The twenty-first century has witnessed unprecedented scientific advances in areas such as genetics, cognitive neuroscience and biology. These advances, however, have not been accompanied by an improvement in the treatment or diagnosis of mental disorders. For example, leaving aside their limited effectiveness, newer antidepressants were only approved at the beginning of this century. What might have caused this disconnect between scientific advances and treatment? Many argue that it is related to the very definition of mental illness.

Psychiatry has predominantly tended to assign "labels" (disorders) based on the joint presentation of symptoms that are agreed upon by experts and are reflected in diagnostic manuals, among which the best known is the DSM (now in its fifth edition) published by the American Academy of Psychiatry. These manuals, by providing a common language for professionals, have allowed clinical trials to be reasonably independent of the doctors who design them.

However, this approach has also received much criticism regarding the validity of diagnostic labels. Take for example the fact that these labels do not recognize that the boundaries between disorders are often unclear. The occurrence of delusions or hallucinations in severe cases of depression is well known, while a lack of motivation, which is most typical of depression, is also a characteristic symptom of schizophrenia. Other medical specialties have overcome these limitations and, by discovering the root causes of diseases, have displaced diagnosis based solely on clinical symptoms. Indeed, recognizing symptoms only occasionally leads to choosing the most effective treatment.

In 2013, the National Institute of Mental Health in the United States suggested that it was time to investigate alternatives to replace existing classifications of mental illnesses. To do so, researchers proposed a new research framework entitled, "Research Domain Criteria" (RDoC). The RDoC framework assumes that mental illnesses are brain dysfunctions in biological systems relevant for adaptation, such as neural circuits responsible for processing rewards and threats. It also presupposes that such dysfunctions are manifested in markers that can be objectively evaluated. Examples of these potential markers include genetic analysis of biological samples (markers in blood, cerebrospinal fluid, etc.) or neuroimaging. It is thought that the results in these markers have the potential to allow for the grouping of patients in new and more accurate categories, which would lead to more effective treatments to the extent that they would try to modify biologically relevant mechanisms.

Our studies with the University of Cambridge show that there are indeed biological dimensions that go beyond current diagnostic labels, and that may be useful for distinguishing between groups of patients. In particular, we have shown that it is more common to find a reduced brain response in specific areas associated with rewards' processing systems when one expects to receive a positive stimulus in patients with both schizophrenia and depression, supporting the concept proposed in RDoC.

In any case, RDoc also has limitations that cannot be ignored. One applied critique refers to the fact that the measures proposed (genetic and neuroimaging analysis) are perhaps not yet sufficiently developed for reliable and clinically relevant results. A more central issue refers to emphasizing biological aspects of mental illness, forgetting other essential aspects. Epistemology is the branch of philosophy that deals with the nature of knowledge; German Berrios, an epistemology professor of psychiatry at the University of Cambridge, argues that psychiatry, since it seeks to treat diseases of the mind, is a mixed and interdisciplinary discipline, rooted in both the experimental sciences and the social sciences and humanities. Its object of study is, therefore, hybrid and includes both biological and cognitive aspects that cannot be understood apart from essential human elements such as the will, emotion and cognition. On the continuum of mind research and brain research, the RDoC's object of study is unbalanced.

In short, the U.S. government has bet on RDoC, which will have a central role in research on mental illnesses in the coming years. It has almost insurmountable epistemological and methodological limitations that hinder its goal of reconfiguring existing diagnostic classifications. However, it also has positive new aspects, and we predict that it will provide knowledge that will enable us, in the medium term, to better treat people with psychiatric disorders.