The posterior cingulate cortex (PCC), a core region of the default mode network (DMN), shows distinct roles in attention depending on its dorsal and ventral parts. Using fMRI during a working-memory task, standard subtraction analysis showed overall deactivation with increasing difficulty. However, dual-regression functional connectivity revealed a dissociation: the ventral PCC reduced integration with the DMN and anticorrelation with the cognitive control network (CCN) as task demands rose, while the dorsal PCC increased DMN integration and anticorrelation with the CCN. At rest, the dorsal PCC connected with both DMN and attentional networks. These results indicate the PCC supports internally directed thought at low demands and that the dorsal PCC modulates dynamic interactions between networks for attention allocation.
Psilocybin, a classic psychedelic, increases functional connectivity between the default-mode network (DMN) and task-positive network (TPN), reducing the normal orthogonality between these networks. In 15 healthy volunteers, intravenous psilocybin (vs placebo) during resting-state fMRI scans led to greater DMN-TPN connectivity, a pattern also seen in psychosis and meditative states. Thalamocortical connectivity remained unchanged, suggesting it relates to arousal rather than the separateness of internal versus external focus. The findings support psilocybin as a model for early psychosis, where compromised DMN-TPN orthogonality may explain phenomenological overlaps.
Psilocybin, a classic psychedelic drug, may enhance the vividness and visual imagery of positive autobiographical memories. In a small study of ten healthy participants, functional magnetic resonance imaging scans showed that under psilocybin, compared to placebo, recollection of positive memories produced additional visual and sensory cortical activations in the late phase of recall. Participants also rated memories as more vivid and visually rich after psilocybin, and higher vividness correlated with greater subjective wellbeing at follow-up. These findings suggest psilocybin could be useful in psychotherapy for facilitating recall of salient memories or reversing negative cognitive biases.
During an attentionally demanding task, brain activity becomes more synchronized and less variable over time compared to rest. This shift is linked to increased activity in the frontoparietal control/dorsal attention network and decreased activity in the default mode network. A computational model confirmed that activating the frontoparietal network increases synchrony and reduces variability, while activating the default mode network does the opposite. The balance between these networks may control how the brain shifts between an unfocused, exploratory state with high variability and a focused, constrained state with low variability.