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Default-mode activity during a passive sensory task: uncoupled from deactivation but impacting activation
Michael D Greicius1, Vinod Menon
1Department of Neurology, Stanford University School of Medicine, CA 94301-5719, USA. greicius@stanford.edu
Journal of Cognitive Neuroscience
|December 17, 2004
Summary
The default-mode network (DMN) is often undetectable with standard analysis during tasks. Independent component analysis reveals the DMN persists even during stimuli, suggesting tasks may not always engage subjects sufficiently.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
Background:
- The default-mode network (DMN) comprises brain regions active during rest.
- These regions, including the posterior cingulate cortex and medial prefrontal cortex, are typically deactivated during high-demand tasks.
- The DMN's role in cognitive processing and its detection using standard methods are subjects of ongoing research.
Purpose of the Study:
- To investigate the detectability of the DMN using standard deactivation analysis versus independent component analysis (ICA) during a passive sensory task.
- To determine if the DMN persists during task epochs and its relationship with task engagement.
- To explore the DMN's potential involvement in episodic memory.
Main Methods:
- A passive, block-design sensory task was employed.
- Standard deactivation analysis (rest vs. stimulus epochs) was compared with ICA.
- Time-series analysis was used to assess DMN activity fluctuations.
Main Results:
- The DMN was undetectable or only partially detectable with standard analysis.
- ICA successfully detected the full DMN, revealing its persistence across rest and stimulus epochs in most subjects.
- DMN activity was uncoupled from the task waveform, remaining largely undetectable as deactivation.
- The hippocampus was confirmed as part of the DMN, supporting its role in episodic memory.
- Greater correlation of DMN activity with rest epochs (i.e., deactivation during stimuli) correlated with higher activation to external stimuli.
Conclusions:
- Standard deactivation analysis may fail to detect the DMN during tasks that are not sufficiently challenging.
- ICA is a more robust method for identifying the DMN and its persistent activity.
- The DMN's activity can persist irrespective of external tasks, suggesting continuous internally generated cognitive processes.
- The degree of DMN deactivation during a task can indicate task engagement and its sufficiency in interrupting internally directed thought processes, potentially involving episodic memory.