Altered functional connectivity of the hippocampus in cortico-subcortical networks in early-stage and emerging psychosis

Background: Deficits in the hippocampus are a consistent finding in schizophrenia and have also been demonstrated in early-stage psychosis. Moreover, alterations in hippocampal anatomy and connectivity have been implicated in aberrant functional interactions in subcortical and cortical networks. However, the nature and extent of these alterations and their association with frontal and subcortical regions remain unclear. Methods: To address these questions, we analysed resting state fMRI functional connectivity and graph properties in n = 93 individuals at clinical high-risk for psychosis (CHR-P), n = 26 patients with first-episode psychosis (FEP), n = 31 individuals with affective disorders and substance abuse as well as n = 58 healthy controls. We used novel denoising techniques and individually optimised functional connectivity matrices, which were compared across clinical groups. Finally, the centrality of the hippocampus as well as network segregation and integration were assessed using graph-based analysis. Results: Both the FEP and CHR-P groups were characterised by reduced functional connectivity between the hippocampus and inferior frontal cortex albeit the differences in CHR-P individuals did not survive corrections for multiple comparisons. Compared to CHR-P, FEP show lower centrality of the hippocampus but increased network segregation. Conclusions: Our findings show lower connectivity between the hippocampus and frontal cortex in early-stage psychosis, with FEP patients showing stronger decreases in connectivity compared to CHR-Ps. Furthermore, network-based analyses highlight reduced centrality in FEPs compared to CHR-Ps, indicating reduced influence on the wider network. Thus, altered connectivity along the hippocampal-frontal axis could be a potential marker of illness stage in early-stage psychosis.