Nature reviews. Neuroscience
July 5, 2021
Jonathan Smallwood, Boris C. Bernhardt, Robert Leech et al.
970 citations
The default mode network (DMN) is a set of brain regions in the parietal, temporal, and frontal cortex that typically reduce activity during attention-demanding tasks but increase activity during complex cognition linked to memory or abstract thought. These regions are located farthest from sensory and motor systems. The paper considers how knowledge of the DMN's topographic characteristics can be used to better understand its contributions to cognition and behavior.
Nature Communications
August 23, 2019
Adam Turnbull, Hao-ting Wang, Charlotte Murphy et al.
197 citations
When a task is undemanding, people often let their minds wander to personally relevant thoughts. The dorsolateral prefrontal cortex (DLPFC), a brain region known for maintaining goal representations, also helps prioritize off-task thinking. Neural activity in the DLPFC was high both when people were on-task under demanding conditions and off-task during a non-demanding task. Individuals who increased off-task thought when external demands decreased showed weaker correlation between neural signals linked to external tasks and lateral default mode network regions within the DLPFC, and had less cortical grey matter in regions sensitive to those external signals. The findings suggest that humans use the DLPFC to align cognition with personal goals when environmental demands drop, prioritizing daydreaming.
iScience
February 2, 2021
Jonathan Smallwood, Adam Turnbull, Hao-ting Wang et al.
130 citations
The landscape of ongoing thought is heterogeneous and shaped by both personal traits and environmental context. Recent work shows that attention and control systems organize experience in response to changing demands, while the default mode network contributes not only to task-negative or episodic content but also to the vividness of experience in both task contexts and spontaneous self-generated states. Multiple neural systems reflect the landscape of ongoing thought, and it is important to distinguish processes that shape how experience unfolds from those that regulate it.
Neuroimage
April 25, 2022
Manesh Girn, Leor Roseman, Boris C. Bernhardt et al.
112 citations
LSD and psilocybin flatten the brain's normal hierarchical organization, reducing the functional separation between sensory and higher-order networks and increasing cross-talk between them. Analyzing two resting-state fMRI datasets, the principal gradient of cortical connectivity—which normally runs from basic sensory areas to complex association regions—was significantly compressed under both drugs compared to placebo. This flattening was driven by decreased specialization at both ends of the hierarchy: default mode and frontoparietal networks at the top, and somatomotor networks at the bottom. The findings support a proposed mechanistic model of the psychedelic state and demonstrate that macroscale connectivity gradients can be acutely altered by a pharmacological intervention.
Neuroimage
June 22, 2020
Brontë Mckeown, Will Strawson, Hao-ting Wang et al.
102 citations
People whose brain connectivity patterns make the sensorimotor system most distinct from the visual system are more likely to report thoughts about solving problems or goals and less likely to report thoughts about the past. This finding comes from a study where participants underwent resting-state fMRI and then completed a questionnaire about their thoughts during the scan. A non-linear dimension reduction algorithm identified components explaining the greatest variance in whole-brain connectivity patterns. The results suggest that unique patterns of experience are linked to distinct neurocognitive profiles, with unimodal systems playing an important role.
Scientific Reports
December 3, 2020
Theodoros Karapanagiotidis, Diego Vidaurre, Andrew J. Quinn et al.
82 citations
When people are not engaged in an explicit task, they experience a variety of self-generated thoughts, such as planning or reminiscing. Using machine learning to analyze brain activity from resting-state fMRI scans, researchers identified distinct neural states that recur over time. Two of these states predicted different patterns of thinking. One neural state, resembling activity seen during demanding tasks, was linked to problem-solving about the future. Another state, associated with less demanding conditions, was tied to intrusive thoughts about the past. These two states fell at opposite ends of a brain hierarchy related to cognitive demand. The findings show that tracking moment-to-moment changes in brain function can help classify self-generated mental states and that these states align with the brain's response to cognitive tasks.
Nature Neuroscience
January 28, 2025
Casey Paquola, Margaret Garber, Stefan Frässle et al.
58 citations
The default mode network (DMN) is a set of brain regions important for complex thought and behavior. By combining postmortem tissue analysis and brain scans, researchers found that the DMN contains different types of cells, some specialized for processing single senses, others for combining information, and still others for memory. The DMN includes regions that receive input from sensory areas and a core that is relatively cut off from direct sensory information. Analysis of how signals flow through the DMN showed it uniquely balances output across different levels of sensory processing. These findings provide a structural basis for understanding the DMN's broad role in brain function and cognition.
bioRxiv (Cold Spring Harbor Laboratory)
May 3, 2020
Manesh Girn, Leor Roseman, Boris C. Bernhardt et al.
27 citations
preprint
LSD and psilocybin flatten the brain's hierarchical organization, reducing the functional separation between sensory and higher-order cognitive networks. Using a non-linear dimensionality reduction technique on resting-state fMRI data, the authors found that both drugs compressed the principal gradient of cortical connectivity, which normally spans from unimodal (sensory) to transmodal (association) cortex. This flattening was driven by decreased differentiation at both ends of the hierarchy—default and frontoparietal networks at the upper end and somatomotor networks at the lower end—and was accompanied by increased crosstalk between unimodal and transmodal regions. Changes in the principal gradient under LSD tracked self-reported ego-dissolution. The findings support a mechanistic model of the psychedelic state and demonstrate that macroscale connectivity gradients are sensitive to serotonergic modulation.