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.
A novel imaging technique called molecular connectivity (MC) combines functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) to map how specific molecules, such as the serotonin transporter, interact across brain regions. Using dynamic [11C]DASB PET scans in rats, the study examined changes in serotonin transporter distribution after a single dose of MDMA (ecstasy). Results showed clear alterations in molecular connectivity following MDMA, directly linking drug effects on serotonin transporter occupancy to changes in functional brain networks. This approach provides a comprehensive view of brain function at the molecular level and offers new ways to understand how drugs modulate brain activity.
During nonrapid eye movement (NREM) sleep, consciousness fades as the brain's dynamic functional connectivity changes. Using simultaneous EEG-fMRI recordings in 12 healthy men, the study examined two aspects of dynamic connectivity: mean (dFCmean), reflecting stable network integrity, and variance (dFCvar), indicating instability of information transfer. As sleep deepened, dFCmean decreased progressively across waking and NREM stages (N0~N1 > N2 > N3), while dFCvar peaked during N2 stage (N0~N1 < N3 < N2), suggesting unstable whole-brain synchronizations. In N3 stage, overall network integration was disrupted, with lowest dFCmean and elevated dFCvar. The findings suggest that consciousness dissipates when network specificity breaks down alongside increasing variability of information exchange.
Communication between different brain systems is essential for complex functions. Using resting-state fMRI and a technique called physiophysiological interaction, the authors found that the salience network may modulate the relationship between the default mode network and executive networks. The basal ganglia and thalamus positively interacted with the salience and dorsal attention networks, while negatively interacting with the salience network and default mode network. These results reveal complex, modulatory interactions among brain networks during rest.