1 EEG microstates and the schizophrenia spectrum: evidence for compensation mechanisms Janir Ramos da Cruz 1,2 *, Ophélie Favrod 1 , Maya Roinishvili 3,4 , Eka Chkonia 4,5 , Andreas Brand 1 , Christine Mohr 6 , Patrícia Figueiredo 2 , and Michael H. Herzog 1 1 Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland 2 Institute for Systems and Robotics – Lisbon (LARSys) and Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Portugal 3 Laboratory of Vision Physiology, Beritashvili Centre of Experimental Biomedicine, Tbilisi, Georgia 4 Institute of Cognitive Neurosciences, Free University of Tbilisi, Tbilisi, Georgia 5 Department of Psychiatry, Tbilisi State Medical University, Tbilisi, Georgia 6 Faculté des Sciences Sociales et Politiques, Institut de Psychologie, Bâtiment Geopolis, Lausanne, Switzerland Introduction Electroencephalogram (EEG) microstates are on-going scalp potential configurations that remain stable for around 80 ms (1). Four recurrent and dominant classes of microstates (labeled A-D) are observed in resting-state EEG, explaining around 65-84 % of the global variance of the data (2). Several studies have reported abnormalities in the dynamics of EEG microstates in schizophrenia patients (3). Similar abnormalities have also been observed in adolescents with 22q11.2 deletion syndrome, a population that has a 30% risk of developing psychosis (4). These results prompted researchers to suggest that the abnormal dynamics of EEG microstates is a potential endophenotype for schizophrenia. For endophenotypes, it is important that unaffected relatives also show the abnormal dynamics (5). To the best of our knowledge, no study analyzed the resting dynamics of these four EEG microstate classes in relatives of schizophrenia patients. Methods We examined 5 minutes resting-state EEG data of 260 participants collected across experiments, and we estimated the dynamics of the four canonical EEG microstates using Cartool (6). In experiment 1, to investigate whether unaffected siblings of schizophrenia patients show EEG microstates abnormalities, we tested 38 unaffected siblings of schizophrenia patients, 89 schizophrenia patients, and 69 healthy controls. In experiment 2, to assess whether these abnormalities are also present in people with high schizotypal traits, we tested 42 healthy students scoring either high (n=22) or low (n=20) in schizotypal traits. In experiment 3, to investigate