Current status of EEG microstate in psychiatric disorders: a systematic review and meta-analysis.

Background: EEG microstates are promising biomarkers for psychiatric conditions, though prior meta-analyses mainly focused on schizophrenia and mood disorders. This study expands the analysis to a wider range of mental disorders, examining microstate variations across the psychosis and mood spectra and assessing medication effects on schizophrenia.

Methods: Following PRISMA guidelines, we conducted a comprehensive literature search, identifying 24 studies meeting inclusion criteria. Analyses were performed across two psychiatric subgroups: psychotic disorders and mood disorders. We further conducted a subgroup analysis within the schizophrenia spectrum to examine differences in microstate properties between medicated and unmedicated patients.

Results: Microstate C demonstrated significant increase in coverage, and occurrence in patients with schizophrenia, first episode psychosis and high risk for psychosis, and increased duration in schizophrenia. The absence of increased occurrence in medicated schizophrenia patients suggests that this feature may be state-dependent or modulated by treatment. In contrast, microstate D exhibited significant decreases in duration and coverage in unmedicated schizophrenia patients, indicating potential links with acute psychotic states.

Conclusions: Our findings suggest that microstates C and D could serve as potential biomarkers in schizophrenia, with microstate D alterations linked to acute psychotic symptoms and microstate C potentially reflecting a chronic course or treatment effects. These results emphasize the clinical potential of microstate analysis in psychotic disorder diagnosis and treatment monitoring. The literature on microstate variations in neurodevelopmental and mood disorders is limited, highlighting the need for further research to determine their biomarker potential in these conditions.