The default mode network (DMN), which is most active when the mind is at rest, is often treated as a single system, but its two main hubs—the ventromedial prefrontal cortex (vmPFC) and the posterior cingulate cortex (PCC)—interact with different task-focused brain networks. Using resting-state fMRI and a seed correlation approach, activity in vmPFC negatively predicted activity in networks for visual spatial and temporal attention, while activity in PCC negatively predicted activity in motor control circuits. Granger causality analyses indicated that vmPFC and PCC exert greater influence on their anticorrelated networks than the reverse, suggesting these DMN nodes may directly modulate task-positive networks. The DMN is thus more heterogeneous than commonly appreciated.
Self-generated thoughts—such as daydreaming or mind-wandering—are linked to distinct patterns of spontaneous brain activity. Using the New York Cognition Questionnaire (NYC-Q) and resting-state fMRI data from the Nathan Kline Rockland Enhanced sample, researchers found that thoughts cluster into dimensions of content (future-related, past-related, positive, negative, social) and form (words, images, specificity). Individuals who reported more imagery showed greater low-frequency fluctuations in perigenual cingulate cortex, part of the default-mode network. Those with more future-oriented thoughts showed less homogeneous neural fluctuations in lateral occipital cortex, suggesting decoupling from sensory processing. Self-generated thought is a heterogeneous category, and studying its content helps understand brain dynamics.