Vocabulary of Mental Disorders: The RDoC Perspective
Classification of mental disorders is extremely complicated. This is because mental disorders, unlike other medical illnesses and diseases, don’t have a clear “cause” . Here is a simple example: we know that COVID-19 is caused due to exposure to a specific virus, but we can’t say the same for a disorder like depression, which probably has a variety of biological or psychosocial causes. Hence, the current method of diagnosis of mental disorders, through popular tools like the DSM (Diagnostic and Statistical Manual of Mental Disorders) and ICD (International Classification of Diseases), is largely symptom-based. Even though this current method of classification is easy to use for clinicians, it has some drawbacks.
The ICD 10, developed by the WHO, and DSM V, developed by the American Psychiatric Association, are currently the most commonly used tools to classify mental disorders. These tools allow clinicians worldwide to have a common understanding of these disorders and, hence, facilitate developments in their screening, diagnosis, and treatments . One assumption that underlies this kind of a classification system is that mental disorders are discrete categories. This assumption gives rise to certain problems that the current diagnostic tools aren't able to clearly address:
Distinction between the “normal” and the “pathological”  - The assumption that mental disorders are categorical implies that there is a boundary that separates people who have the disorder and people who don’t. For instance, in the DSM V, diagnosis involves assessing whether a person has the minimum number of symptoms required to have the disorder. But what if a person misses this cut-off point by just one symptom? This distinction between the “normal” and “pathological” can affect the way these disorders are studied, and hence the way they are treated.
The problem of heterogeneity  - The current methods of diagnosis allow for people who show a variety of symptoms to be diagnosed with the same disorder. This means that two people with the same diagnosis can possibly have few symptoms in common. This raises the question of what binds such cases together.
The problem of comorbidity  - Comorbidity refers to the co-occurrence of two different disorders, something that happens more often than not with mental illnesses. This raises the question of whether there are underlying factors that lead to certain disorders to co-occur, something which is difficult to examine when the disorders are conceptualized as distinct entities.
In 2009, as a response to the several issues with the current conceptualization of mental disorders, researchers at NIMH (National Institute of Mental Health) launched the RDoC (Research Domain Criteria) project . RDoC is a research framework that aims to move beyond symptoms and conceptualize mental disorders in terms of various domains of functioning. In RDoC’s current iteration, they have identified six different “Domains” including Cognitive Systems, Social Processes, and Sensorimotor Systems. These domains are further broken down into “Constructs” and “Subconstructs”, which are meant to capture all the different aspects of a person’s mental functioning. Through this framework, mental disorders are conceptualized as dysfunctions in the different constructs, with functioning ranging from normal to abnormal. For example, from an RDoC perspective, the sleep disturbances present in different disorders could be a result of various levels of disruption in the construct “Circadian Rhythm” under the domain “Arousal and Regulatory Systems”. Furthermore, this disruption in the circadian rhythm can be captured from several different neurobiological and behavioral perspectives, referred to as the “Units of Analysis” in RDoC. For instance, functionality of the circadian rhythm can be assessed by looking at the chemicals in the brain (eg., melatonin), the physiology (eg., brain activity), behavioral patterns (eg., sleeping patterns), or self-reported measures (eg., sleep diary).
The holistic approach encouraged by the RDoC framework can help us gain a better understanding of disorders that have largely been understood based on their symptoms. In addition, RDoC’s dimensional approach tackles the issues identified earlier with the DSM and ICD, because it eliminates the need to create boundaries between disorders. The drawback, however, is that RDoC is not a diagnostic system, but rather a research tool aimed at informing future diagnostic systems. Hence, it will take a lot more time and effort to find ways to translate this research into something that clinicians can use.
With an aim to further unpack ICD 10 and DSM V in the context of RDoC, BrainSightAI is hosting a MasterClass for clinicians on 28th Aug at 5:30 pm. Please register here: https://forms.gle/cACNV3h58Ak6rgHN9