DW Science explainer on the default mode network: what your brain does when you aren't focusing on anything, and why it's important.

You know when you lock your phone and the screen goes black? It seems like it's not doing anything. But it's not doing nothing. It's syncing your messages, updating apps, and running other background processes.

Imagine you're sitting on a bus, staring out of a window, taking a shower or walking, and you get that feeling of doing nothing and letting your mind drift?

Well, your mind, the brain, is doing a lot when it feels like you're doing nothing.

It's going over your memories, shaping your sense of who you are, imagining possible futures, helping you understand other people, and connecting ideas.

That's your brain's default mode network (DMN).

Scientists conducted brain-imaging experiments in the 1990s and early 2000s to find out which regions of the brain were active during demanding tasks, like solving a math problem or memory exercise.

But to measure that, they needed a so-called baseline. They needed to know the level of brain activity at rest and during demanding tasks.

So, between the tasks, they asked participants to relax, close their eyes, stare at a fixed point on a wall, or try not to think of anything at all.

And they measured the participants' brain activity both when they were solving a task and doing nothing. That's how scientists noticed the brain was active in up- and downtime.

They noticed that when participants started to focus on a new task, after having done nothing, some brain areas lit up and other areas dimmed down. That suggests those areas that dimmed down must have been active while the participant was apparently — physically and mentally — at rest.

This realization eventually led to the discovery of the default mode network or DMN.

The DMN is crucial because it helps your brain make sense of your life and experiences.

It helps you connect and revisit memories, reflect on who you are, imagine what might happen in future scenarios, understand other people, build meaning from experience, and connect ideas in new ways.

It turns all your memories, experiences, knowledge, emotions and social information into your internal story. Think of that story as a constantly evolving, updated model of who you are and how you engage with the world around you.

But it's important to understand the DMN involves more than one area of the brain. It is a group of brain regions that light up when you're not focused on an external task.

There's another player in your brain that acts as a monitoring system. You can think of it as constantly asking "Is there anything that needs my attention?"

Imagine you're daydreaming while driving, and a car suddenly swerves into your lane.

In a fraction of a second, your daydream disappears and your attention snaps back to the road. That player is called the salience network (SN).

The salience network helps you notice important signals, like a sound, a mistake, pain, an emotion, a threat, or something happening in your body, and helps shift the brain toward attention and control systems when action is needed.

The DMN, SN and attention/control systems constantly interact.

And the DMN doesn't just turn off completely with every hard task. Parts of it can also contribute when tasks involve memory, stories, meaning, or other people.

Smartphones have filled many of the small empty moments of our days — waiting for the bus, standing in line, eating alone, lying on the couch. We are constantly looking at our devices.

So, it seems reasonable to ask: are we crowding out those moments of boredom where DMN kicks in?

Maybe, but, so far, there's no strong evidence that scrolling directly affects mental health by reducing DMN time.

What we do know is that problematic smartphone use can increase stress, anxiety, task-switching, and disrupt sleep.

And sleep loss and stress also have clearer evidence for altering DMN-related brain connectivity.

When your mind wanders, it might produce a great new idea.

But it might also replay an embarrassing thing you did five years ago. Again. And again.

In depression, the self-reflection part of the DMN can get caught in repetitive negative loops that are hard to stop — what's known as rumination.

Scientists have also found that Alzheimer's disease targets key DMN areas, particularly those responsible for your autobiographical memory and remembering other aspects of the past. Which may help explain why memory problems are so central to the disease.

Protect your sleep and take stress seriously. Sleep loss and stress have direct evidence for disrupting DMN-related connectivity.

Take real quiet breaks after mentally demanding tasks, like studying. It can even help you memorize facts for your exam.

Embrace boredom and enjoy doing nothing.

Try to reframe boredom as this essential, energy-intensive active work in your brain that builds your internal narrative and sense of self, consolidates memories, creates connections and sparks creativity.

Try waiting in line without checking your phone. Look out the window next time you take the bus or take a walk without listening to anything.

You can also try scheduling DMN time. It may be the closest thing to a real brain hack.