme, anxiety disorders such as phobias result. Thus, understanding how the brain works by studying its biological aspects such as brain circuits and genetics can help elucidate a classification system for mental disorders.
Cuthbert made clear that this classification system
is only meant to be used for classifying subjects in research studies. The project is not designed to change or replace the Diagnostic and Statistical Manual of Mental Disorders (DSM) or the International Classification of Diseases and Related Health Problems (ICD), the two systems currently used for classifying mental disorders. Perhaps it will influence the criteria for classification
used in these systems in the future; however, the purpose of RDoC is solely to improve research.
RDoC’s approach to classification might contribute
to a solution for many research problems. For example, research has found that there is a genetic relationship between schizophrenia and bipolar disorder. Although they do not appear to be the same disorder, they do not appear to be completely
unrelated either. However, due to the lack of a developed classification system, these disorders are classified as two completely separate ailments in research studies.
“How do we come up with some system of classifying
these patients?” Cuthbert wondered. To offer a suggestion on how to answer this question,
he cited recent research on schizophrenia. This research found that people with schizophrenia
or related symptoms can be divided into three clusters based on the symptoms present and that a different gene was associated with each of these symptom clusters. Future research on the relationship
of these genes to bipolar disorder might make the relationship between schizophrenia and bipolar disorder clearer. A better classification system
could then be developed based on the underlying
Encouraging future research is, in fact, a goal of the project. “We’re trying to encourage basic research that would help us understand these [biological] mechanisms better,” Cuthbert explained. Such research would affect the way scientists
think about disorders.
The RDoC committee plans to hold multiple conferences
to discuss the classification system over the next couple of years, with its first conference this summer.