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Brain diseases and psychopathology traps

Denny Borsboom

14.12.2021

Some years ago, I went to get a prescription at a pharmacy. It was on a Sunday, and a considerable line of people had formed in front of the weekend pharmacy, where an employee was handing out prescriptions from behind a counter. While I was waiting, a man behind me loudly complained that he needed his medication and he needed it now. The employee asked him to keep quiet and wait for his turn just like everybody else, upon which he shouted, from the top of his voice “but they don’t have ADHD, like me! I can’t wait for my turn, that’s why I need that medication now!”

It was a striking expression of what clinicians call the disease model of mental disorders. The disease model holds that overt, observable symptoms (e.g., not being able to wait for one’s turn) are attributable to an underlying disorder (in this case, ADHD). Typically, that disorder is seen as a physical condition: a problem in the brain. Indeed, the thesis that mental disorders like depression, phobias, and ADHD are in fact brain diseases is common espoused by influential scientists and organizations. For example, the leadership of the main U.S. authority on the topic, the National Institute for Mental Health (NIMH), stated in an influential Science paper that “as new diagnostics will likely be redefining ‘mental disorders’ as ‘brain circuit disorders’, new therapeutics will likely focus on tuning these circuits”.

The picture is simple and seductive. If you can’t wait for your turn, have persistent low mood, or suffer from gambling disorder, it’s because of a problem in your brain circuit. Yet, few disorders have been successfully related to robust evidence of malfunction in the biological system, and methods for tuning specific brain circuits are far and in between. Classic examples where this has in fact happened, as in the cases of Syphilis and Down syndrome, lie far in the past and in a nontrivial sense no longer are seen as mental disorders at all. Although it is certainly the case that common mental disorders like depression are associated with genetic markers and neurophysiological features, these associations are far too weak and unspecific to bolster the claim that mental disorders are in fact brain circuit disorders. For instance, as Eiko Fried and Rogier Kievit argued in their response to a paper that claimed such associations for the case of depression, if anything the data suggest that “brains of depressed patients are remarkably similar to brains of healthy individuals”. The same holds for most other common mental disorders.

It is interesting that many scientists and laypeople are prone to persist in the idea that disorders are brain diseases despite the lack of evidence for this position. At least in part, that is because people tend to confuse description and explanation. Mental disorders are diagnosed by matching the problems people report to groups of symptoms that are listed in a diagnostic manual, such as the DSM-5. But the diagnosis does not identify anything independent of the symptoms: a label like “ADHD” just is a shorthand for the statement that you have the symptoms listed under that label. As a result, if a person says “I can’t wait for my turn because I have ADHD,” they are actually saying “I can’t wait for my turn because I can’t wait for my turn”. That isn’t much of an explanation, of course.

Second, many people have the intuition that, if their disorder is not a brain disease, then it isn’t real - or even that it’s their fault. A biologically identifiable disease seems to lift this problematic blame. This line of reasoning is invalid, because a wide variety of medical diseases in fact are produced by behavior that is at least to some extent under our control (think of lung cancer and obesitas), and there is a significant number of mental health conditions that are due to behavior not under the person’s control (think of addiction and obsessive-compulsive disorder). So, responsibility and biology really don’t have that much to do with each other.

Getting trapped in a psychopathology network

Nevertheless, thinking of mental disorders as brain diseases is a highly seductive metaphor, and if we want to break the reductionist stalemate, we need a better one. I think a good candidate metaphor is the notion of a psychopathology network. Problems in the area of mental disorders tend to create other problems, so they form networks of mutually reinforcing problems that feed on each other. Although that’s so obvious it’s almost trivial, the consequences of thinking this conception though are not trivial at all. A network of problems can create an attractor state in the system that acts as quicksand: every time you try to get out, you get being pulled back by strong interactions between problems. This leads to a psychopathology trap. I described how this works for the case of Panic Disorder in my previous blog post

Interestingly, the idea of a psychopathology network does not exclude biological causes of symptoms (for instance, a symptom like insomnia can clearly arise from those), and some of the mechanisms supporting these connections between symptoms are also driven by biological functions (e.g., insomnia can produce changes in eating behavior because sleep and appetite both involve the biological clock). However, other symptoms and connections between them involve psychological processes (e.g., the tendency to blame oneself for anything that goes wrong), social factors (e.g., if you lack social interests or skills, your social network may become thin), and cultural contexts (e.g., the consequences of drug use depend in part on whether the drug in question is legal or not). As a result, psychopathology traps are likely to involve biological, psychological, social, and cultural trapdoors (and methods that integrate these levels of analysis are sorely needed). That may in fact be why they are so difficult to understand, predict, and manage.

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