The importance of prediction in delusion formation

Looking at recent structural magnetic resonance imaging (MRI) and functional MRI studies as well as dopamine research and lessons from learning theory, Huber et al summarised the current evidence and hypothesised that delusions should be regarded as aberrant prediction processes (Huber Reference Huber, Schwitzer, Kirchle, Riederer, Laux and Nagatsu2020). What does this mean and how does it happen? There is evidence that an excess of dopamine in specific cortical networks contributes to abnormal salience attribution, which is considered to be the basis of delusion formation. This means that when interpreting sensory input, patients focus on unlikely rather than likely explanations for their experiences, thus making errors of probabilistic reasoning, or prediction errors. We all learn by making constant predictions about our environment. One could argue that in terms of learning we should rephrase Descartes’ famous quote ‘cogito ergo sum’ (I think, therefore I am) as ‘Cogito, ergo praedico’ (I think, therefore I predict). These predictions are constantly tested and aligned with reality. In this process we correct prediction errors, which allows learning. Delusions are maintained when false predictions are not corrected.

Communication problems with patients who have delusions

Various models have been proposed regarding the best approach for patients with delusional infestation. These must take into account clinical, ethical and philosophical aspects. The limited available evidence for clinical approaches favours joint clinics between dermatologists or other specialists and psychiatrists. The ethical considerations are primarily with regard to gradual disclosures of diagnosis in order to optimise outcomes. This is particularly important in this patient group because the patient's high delusional intensity often causes a lack of capacity to make decisions about treatment. However, practical considerations such as patients’ access to their clinic letters require a diagnosis. Some authors have advocated the use of neutral terms like ‘unexplained dermopathy’. Other authors have been more sceptical and prefer the use of a variety of explanatory models in conversation with patients (Freudenmann Reference Freudenmann and Lepping2009; Pearson Reference Pearson, Selby and Katz2012; Lepping Reference Lepping, Huber and Freudenmann2015; Patel Reference Patel and Koo2015). Either way, although it can be ethically acceptable to use principles of gradual or limited disclosure in the patient's best interest (Ryan Reference Ryan, Moore and Patfield1995), if the patient lacks capacity, any such approaches obviously have to be in keeping with national medical council guidelines.

Relevance of Jürgen Habermas

Arguably, the most interesting aspect of communication is the philosophical one. It is important for the clinician to understand why a rational argument with their patient is so difficult. This answer should go much beyond a simple notion stating that the patient holds a false belief. Many philosophers have emphasised the importance of language for communication, but it was Jürgen Habermas who described ‘communicative rationality’. He proposed that for successful communication, four basic principles have to apply in order to achieve successful and rational conflict resolution (Habermas Reference Habermas and Hohengarten1992; West Reference West2020):

• • communication needs to intelligible, in other words it needs to consist of actual words and follow rules of grammar

• • both people need to accept beforehand that whatever they are going to talk about is a legitimate conversation to have

• • there has to be an understanding that both people believe whatever they are saying, and neither is merely trying to manipulate the other one

• • whatever reasoning is used in the conversation, it needs to correspond with certain values and norms that both people agree on and understand.

Language is therefore not a disinterested building block: to communicate anything at all to another person we have to imbed our speech in normative constraints (West Reference West2020). Communicative rationality assumes that as human beings we can get together and make rational decisions starting from a premise of similar values. In doctor–patient relationships this means that people can come together and have a conversation following the four principles set out by Habermas in order to come to a decision they can both agree on about how to move forward. Coming to an agreement normally implies tolerance for the other person's views and a pragmatic analysis. Looking in that way at the conversation with a person who is deluded, we can understand the fundamental problem that may ensue: the patient does not accept that the conversation is a legitimate conversation to have because, as far as they are concerned, they already know what goes on but may need to persuade the clinician of their view. This usually includes an unwillingness to look at the possibility that an alternative explanation exists, other than the one offered by the patient. In other words, even though the patient may truthfully believe their version of the truth to be true, clinicians may struggle to come to a common understanding with the patient by rational discourse. Habermas would argue that any mutual understanding is achieved on the basis of the shared presupposition that any validity claim agreed on can be justified, if necessary, by the use of reason (rational discourse). This is where problems often arise with a person who is suffering from a delusion, as their claim or belief cannot be justified by rational argument accepted by both parties.

The only solution is to accept pragmatically that a rational discourse, or as Habermas would put it, the use of communicative rationality, is not likely to lead to a conclusion. Clinicians are therefore left to either agree to disagree with a patient or to appeal to their tolerance for the other's point of view. They would agree to disagree in order to circumvent the problem of the legitimate conversation that Habermas pointed out. This is often the strategy used by psychiatrists to gain the trust of and ultimately engage the patient.

Other authors have used different approaches to explore ways of dealing with delusions and the communicative aspects of delusion to explain the communication difficulties with deluded patients, for example the pre-reflective abnormal self-awareness model (Gallagher Reference Gallagher and Varela2003).

Practical applications

In practical terms, the clinician may actively invite the patient to trust that they have seen multiple other patients with similar problems before and have successfully treated them. Clinicians may appeal to associated symptoms such as agitation or anxiety, which can be treated with antipsychotics, or they may point out the fact that the patient has nothing to lose by trying a medication against what they perceive to be their better judgement. The philosophical contemplation allows us to see the difficulty in the communication and highlights how normal strategies of transparency and patient cooperation have to be adapted for this particular patient group.