[Resting state fMRI studies in first episode psychosis patients: a narrative literature review]

A central hypothesis to understand the pathophysiological background of psychosis is the modified and disconnected spontaneous activity between different brain regions. Studying patients experiencing first episode psychosis (FEP) is important, because the effects of long-term drug therapy and chronic disease processes are smaller and do not interfere with understanding the original brain processes. Resting state functional magnetic resonance imaging (rs-fMRI) provides a detailed working picture of the macroscopic connectivity structures of the brain. Furthermore, it is instrumental for understanding the biological processes of psychoses, and may have a role in the diagnosis. Studies to date provide evidence that disruption of brain networks is a fundamental factor in the development of psychosis.

The aim of our study is to review the literature, with a particular focus on how rs-fMRI can be used to understand early psychosis as a neurodevelopmental disorder. In this narrative literature review, we used the search terms "first episode psychosis" and "resting state fMRI", and focused on the newer English language publications. Based on the search results, the studies were divided into two broad groups. First, we summarise the methods used to study functional connectivity. In the second half of the article, we discuss the analytical techniques that investigate regional brain activity.

FEP is characterized by decreased local network connectivity, while increase of global network connectivity is also observable. The majority of the papers have demonstrated the role of frontotemporal connections and thalamus. Studies examining regional homogeneity also support frontostriatal changes. Decreased activity has been measured in the ventromedial prefrontal cortex and dorsolateral prefrontal cortex. Several studies have described increased activity in the striatum and putamen. In addition, there has recently been an increasing focus on the cerebellum. Most studies have found hyperconnectivity between the cerebellum and the prefrontal cortex, the praecuneus and temporal regions, and in the cerebellar-thalamic-cortical circuit.

The reviewed studies support that rs-fMRI is an important tool in investigating FEP. However, the results are very heterogeneous, as a consequence of the different methods and analysis techniques. In the future, standardized protocols should help data collection and analysis to reduce heterogeneity.