EEG microstates in schizophrenia: a candidate endophenotype

Objective: Electroencephalogram (EEG) microstates are on-going scalp potential configurations that remain stable for around 80 ms. Abnormal temporal dynamics of specific classes of microstates have been suggested as a potential endophenotype for schizophrenia. For an endophenotype, it is important that unaffected relatives of schizophrenia patients also show the abnormal dynamics. To the best of our knowledge, no study analyzed the resting dynamics of EEG microstate in relatives of schizophrenia patients. Methods: Here, we used high-density EEG to study the microstate dynamics in 5 minutes resting-state recordings of 38 unaffected siblings of schizophrenia patients, 89 schizophrenia patients, 69 healthy controls, 42 healthy students scoring either high or low in schizotypal traits, and 22 patients with first episodes of psychosis (FEP). We also tested the FEP patients two more times throughout one year to assess whether the microstates dynamics change with disease progression. Results: Schizophrenia patients showed increased presence of a microstate class labeled C and decreased presence of a microstate class labeled D compared to controls. Siblings showed similar patterns of microstate classes C and D as chronic patients (endophenotype concept). Surprisingly, siblings showed an increased presence of a microstate class labeled B compared to chronic patients. A similar result was also found in students scoring high in schizotypal traits compared to the ones scoring low. No difference was found between FEP and matched chronic patients. Moreover, the microstates dynamics remained stable throughout one year. Conclusions: Our findings suggest that the dynamics of microstate classes C and D meet most of the requirements for an endophenotype for schizophrenia. The novel finding of the increased presence of microstates class B in siblings, as well as students scoring high in schizotypal traits, may reflect a compensation mechanism opposing the vulnerability to develop schizophrenia.