The science of dreams: what happens in the brain when we dream

TL;DR:

What happens when we dream may still feel mysterious, but research is beginning to uncover what’s happening in the brain. During REM sleep, brain activity increases—especially in the regions that regulate memory and emotion. While the science behind dreams is still unfolding, experts believe dreaming helps us process emotions, store key memories, and prepare for challenges we face when awake.

Let’s be real - dreams are dreamy. There’s so much we don’t know about them, and yet they can reveal so much. From flying through clouds to seeing people from your past, our dreams are full of mystery and meaning.

For centuries, humans believed dreams were messages from the gods or windows into the subconscious(1).Today, science is beginning to unpack what really happens in the brain while we sleep—and why dreams might serve a deeper purpose than we once thought.

In this article, we’ll explore the science behind dreaming: how dreams are formed in the brain, what REM sleep really does, and why you often can’t remember a single thing by morning.

How do dreams work?

Dreaming has fascinated humans for centuries. When you look at ancient civilizations, they believed dreams were prophecies or divine messages (2), and Freud later proposed they revealed repressed desires (2). While the exact purpose of dreaming remains unclear, modern science has shifted the conversation from symbolism to brain function, offering new insights into what happens when we sleep(3). 

REM sleep 

REM sleep, known as the stage where dreams are most vivid—activates areas like the amygdala, hippocampus, and visual cortex, while deactivating the prefrontal cortex, which explains why dreams often feel illogical (3). These neural patterns support theories that dreams help process emotions, consolidate memory, and simulate real-life scenarios. REM sleep also supports neuroplasticity, as it can strengthen and organize neural connections tied to learning and memory.

To activate REM sleep, one needs to get sufficient sleep, which is 7-9 hours per night,(4), and studies show that REM periods lengthen and intensify in the final sleep cycles (5). REM sleep has been linked to emotional regulation, creative insight, and next-day problem-solving (6;3). 

Alternative function of dreaming

Some researchers believe dreams serve practical functions beyond storytelling. The threat simulation theory suggests dreaming evolved to help us mentally rehearse danger in a safe, low-risk setting (15). 

Others argue dreams act as neural housekeeping, clearing out irrelevant memories to make space for more useful ones (16). While no single theory has been proven, most agree that dreaming reflects coordinated brain activity tied to memory, emotion, and adaptation.

Read more about harnessing your subconscious mind through sleep >

What part of the brain controls dreams?

Dreams aren’t driven by a single control center—they emerge from a network of brain regions working together. Research shows that the default mode network (DMN), a system linked to spontaneous thought and imagination, remains active during REM sleep and may help construct the narrative flow of dreams (9). 

The parietal lobes, which help the brain understand space and where things are, are thought to support the immersive, scene-like quality of dreams—like walking through a room or flying over a city (10). The temporo-parietal junction (TPJ), where the temporal and parietal lobes meet, has been linked to self-awareness during dreaming, and may play a key role in lucid dreaming, which is when someone realizes they’re dreaming while it’s happening (11).

Despite advances in neuroscience, there’s still no single, proven theory that explains exactly why we dream or how dreams are generated in one definite way. Crazy, right?

Dreams & what’s happening in the brain

Dreaming is such a fascinating topic because everyone dreams (even if you don’t remember them), but the experience of dreaming can vary from person to person. We do know that most dreams last about 5-20 minutes, and you can have multiple dreams in a night. The variability is in the experience of dreaming, recollection, and intensity (12).

Some people remember their dreams vividly, and others do not. Some have the same dream over and over while others rarely repeat a dream. Some remember only a handful of dreams in their lifetime but others can recall dreams nightly. Some are lucid dreamers, and most of us are not. Others dream in color, while some dream in black and white (13).

 

Muse’s EEG Spectogram image above shows the intensity of brainwave activity over time. High-intensity regions are indicated by tones of red, yellow, green, and low-intensity regions are indicated by tones of blue.

Up until the advent of the electroencephalogram (EEG), researchers were unable to access or measure electrical activity that occurs in the brain during all states of consciousness. It was once assumed that the brain simply “shut off” at night—but we now know that’s far from true. In fact there are varying levels of brain activity that occur during different stages of sleep. As we cycle through different sleep stages, the brain shifts between distinct brainwave frequencies like alpha, theta, delta, and beta—each linked to different levels of awareness, rest, and recovery.

A deeper look: dreams in REM

You can dream in any stage, but most dreaming appears to occur during the REM stage. During REM sleep, brain activity most closely resembles that of a wakeful state (14). People also tend to remember most of their dreams in a REM state, compared to other states, and after REM sleep, i.e. a restful, nourishing night of sleep, cognitive function improves. This is something you can measure with the Muse headband. 

