The Default Mode Network and Its Role in Psychedelics

Описание: In this 18-min micro-lecture, Neuroscientist ‪@CedarFrog_SciComm‬ (MS) offers a deep dive into the Default Mode Network (DMN), the brain system that becomes active when our minds wander, daydream, or turn inward.

II. What the Default Mode Network Is
The DMN is a network of brain regions that activates when we’re not focused on a task. It supports internal thinking—like recalling memories, imagining the future, or reflecting on who we are. Discovered accidentally in 2001, the DMN overturned the old idea that the brain “rests” when unfocused. Instead, it revealed a powerful internal mode that works in opposition to attention networks.

III. Core Regions of the DMN
The DMN is anchored by several key hubs:
(1) Medial Prefrontal Cortex (mPFC)
Involved in self‑referential thinking, moral reasoning.
Also, integrating emotion with cognition.
(2) Posterior Cingulate Cortex
DMN's metabolic hub.
Hyperactive in depression; major target of psychedelic therapy
(3) Inferior parietal lobule/angular gyrus
Supports perspective‑taking, mental simulation.
Also, narrative comprehension.
Additional regions—including the hippocampus, precuneus, retrosplenial cortex, and temporoparietal junction—contribute to memory, imagination, empathy, and moral reasoning.

IV. What the DMN Does
Five major cognitive functions supported by the DMN:
(1) Reconstructing personal memories and building a sense of identity
(2) Imagining future scenarios and planning
(3) Reflecting on our feelings, goals, and self‑concept
(4) Understanding others’ thoughts and emotions
(5) Supporting moral reasoning and value‑based decisions
The DMN is the brain’s internal narrative engine—the system that helps us understand who we are across time.

V. How Psychedelics Affect the DMN
Classic psychedelics such as psilocybin, LSD, and DMT bind to serotonin’s 5‑HT2A receptors, triggering serotonin‑like effects on mood, emotional balance, and cognitive flexibility. One of their most consistent neural effects is a reduction in DMN activity and connectivity, especially between the medial prefrontal cortex and posterior cingulate cortex. This temporary quieting of the self‑referential system is linked to:
Ego dissolution.
Reduced rumination.
Emotional release.
Increased openness.
New insights and perspectives.
Different psychedelics influence these networks in distinct ways. Ayahuasca may promote emotional release and shifts in self‑processing, while LSD increases global brain connectivity, allowing regions that rarely communicate to exchange information.

VI. Models Explaining Psychedelic Effects
Hadley introduces several leading theories that attempt to explain how psychedelics reshape brain function:
(1) Relaxed Beliefs Under Psychedelics (REBUS).
Psychedelics loosen rigid belief structures used to interpret the world
Entropic Brain: ↓ neural rigidity & beliefs; ↑ plasticity & new beliefs.
Free-Energy Principle: Brain predicts, updates beliefs with results.
(2) Cortico‑Striatal‑Thalamo‑Cortical (CSTC).
Psychedelics reduce sensory gating in the thalamus.
Allows more sensory information into the cortex.
Contributes to vivid, sensory-rich experiences.
(3) Strong Prior (SP).
Highlights shifts in top‑down vs. bottom‑up processing.
Reduced sensory input & increased reliacne on internal expectations
Explains hallucinations, even in sensory depreivation.
(4) Cortico‑Claustro‑Cortical (CCC).
Psycheelics disrupt communication between the PFC & claustrum.
Loosens higher-order control networks; enables ↑ fluid cognition.
Together, these models help explain why psychedelics can loosen entrenched patterns and support psychological change.

VII. Meditation, Movement, and the DMN
The lecture also highlights how non‑drug practices—such as meditation, yoga, tai chi, and qigong—can modulate the DMN in ways that overlap with psychedelic effects. These practices can decrease DMN activity, strengthen attention networks, reduce mind‑wandering, and support emotional regulation.

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