Dreams largely occur during REM sleep (but not entirely)

Researchers believe the brain consolidates memories, processes emotions, and plans for the future during dream states

The evolution of dream science—from interpretation to advanced brain imaging

In the mid-1900s, dream scientists would tape study participants' eyes open, wait for them to fall asleep, and attempt to influence their dreams by shaking, tickling, and more. Now, advanced techniques like MRIs have shed new light on what’s happening in the brain as we sleep.

How new research sheds light on why we dream

The theory of where dreams originate began shifting from ancient mystical explanations to modern scientific ones at the beginning of the 20th century. Now, scientists have the ability to track electrical activity in the brain, solidifying some of the field's softer science into observable data and giving rise to sleep labs.

While dreaming, the brain connects new information with already-stored memories

During dream sleep, the brain makes connections between new information learned during the day and information already stored in the mind, creating a revised mind-wide web of associations. The dreamer also temporarily becomes confused about time and place and is subjected to a pendulum of strong emotions.

We dream for around two hours each night, on average

Every night we lie down to rest, we spend about two hours traveling through seemingly real experiences as dreams bubble up from our subconscious during various phases of sleep. Despite the ubiquity of the experience, where dreams come from—and what their purpose is—remains largely unanswered.

The dreaming brain, as understood by scientists

Technology has advanced to where the seemingly separate fields of psychology and neuroscience are asking the same questions about dreams, such as whether they're more closely related to perception or visualization. Some field-intersecting findings include research that shows people with impaired face perception don't dream of faces, those with brain legion-related cognition difficulties deal with similar issues in dreams, and children's dreams change in parallel to their cognitive development.

Delta brain waves happen during deep sleep, while REM cycles resemble being awake

As the brain cycles from wakeful rest to deep sleep, different brain waves emerge. Alpha waves occur during restful waking states, while theta waves can be associated with light sleep and meditation. Delta waves are observed during deep sleep—but REM cycles more closely resemble active awake states.

Why don’t you remember all your dreams?

Despite being a near-nightly occurrence, we remember very few of our dreams. Researchers believe reduced activity in regions where memories are stored, a different neurochemical environment during sleep, and rapid transition during waking contribute to this phenomenon.

How dreams affect your memory

In 1999, scientists conducted a study in which participants were asked to recall images flashed before them for milliseconds. They found that participants who slept before recalling the information performed better than those who had been asked to recall the same information that same day. This was some of the earliest convincing evidence of how crucial sleep is for learning and memory, findings that current research continues to strengthen.

The REM cycle happens around four to six times per night

Sleep is a natural process that is critical to maintaining life—a process conserved throughout evolution across just about any animal with a brain. Generally speaking, the first three stages involve increasingly deep phases of non-REM sleep, followed by a roughly 90-minute period of REM sleep that repeats throughout the night.

The brain consolidates memories during sleep

During sleep, the brain appears to process memories from the day and encode them into long-term storage. At the same time, the brain prunes old memories out of the brain that are no longer useful. Understanding this process also sheds light a various neurodegenerative diseases.

Brain studies suggest some animals do dream (sort of)

Studies on sleeping cats, rats, fish, and finches show that their brains fire as if performing actions from waking life. Spiders and insects also have REM-like sleep. Whether these findings indicate that animals dream depends on one's definition of dreaming.

The neuroscience of REM atonia disorders, where patients act out dreams

What prevents the typical person from acting out their dreams? Temporary paralysis of skeletal muscles, usually leading up to, and during, REM sleep. This academic article and related graphics explore what happens when this process doesn't go as planned, leading to REM sleep behavior disorder.

The hippocampus plays a central role in dreaming

It's theorized that the hippocampus—a brain structure involved with memory formation and the simulation of imagined and novel scenarios using those memories—plays a major role in dreaming. Studies of people with damaged hippocampi show that they still dream, but their dreams lack the richness of detail described by others.

Why do dreamers twitch?

This thought-provoking piece highlights newer research suggesting sleep twitches may not be random dream leftovers, but instead a crucial way our brains map and understand our bodies. From sleeping rat pups to dreaming octopi, this biological mapping system appears universal across animal species.

How your subconscious influences your decisions

How much of your desires and daily choices are truly yours? One of the most effective ways to influence someone's subconscious is when they're asleep. To study this possibility, researchers trained participants to be able to dream lucidly, a phenomenon that occurs when a dreamer knows they're dreaming.

