This study has a modest sample size because we studied acutely ill patients in 3 groups, which presented logistic difficulties. There was a high attrition rate especially in the mania group, and the patients who could not complete the study were somewhat more symptomatic than those who could. Nonetheless, the YMRS score of our manic patients was over 24, indicating that the completer patients were still highly symptomatic. Also, all patients were medicated at scan time in our study and a role for psychotropic medications in our findings cannot be ruled out. Nonetheless, two factors suggest that medication effects were not prominent in our study: both patient groups were on similar medications, but they showed different DMN abnormalities; and there was no relationship between our findings and CPZ equivalents. Another limitation of our study is the diagnostic heterogeneity in the schizophrenia group, where 7 out of 14 subjects were diagnosed with schizoaffective disorder. We cannot rule out the possibility that schizoaffective disorder patients show a differential pattern of DMN abnormalities which we are confounding with schizophrenia, but we do not
