The Default Mode Network

Written by Austin Mao. Educational only, not medical advice.

What is the Default Mode Network?

The Default Mode Network (DMN) is a set of interconnected brain regions, primarily the medial prefrontal cortex, posterior cingulate cortex, and angular gyrus, that activate when the mind is at rest and not focused on external tasks. It is the network most associated with self-referential thought: ruminating on the past, projecting into the future, and constructing the narrative of “I.”

Think of it as the radio playing in the background of your mind. Normal DMN activity is useful, it supports self-reflection, social cognition, and planning. The problem emerges when the radio gets stuck on one station: rumination, anxiety loops, or trauma narratives that replay without resolution.

The DMN in mental health

Researchers have linked the DMN to rumination in depression, to anxious future-thinking, and to craving and trauma-related thought loops. The imaging findings are heterogeneous, though: a large multi-site analysis of 1,300 people with major depression and 1,128 controls found reduced, not increased, DMN connectivity in recurrent depression (Yan et al., PNAS 2019). The “radio stuck on one station” picture is a useful metaphor, not a settled finding.

Conventional therapy often attempts to interrupt these loops through cognitive restructuring. This works, but it works slowly, because you are essentially trying to change the narrator while the narrator is still narrating. That is a metaphor, not a measurement.

Psilocybin and reduced DMN integration

Robin Carhart-Harris and colleagues at Imperial College London gave a single intravenous psilocybin infusion to healthy volunteers and found decreased blood flow and BOLD signal in hub regions including the thalamus, anterior and posterior cingulate and medial prefrontal cortex, plus reduced coupling between the medial prefrontal and posterior cingulate cortices (PNAS 2012). That study did not test dose-response. Participants describe the experience subjectively as a dissolution of the boundary between self and world, sometimes called ego dissolution, and a felt sense of belonging to something larger than the individual story.

The mechanism: psilocybin (as psilocin) acts as a 5-HT2A agonist in the prefrontal cortex, disrupting the corticocortical communication that sustains normal DMN activity. Acute fMRI shows reduced network integration, not an “offline” network, and whether the human brain is more plastic during the 4–6 hour acute state has not been demonstrated.

Source: Carhart-Harris RL et al., “Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin,” PNAS, 2012.

What was measured after dosing

In mice, a single psilocybin dose increased dendritic spine density and size by about 10% within 24 hours, and the change persisted at one month (Shao et al., Neuron 2021). In patients with depression, fMRI measured increased global brain integration about three weeks after treatment (Daws et al., Nature Medicine 2022). A rise in BDNF after psilocybin has not been established in humans.

No study has shown that integration practices, IFS parts work, somatic work, journaling work better inside a particular time window, or that integration support lengthens benefits. Ceremonia treats integration as central to its approach as a matter of its own practice, not a research finding.

Other practices that quiet the DMN

Meditation and mindfulness practice have also been studied for effects on DMN activity, with modest and mixed results. No study has compared psilocybin-assisted therapy with meditation training on a time-equivalence basis.