Interestingly, a study conducted by J. Allan Hobson at the Division of Sleep Medicine at Harvard Medical School proposed that “REM sleep dreaming can be viewed as a virtual reality created from our brain’s devise.” In other words, “we sense, we act and we feel” what we dream (15). The theory inspired a team of sleep engineers at MIT’s Sleep & Neurophysiology Lab to investigate if receiving sensory stimuli while sleeping could shape our dreams.

Muse’s sleep stages graph (hypnogram) above shows the different stages of sleep of participants during their session.

 

To do this, they recorded a group of participant’s body and brainwave patterns while sleeping and computed their sleep stages and sleep scores using Muse. While asleep, participants underwent sensory dream engineering techniques using Dormio, the first interactive interface for sleep. These techniques include; receiving a burst of scent or placing a heated eye mask over their eyes (16). So, what did the study uncover?

1. Ameliorated Dream Valence – After introducing pleasurable or familiar scents and temperatures, participants showed positive affective responses (17) while dreaming that are associated with patterns of respiration, heart rate, and muscular activity (particularly during REM sleep), improved sleep quality, and mood.

2. Alleviated Nightmares – Participants showed fewer biomarkers associated with nightmares, such as increased and elevated heart rate, increased eye movements, increased respiration rate, and the interference of REM sleep.

When you dream, your whole brain is active at some level. However, during REM sleep, your prefrontal cortex is less active. This is the part of the brain that is responsible for planning and logic. Since activity in the prefrontal cortex is lower during REM sleep, we often don’t recognize the strangeness or implausibility of a dream until we wake up (2). This is why your ability to fly or the appearance of monsters seems so realistic until you wake up from that dream (or nightmare).

Modern theories on dreams

While the science behind sleep and sleep tracking continues to evolve, some modern theories suggest that dreams may not carry deep symbolic meaning at all. Instead, they may be the brain’s way of stitching together fragments of recent memories, thoughts, or emotional residue—often from the things we’ve been thinking about most.

Still, other researchers argue that dreaming serves a deeper function—one that plays a vital role in cognitive health and emotional resilience. As we better understand the relationship between sleep and mental fitness, tools like Muse allow us to track brain activity in real time, revealing how quality sleep can impact focus, stress, and recovery.

Here are three leading theories on why we dream:

1. Memory Consolidation

Sleep is essential for memory formation. Without enough rest, the brain struggles to retain and recall information. Some researchers believe that REM sleep—and the dreaming that occurs during it—helps sort, store, or even discard memories. In this view, dreaming is like a nightly cleanup: clearing space for more relevant information to take hold (1).

2. Evolutionary Purpose

Because dreaming is present in other mammals, some believe it serves an evolutionary function. One theory suggests dreams allow us to mentally rehearse difficult or threatening situations, helping us become more adaptive in waking life. Others propose that dreaming supports problem-solving in a safe, altered state—essentially a sandbox for the subconscious (2).

3. Emotional Processing

REM sleep may play a vital role in helping the brain regulate emotions. A  study from the Sleep and Neuroimaging Laboratory at Berkeley found that during REM sleep, the limbic system—which processes fear and emotion—becomes highly active while also working to block negative emotions such as fear and anger (18). This process may help reset emotional sensitivity, which explains why people who get less REM sleep (and therefore dream less) often show more difficulty managing emotions in their waking hours.

So while the exact purpose of dreaming isn’t fully proven, the evidence suggests it may serve multiple roles across memory, survival, and emotional balance—all essential components of mental fitness.

Even though we may not fully understand why we dream, or how the brain pulls it off so vividly, what we do know is this: dreams aren’t just stories we sleep through. They’re a sign that the brain is working, adapting, and healing in the background. And thanks to tools like Muse and digital sleeping pills, we don’t have to leave that mystery entirely in the dark. 

Start tracking today, and start improving your mental fitness by starting with your sleep!

Frequently asked questions about dreams & the brain

What happens in the brain when we dream?

When we dream, especially during REM sleep, brain activity increases in regions like the amygdala (emotion), hippocampus (memory), and visual cortex (imagery), while the prefrontal cortex (logic) quiets down. This combination allows dreams to be vivid, emotional, and often surreal.

What part of the brain controls dreaming?

Dreams are shaped by a network of brain regions, including the default mode network (DMN), parietal lobes (spatial awareness), and the temporo-parietal junction (linked to self-awareness and lucid dreaming). There is no single "dream center."

How long do dreams last?

Most dreams last between 5 to 20 minutes, and you can have several dreams throughout the night, especially during longer REM sleep cycles in the second half of your sleep.

