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

The REM cycle—named for the 'Rapid Eye Movement' that occurs during this stage of intense dreaming—happens around four to six times per night.

Your brain moves through four distinct sleep stages every night

Each stage plays a key role in memory, repair, restoration, and other key biological functions. The full cycle generally proceeds from light sleep and deep rest into vivid REM dreaming, which repeats between three and five times nightly.

Dreams largely occur during REM sleep (but not entirely).

Sleep is no longer considered a binary state—scientists are seeking to map a variety of liminal states between sleep and waking, including the hypnagogic state associated with boosts of creativity.

Dream interpretation has evolved from ancient mystical explanations, to dream reports, to tracking electrical activity in the brain and more.

Sharp wave ripples in the brain tag experiences for long-term memory storage

These ripples were known to quickly replay neuronal sequences during sleep for consolidation. While awake, they help the brain prioritize memories to remember, and their disruption can impair memory formation.

Animal brain studies show brain activity similar to what we'd expect during dreams, but parsing whether animals are truly dreaming depends on how one defines dreaming and how scientists could prove it.

Brain activity sometimes goes into overdrive around the point of death according to researchers' recent analysis of patients' brains before and after they were taken off their ventilators.

Cerebrospinal fluid flushes waste from your brain during sleep, performing a nightly brain cleanup that's an important purpose of sleep.

Studies of psychedelic use may help shed light on the nature of consciousness

The nature of consciousness—what it is, where it comes from, and how it manifests as moment-to-moment experience—remains under debate by scientists. Recent studies show psychedelics were found to boost low-frequency brain signals known as delta waves, a behavior also seen during dream states.

Sleepwalking, or somnambulism, is a bit of a misnomer since many things can occur during this state, including speaking, using the bathroom, and more.

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.

We dream for around two hours each night, on average, but the exact purposes of dreams remains under investigation.

During dream sleep, the brain connects new information learned during the day with information already stored in the mind, creating a revised mind-wide web of associations.

People with a sleep disorder called REM Sleep without Atonia don't experience the temporary paralysis of skeletal muscles that typically occurs during REM sleep—instead, they have vivid dreams that they act out during sleep.

Forty to 110 minutes of deep sleep is recommended per night

Adults typically spend 10% to 20% of the night in deep sleep, also known as slow-wave sleep, with the rest of the night spent either in light sleep or REM states.

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.

Sleep research published in 2021 confirmed that there is a 'creative sweet spot' when people are drifting off to sleep, and that if they wake up at that point to work, it can boost their creative problem-solving.

Sleeping on a problem does seem to help—in fact research published in 2026 suggests scientists can seed people's dreams with sound cues about a difficult puzzle during REM sleep and they'll be better able to solve it.

Understanding the stages of sleep

Do you have trouble keeping the different stages of sleep straight and organized in your mind? Us too. Sometimes it helps to have a straightforward listing of what each stage is and why it’s important. Look no further than this resource from Lumen. It is a basic outline of the four stages of the sleep cycle, along with the brainwaves and attributes that characterize each. If you’re brave enough, test yourself on the built-in quiz!

What happens when we sleep

Sleep is a highly specialized and complex process that begins via signals from a region of the brain called the hypothalamus. As explained in this overview video from The Economist, the hypothalamus maintains our circadian rhythm by using light cues from our environment to regulate sleep via a compound known as melatonin. Once asleep, the brain begins the "sleep cycle" and progresses through the four stages of sleep over and over again each night.

Neural rhythms shape how we move, focus, remember, and interact with the world

Millions of neurons in the brain produce rhythmic electrical signals, or brain waves, that guide physical movement and help form and store memories. Researchers also use these rhythms to create brain-computer interfaces, letting people control devices using only their thoughts.

Several brain regions are involved in lucid dreaming, a state in which a person knows they're dreaming.

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.

A deeper walk through of the four stages of sleep

In this TED video, sleep expert Matthew Walker carefully breaks down the sleep stages along with a description of why each is important. He finishes the discussion by examining the consequences of altered or decreased sleep, and why seemingly small alterations in our sleep patterns can have outsized effects.

The study of dreams, formally called oneirology, has evolved over the centuries, from anecdotal interpretations to advanced brain imaging.

