Neuronal networks showing low frequency BOLD signal fluctuations at rest are involved in important ongoing brain functions. In this study, we focused on the DMN because brain regions within this network may be particularly relevant to the origin and experience of mood and psychotic symptoms (Buckner et al., 2008; Williamson 2007; Greicius et al., 2007). In particular, the pattern of DMN abnormalities in acutely ill subjects is interesting to contrast with previous studies of stable outpatients because acute psychopathology may be associated with more pronounced abnormalities in brain activity. Recent findings indicate that the DMN is active when individuals are attendant to internally-focused tasks, and that each node within the network subserves specific functions related to this general role (Buckner et al., 2008). Our findings confirm previous reports that the DMN is a robust feature of brain activity identifiable in every subject. They also confirm our hypothesis that the mPFC is a major locus of shared abnormality in the DMN in schizophrenia and bipolar disorder. Broadly speaking, our results suggest that spontaneous oscillations in large-scale neuronal circuits are abnormal in psychiatric conditions, possibly underlying aspects of psychopathology.