Can you control your dreams?

Yes—this is called lucid dreaming. It happens when the dreamer becomes aware they’re dreaming and may even influence the dream’s direction. Lucid dreaming is often linked to activity in the temporo-parietal junction (TPJ).

Why don’t we remember our dreams?

You’re more likely to remember a dream if you wake up during or right after REM sleep. Low activity in the prefrontal cortex during REM may also limit the brain’s ability to encode dream content into long-term memory.

Does dreaming serve a purpose?

While still debated, current research suggests dreaming may support emotional regulation, memory consolidation, and problem-solving. Some scientists also believe it helps the brain "reset" emotional responses after stressful experiences.

References:

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2. Big Dreams: The Science of Dreaming and the Origins of Religion, https://books.google.ca/books?hl=en&lr=&id=_zh2CwAAQBAJ&oi=fnd&pg=PP1&dq=science+of+dreaming+scholarly+articles&ots=XhMok2QgJ1&sig=_RvNr2wjkwpQyug3LnoN8Z3I3mg#v=snippet&q=gods&f=false 

3. Walker, M. P. (2017). Why we sleep: Unlocking the power of sleep and dreams. Scribner. 

4. Hirshkowitz, M., Whiton, K., Albert, S. M., Alessi, C., Bruni, O., DonCarlos, L., ... & Croft, J. B. (2015). National Sleep Foundation’s sleep time duration recommendations: Methodology and results summary. Sleep Health, 1(1), 40–43. https://doi.org/10.1016/j.sleh.2014.12.010

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6. Gujar N, McDonald S, Nishida M, Walker M. A Role for REM sleep in Recalibrating the Sensitivity of the Human Brain to Specific Emotions. Cerebral Cortex January 2011; 21:115-123. https://walkerlab.berkeley.edu/reprints/Gujar-Walker_CC_2011.pdf

7. Revonsuo, 2000
   Revonsuo, A. (2000). The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming. Behavioral and Brain Sciences, 23(6), 877–901. https://doi.org/10.1017/S0140525X00003976

8. Izawa et al. REM sleep-active MCH neurons are involved in forgetting hippocampus-dependent memories. Science, September 20, 2019 DOI: 10.1126/science.aax9238 https://science.sciencemag.org/content/365/6459/1308.abstract

9. Domhoff, G. W. (2011). Dreams are embodied simulations that dramatize conceptions and concerns: The continuity hypothesis in empirical, theoretical, and historical context. International Journal of Dream Research, 4(2), 50–62. https://doi.org/10.11588/ijodr.2011.2.9137

10. Fox, K. C. R., Nijeboer, S., Solomonova, E., Domhoff, G. W., & Christoff, K. (2013). Dreaming as mind wandering: Evidence from functional neuroimaging and first-person content reports. Frontiers in Human Neuroscience, 7, 412. https://doi.org/10.3389/fnhum.2013.00412

11. Boly, M., Balteau, E., Schnakers, C., Degueldre, C., Moonen, G., Luxen, A., & Laureys, S. (2008). Baseline brain activity fluctuations predict somatosensory perception in humans. Proceedings of the National Academy of Sciences, 104(29), 12187–12192. https://doi.org/10.1073/pnas.0611404104

12. National Institute of Neurological Disorders and Stroke. (2020). Brain basics: Understanding sleep. National Institutes of Health. https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep

13. Harvard University: Natural Patterns of Sleep. http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem

14. Bulkeley, K. (2016). Big dreams: The science of dreaming and the origins of religion. Oxford University Press. https://books.google.ca/books?id=_zh2CwAAQBAJ 

15. Carr, Michelle, Adam Haar, Judith Amores, Pedro Lopes, Guillermo Bernal, Tomás Vega, Oscar Rosello, Abhinandan Jain, and Pattie Maes. “Dream engineering: Simulating worlds through sensory stimulation.” Consciousness and cognition 83 (2020): https://dam-prod.media.mit.edu/x/2020/10/06/1-s2.0-S1053810020300325-main.pdf

16. Horowitz H., A., Grover, I., Reynolds-Cuéllar, P., Breazeal, C., Maes, P., “Dormio: Interfacing with Dreams” Association for Computing Machinery (2018): https://dl.acm.org/doi/10.1145/3170427.3188403

17. Shuman, V., Sander, D., and Scherer, K., R., “Levels of Valence” Frontiers in Psychology 4 (2013): https://www.frontiersin.org/articles/10.3389/fpsyg.2013.00261/full

18.  Bulkeley, K. (2016). Big dreams: The science of dreaming and the origins of religion. Oxford University Press. https://books.google.ca/books?id=_zh2CwAAQBAJ