The Default Mode Network (DMN) is the part of your brain that’s in charge when you’re awake, but not focussed on any specific activity. Think of how your mind drifts when you’re brushing your teeth, or when walking a commute you’ve walked countless times. The DMN is a particular network of brain regions that activate when you’re in this idling state/default mode.

The DMN was discovered by accident. When fMRI started to be used for cognitive testing in the 90s, they noticed that a particular brain region was active when participants were in-between tasks. This led to the idea that, rather than the idea that the brain is just resting/doing nothing important between activities, there is actually a coordinated brain network of regions active for the activity of resting. This was then tested and found to be a very consistent aspect of human cognition. Asking participants to engage in tasks like autobiographical memory recall, introspection, imagining the future, thinking of others’ perspectives, generated more activity in the DMN. This led to the conclusion that the DMN, active when we are resting, is a hub for self-reflection, social evaluations, memories, and ‘mental time travel’.

It’s interesting to think that it required neuroimaging to find that out. You’d think we’d have been aware of what our minds were doing in-between tasks, but early neuroscience just thought of this time as ‘idling’ and neuroscientifically uninteresting. Except for Hans Berger, inventor of the encephalogram, who in 1929 proposed that the brain is continuously working even at rest, but his ideas weren’t taken seriously at the time.

Also note the re-emergence of this narrative that the brain is constantly seeking stimulation. When there is none externally, it’s generated internally.

The Clinical Side

Further neuroimaging of the DMN showed that it has a significant relationship with various mental health conditions. It’s been shown that disruption in the DMN is prominent amongst those with Alzheimer’s, correlating with the progression of memory loss and cognitive decline. Interestingly, decreased activity in the DMN is now considered an early biomarker of Alzheimer’s and is a key component of projects involved with early detection (Ereira et al., 2024).

Conversely, hyperactivity in the DMN has been strongly linked to depression, and in particular the rumination aspect of depression (Zhou et al., 2020). In my experience, this feels right. One of the more prominent symptoms of my mental dysregulation has been overthinking/rumination. I believe this is part neurological disposition, and part my DMN becoming a more prominent aspect of my thought as I attempted to think my way out of my feelings. Over the long-term, while I feel I’ve improved at introspecting and interpersonal thinking, at times this overthinking strays into a compulsive rumination, or a maladaptive dwelling. There’s a balance to be found between the two.

Hyperactivity in the DMN is also associated with anxiety disorders (Yuan et al., 2023) although I can speak to this less. Intuitively I can see the connection. Disrupted connectivity in the DMN has also been linked to schizophrenia, in particular symptoms like hallucinations or delusions (Wang et al., 2015).

These trends in the literature make it clear that the DMN strongly influences the flow and tension of our base-level thoughts.

Do Animals Have a DMN?

Interestingly, similar activity in the DMN has been identified in several non-human animals. Monkeys, especially macaques, exhibit similar types of activity in the DMN as humans (Mantini et al., 2011). Even some rodents display simplified versions of our DMN activity (Lu et al., 2012).

The interesting aspect of this is that it implies that animals, particularly more social mammals, have some form of self-directed thought/social cognition/imagination. I wonder what a monkey daydreams about.

The Neuroscience

The DMN is composed of several key regions spread across the brain:

Dorsomedial Prefrontal Cortex – Higher-order cognitive processes like decision making, social cognition, predicting behaviour.

Posterior Cingulate Cortex – Self-awareness, autobiographical memory, modulating attention.

Precuneus – Self-awareness, visuospatial navigation and memory, complex decision-making.

Temporoparietal junction – Integrating sensory information, theory of mind, empathy, moral judgements.

Hippocampus – Formation and retrieval of memory (episodic and declarative).

Meditation and the DMN

Meditation is the enemy of an overactive DMN. The key focus of meditation is a conscious engagement in present-moment awareness, without judgement, and without any sense of task-achievement. This is the opposite of the DMN, which ruminates about the past and future, strives to understand itself and others, and is quite active and goal-oriented.

 Long-term meditators show reduced activity in the DMN, and are much better than new meditators at managing rumination (Brewer et al., 2011). Long-term meditators show increased gray matter in the brain compared to controls, although remarkably it’s been shown that 8-weeks of meditation practice is enough to generate significant changes in gray matter density (Tang et al., 2020; Lazar et al., 2014). It’s now been considered that meditation, along with diet, exercise, socialisation, and mental stimulation, are important components of an Alzhiemer’s prevention programme (Khalsa, 2015). 

Robust evidence has shown that practicing meditation has lasting positive effects on depression and anxiety (Saeed et al., 2019). The ability to observe thoughts rather than engage with them and in doing so break the cycle of rumination, is, in my view, the crux of meditation’s impact on the hyperactive DMN. I’ve definitely felt the benefits. Meditation can be hard, and I feel my hyperactive mind is particularly averse to it. But that just makes me more conscious of how much I should be meditating. The times I’ve done it regularly enough are times I’ve felt a clearness of mind that I rarely feel in my day-to-day. For those that struggle with an overactive mind or excessive rumination, which I feel is not uncommon in this hyper-stimulated social media generation, meditation will surely do some good.