Several brain regions are involved in lucid dreaming

Some scientists propose that lucid dreaming may require the emergence of a brain network, which is when multiple brain regions collaborate to perform certain functions. Research shows that lucid dreaming is associated with increased activity in the frontal lobes—associated with decision-making, voluntary movement, attention management, and more.

Modern media exposure may impact whether people dream in color or black and white

A 1942 study found that 70.7% of college sophomores rarely saw colors in their dreams, while a similar survey in 2003 showed that only 20% reported the same. The prevalence of color television and films may make color dreams or the recollection of color features easier to remember.

What do your dreams mean, according to science

Humans have been interpreting dreams as signs from deities, spirits, or the psyche for ages, and research shows that reflecting on and analyzing one's dreams can be beneficial. In alignment with dreams' elusive nature, they have no objective or clearly assigned meaning. However, variations of common dreams, such as a surprise exam in a forgotten class, are rife with shared primal fears.

Dreams have long been used for religious and political power

Classic literature and mythology attests to the crucial role dreams play in narratives, from the Virgin Birth to the prophetic visions of Gilgamesh and Enkidu. The heightened state of dreaming and its analog, hallucinating, have long held special power over the collective imagination.

Cerebrospinal fluid flushes waste from your brain during sleep

Recent research suggests a nightly brain cleanup as an important purpose of sleep. Brain waves have been observed to work in lockstep with the brain’s blood flow and cerebrospinal fluid flow, allowing for a cleansing tide that washes away toxic waste.

Sleep is often viewed individually, when its impact and meaning may be more communal

At any given point, roughly 2 billion people may be asleep on Earth. The typical scientific description of sleep focuses on its individual impact, but the phenomenon shapes whole cultures and eons. This essay prompts a fresh rethinking of the importance of sleep for humanity.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

Nightmares are unpredictable, but are linked to stress, anxiety, trauma, and more

Nightmare comes from the terms "night" and "mare," an Old English word for evil, suffocating spirits. Nightmares are parasomnias, meaning they are undesirable events experienced during sleep, and may stem from building tensions in one's unconscious.

Only a fraction of LSD reaches the brain, but it concentrates in key regions

When taken, LSD is absorbed quickly (often within an hour of ingestion) and exerts its effects primarily by binding to serotonin receptors. While only a small amount enters the brain, it's active in regions controlling the visual and auditory senses, potentially driving its psychedelic effects. The drug doesn't linger in the body, and is typically undetectable within a day.

Four in 10 CPR patients report consciousness not captured by standard measures

A recent study found people revived by CPR after cardiac arrest reported they experienced some amount of consciousness during clinical death, suggesting our brains are capable of thought and memory for significantly longer after death than previously thought.

The human brain only uses 5% more energy during active tasks versus resting

Despite only being 2% of the weight of a human body, the average adult brain consumes 20% of its energy, with the majority of it spent on maintaining homeostasis—the stable equilibrium conditions of temperature, acidity, blood sugar, and other properties in the body. For infants, the consumption is closer to 50%.

After 25 people used virtual reality headsets to practice flying with virtual wings—flapping their arms—their visual cortex responded to the wings almost as if they were real arms, treating them as body parts.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

The Dracula character, now seen as the vampire archetype, was inspired by a seafood-induced nightmare its creator experienced.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

Explore the known asteroids, comets, and spacecraft involved in asteroid studies within our solar system with 'Eyes on Asteroids,' a 3D visualization from NASA.

In 1945, Surrealist artist Salvador Dalí and legendary animator Walt Disney began collaborating on a short film that was not completed until 2003, years after both men had died.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Doctors differentiate between a phobia and fear by asking patients whether their fear interferes with their day-to-day activities.

Explore an interactive map built from more than 100,000 survey responses on where people find joy in their lives

Browse a detailed visual analysis of over 200,000 similes—comparisons that often use 'like' or 'as'—from popular fiction to see how frequently writers the same idiomatic expressions.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

Explore the archaeological treasures of Pompeii, the city buried under volcanic ash when Mount Vesuvius erupted in 79 CE.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Netflix profits when you're not watching, and its movies are designed that way—read a detail-rich critical essay exposing lesser-known Netflix takes

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.

The 19th-century painters of the Hudson River School were among the first American romantics, with portraits that displayed the natural beauty of the young country.

Long before Major League Baseball began allowing instant replay for balls and strikes, an umpire reluctantly used the technology to determine whether a hit was a home run, a move that inadvertently ushered in a new era for the sport.

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