Default Mode Network
Category: Sleep Science
The Discovery of the DMN and Its Component Regions
The default mode network (DMN) is a functional brain network named by Marcus Raichle and colleagues in 2001. fMRI studies revealed a set of regions whose activity rises consistently when a person is at rest rather than working on a specific task. The main components are the medial prefrontal cortex (mPFC), the posterior cingulate cortex (PCC), the precuneus, the angular gyrus, and the medial temporal lobe. These regions show a paradoxical pattern: activity falls while a task is being carried out and climbs when nothing in particular is being done. What made the discovery striking is that it overturned the intuitive assumption that a resting brain is an idle one. The DMN matters to anyone thinking about dreams because this cluster appears to sustain the brain's habit of assembling stories on its own, even when almost nothing is coming in from the outside world.
How the DMN Relates to Dream Formation
Brain activity during REM sleep has been reported to overlap in part with the activity pattern of the DMN. Activity in the medial prefrontal cortex and the posterior cingulate cortex in particular is discussed in connection with the way a dream builds a narrative around the dreamer. The DMN is also the neural basis of waking mind wandering and daydreaming, which led researchers to treat idle reverie and sleeping dreams as points on a single continuum. In lucid dreaming experiments, reactivation of the dorsolateral prefrontal cortex has been observed, which does not happen in ordinary dreams. The finding suggests that the metacognition behind noticing "this is a dream" rests on a different neural basis than dreaming itself.
Self-Referential Thought and What Dreams Are About
The core function of the DMN is self-referential processing. Recalling the past, picturing what comes next, guessing at another person's feelings, stitching scattered events back into your own story: all of these are inner work organized around the self. The fact that the dreamer is almost always the protagonist, no matter who else turns up in the dream, is thought to correspond to DMN activity. Because the DMN is also involved in emotional processing, the tendency for emotionally charged events to be drawn into dreams is explained within the same framework. In depression, overactivity of the DMN is known to be associated with rumination, the state in which the same thought will not leave you, and that link is a useful reference point for thinking about what the mind does overnight.
Putting an Understanding of the DMN to Use
What is known about the DMN can inform the way you work with your own dreams. Differences in DMN activity patterns have been reported in people who practice meditation. Separately, surveys find that people who meditate regularly report lucid dreams more often. These are two distinct findings, and no causal chain in which suppressing the DMN through meditation makes dreams lucid has been established. Dream incubation, deciding before bed on the theme you want to dream about, sometimes works because the DMN also takes part in goal-directed inner simulation. Keeping a dream journal tends to increase the number of dreams you can recall, which is attributed to exercising that same capacity for binding autobiographical memory over and over. Neither is a technique that pays off in a single night; both assume you will build up several weeks of notes and then look back over them.
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