Information processing and expectations in delusion-proneness

Abstract

One of the most characteristic features of psychosis is delusional ideation. Delusions represent incorrect and inflexible beliefs that are not based on reality. It has been proposed that delusions may be secondary to impairments in reality monitoring. These systems are formalised in a predictive coding framework, building on Bayesian inference theory, that describes the brain as an inference machine. In this framework, information processing is conceptualised as a multi-level pyramidal system that shows an increasing level of integration. The bottom levels (including primary sensory cortex) process simple sensory input while higher levels are associated with information processing of increasing complexity.

It has been suggested that in psychosis aberrant salience attribution leads to deficits in the lower levels of this hierarchical system, which in turn result in abnormal sensory experiences. Moreover, it has been proposed that delusions are formed in order to make sense of these unusual experiences that cannot be explained with normal logic. Overly inflexible beliefs and delusions are not solely manifest in psychotic patients. They are also present, to a lesser degree, in the general population. For example, they are represented in a personality trait referred to as delusion-proneness. In the work presented in this thesis, we decided to study delusion-proneness in a healthy population in order to better understand the mechanisms underlying this trait.

Using different paradigms tackling self-recognition, decision making processes, and fear learning we confirmed that delusion-prone individuals show behavioural impairments similar (but attenuated) to psychotic patients. Taken together, our results bring support to the idea that delusion-proneness shows a double dissociation in the information processing hierarchy, with high-level prediction systems exerting an overly strong influence over imprecise lower-level prediction systems. While delusion-prone individuals show difficulties in generating low-level expectation signals, they tend to integrate more readily higher-order signals (i.e. beliefs) and overly rely on them in order to understand their environment.

Our work also points towards an involvement of frontal brain regions, more precisely lateral orbito-frontal cortex (lOfc), in the processing of high-order input in delusion-proneness. Specifically, we found a larger effect of instructions on fear learning in delusion-prone individuals than in controls, which was associated with a stronger connectivity between lOfc and brain regions involved in fear and pain processing. Our results also suggest trait co-morbidities between delusion-proneness and sub-clinical symptoms of Attention Deficit and Hyperactivity Disorders (ADHD), as well as Autism Spectrum Disorders (ASD). This argues for a better assessment of these traits in studies focusing on psychosis-related states. While the results presented in this thesis need to be replicated and investigated in a clinical population, our studies have helped advance the understanding the mechanisms underlying delusion-proneness.