The body's sleep-wake cycle is one of its many circadian rhythms

The body's sleep-wake cycle is one of its many circadian rhythms, which are behaviors or biological processes that exhibit 24-hour patterns. These rhythms are deeply impacted by light exposure, food availability, and much more, meaning where you live impacts your sleep.

The brain will attempt to rest itself in periods of chronic sleep deprivation

Skimping on sleep lengthens reaction times and blunts decision-making skills. At a certain point, the brain will try to sneak sleep where it can, shifting sections offline even as you remain awake. Going without sleep raises blood pressure, undermines the immune system, and increases one's risk of dementia.

The hippocampus, located deep inside the temporal lobe, appears to play a central role in dreaming and memory, according to recent research on dreaming and damage to that area of the brain.

What happens in a dying brain?

Near-death experiences usually happen during death or on the border of life and death when a person isn't understood to be conscious. This article details the science of what's going on with the brain during NDEs.

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.

Wearable sleep trackers like the Oura have variable accuracy for specific sleep-stage data but are helpful for identifying overall trends.

Sleep research indicates dogs likely dream about their toys, food, and owners.

Five patterns may define how we sleep—not just night owl or early bird.

This is the human brain on the world's strongest psychedelic

Within seconds of inhaling a high dose of vaporized synthetic 5-MeO-DMT—a lab-produced substance that otherwise is naturally derived from the glands of the Colorado River toad—it induced slow brain waves. Such waves are typically associated with unconsciousness due to a coma or anesthesia, perhaps explaining why users describe feeling like everything falls away. The compound is currently in clinical trials for treating depression.

Scientists are studying dying patients' brain activity in the final moments of life

In the final moments of life there are distinctive bursts of coordinated neural activity. Researchers are interested in parsing that data to better understand the dying process and also exploring how this data relates to our understanding of consciousness.

Sleep paralysis occurs when the body fails to 'unfreeze' in sync with waking.

What is the brain up to when the mind wanders?

As you stare into the distance while washing your home's seemingly never-ending pile of dishes, the brain activates its default mode network. This collection of "task-negative" brain regions associated with memory, reward, action consideration, and prediction alight with activity when humans mentally turn inward, possibly giving rise to the brain's ability to wander and humans' ability to construct internal narratives about the world.

The body's response to cardiac arrest has been linked to near-death experiences.

An estimated 1 in 250 people—a small subset of the population—reports they've never remembered a single dream.

How four types of psychedelics affect the brain

Brain imaging shows that ayahuasca, MDMA, DMT, and psilocybin profoundly affect neural activity, giving rise to higher states of introspection and consciousness. This article details exactly how each of these drugs physically affects the brain and what that means for mental health treatment. Some of these drugs quiet the brain or trigger the release of neurochemicals associated with mood regulation and learning.

Emerging research suggests that cannabis, used by about 9% of American adults as a sleep aid, may suppress rapid eye movement and lead to worse quality sleep and fewer remembered dreams.

Explore a series of bedtime exercises to improve sleep

Low-impact, mindful movements can potentially help the body and mind relax before sleeping. Such exercises could be a helpful complement to regular exercise during the day.

Scientists are learning to guide your dreams using sound and touch.

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.

Poor sleep increases the risk of developing Alzheimer's, and a main reason appears to be that the brain disposes of toxic protein buildup during high-quality sleep.

Similarities between human and animal sleep

Have you ever noticed the wide-ranging differences in sleep between humans and animals? Sleep as a necessity is present amongst all animal species, but the specific patterns of sleep vary widely. Just think of the differences between how an owl, a whale, and a horse might sleep. This helpful resource from the Sleep Foundation explores the relations between human and animal sleep, complete with some fascinating statistics about sleep patterns throughout the animal kingdom!

Anesthetics slow brain activity by promoting inhibitory neurotransmitters

Drugs like propofol and isoflurane increase activity at the GABA receptor, which opens chloride channels. These ions enter neurons and hyperpolarize them, making them less likely to fire. Dexmedetomidine instead blocks norepinephrine receptors in the brainstem to sedate patients.

Deep brain stimulation helps manage movement in patients with neurological disorders

DBS is a surgical procedure that uses implanted electrodes to send electrical signals to targeted areas in the brain, interrupting abnormal neural activity. It may be implemented when medications lose effectiveness or cause disruptive side effects.

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.