SP 1

The neurobiology of delusions: linking perceptual inference and dopamine

This project investigates the neurobiological bases of delusions, a symptom of certain mental diseases such as schizophrenia. Delusions are beliefs that are not supported by evidence, but are nonetheless held with strong conviction. They can cause great suffering to the affected persons and their environment. For example, affected persons frequently experience intense fear because they feel persecuted and observed, although outside observers cannot find any indication of such a threat. There is convincing scientific evidence that delusions are associated with excessive signalling of the neurotransmitter dopamine, but it is not well understood how such an excess in dopamine signalling might lead to the formation of delusions. Influential theories postulate that alterations in the brain's inferencing machinery that controls perception might be involved.  They assume that expected and insignificant stimuli are automatically perceived as surprising and significant. However, the role of dopamine in such perceptual inference has remained unclear. Therefore, the current project is aimed at establishing an empirical link between dopamine, visual perception and delusions.

Figure 1: Aim of the project. Dopamine is a neurotransmitter that plays an important role in the communication between nerve cells in the brain.  An excess in dopamine has been associated with delusions, a symptom of schizophrenia in which an unfounded conviction is firmly held (e.g. the conviction that one is being persecuted). It is not well understood how a neurotransmitter excess can cause unfounded convictions. The current project is aimed at making a significant contribution to bridging this explanatory gap.

To this end, we will conduct behavioral and functional imaging experiments in individuals with schizophrenia and healthy participants. By the use of mathematical models we will then quantify the mechanisms underlying perceptual inference (in cooperation with project 4). We will test whether these inferential mechanisms are altered in delusions or can be influenced by drugs that stimulate or inhibit dopamine signalling in the brain. The obtained results will be put into context with the findings of ongoing animal research (in cooperation with project 3). If successful, this project will contribute to an understanding of the role of dopamine in perceptual processes that are compromised in delusions.

Figure 2: Applied methods. Participants with and without schizophrenia undergo a perception experiment. With mathematical models we will test which perceptual mechanisms are compromised in delusions. By the use of functional imaging the involved brain regions will be identified.


Keywords: Schizophrenia, dopamine, perceptual inference