Déjà vu is a memory illusion involving brain regions correcting inaccurate memories

What is déjà vu?

Déjà vu describes the strange experience of a situation feeling much more familiar than it should. Here's an explanation of theories about why it happens.

Why do you feel like you've been here before?

Walking into a new environment and feeling like you've been there before is a hallmark of déjà vu, a French term meaning "already seen" that describes the sensation of remembering the unfamiliar and may come with "an illusory sense of prediction." Research suggests déjà vu may manifest when there's a hiccup in the brain's familiarity detection and memory recall, forcing one's attention inward to seek the supposed source of familiarity.

How science explains déjà vu

Take a fun look at the science explaining the odd experience of déjà vu, which some theories suggest is actually a sign of a healthy brain.

What exactly is déjà vu?

While people have wondered about déjà vu for a long time, only recently have scientists started experimentally investigating what might trigger it. Read this deep dive into the latest science.

The doorway effect is when people forget their task when entering a new space

The "why did I come in here?" feeling after walking into a room comes from the brain creating event boundaries to organize memories. Mentally revisiting a previous room can help recall tasks and reverse memory loss. (Some readers may experience a paywall.)

Researchers use the brain's ability to edit memories to explore memory deletion

Scientists have successfully implanted false memories in mice after studying how the editing process works in the brain. Beyond potentially deleting memories in those with PTSD, upcoming research may allow clinicians to forecast the onset of neurodegenerative diseases.

Photographic memory isn’t real, but other rare memory types do exist

While 2% of children can recall sensory experiences with extreme detail (eidetic memory) and some adults can remember life events or dates with high accuracy (hyperthymesia), there is no scientific evidence for the flawless recall popularized in fiction. Most memory feats instead rely on training and memorization techniques.

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.

False memories can form during recall when new information is incorporated

Often formed due to suggestion and misinformation, false memories can lead to serious consequences, such as wrongful convictions. The time between an event and recalling it affects one's susceptibility to false memories.

The "reminiscence bump" causes memories from adolescence to last

Research shows that the "reminiscence bump" phenomenon, which applies to memories formed between the ages of 10 and 30, contributes to songs from those ages triggering the most intense nostalgia. This may be due to biological and hormonal changes enhancing memory effectiveness during adolescence.

Memory exists as multiple types stored across various brain systems

Memory isn't one uniform function—it's made up of multiple systems, like declarative (facts/events) and non-declarative (skills/habits), which involve different brain areas such as the hippocampus, amygdala, and cerebellum.

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.

Super recognizers may use specific facial features to commit faces to memory

Researchers believe that recognizing individuals seen only in passing, even decades later, is an ability of genetic origin and specific to facial recognition, rather than a result of better overall memory or perception. Applying eye tracking data from super recognizers to AI has led to improvements in facial recognition software.

Individuals with synesthesia experience involuntarily overlapping sensations

Tasting words or seeing colors in music results from the brain retaining extrasensory connections from infancy. While most lose these neural pathways during development, about 4% of people are synesthetes, maintaining them without realizing it's unusual.

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

Smell is a robust memory cue for individuals with Alzheimer's disease

Odor is more effective than both visual and verbal cues for triggering autobiographical recall in Alzheimer's disease, according to 2021 research.

Visualizing 11 cognitive biases that influence how you think

Humans are hardwired to make mental mistakes called cognitive biases, affecting the way we view our world. Among the most common are confirmation bias (seeking only evidence that affirms your views), authority bias (overweighting things said by authority figures), groupthink (assimilating ideas to avoid conflict), and more. This quick chart gives an overview of some of the most notable ways we mislead ourselves.

NDEs typically change people's outlooks drastically and can prompt depression

The phenomena are regularly categorized as hallucinations, but some specialists are interested in their psychological nuances. Many survivors report feeling less anxiety about death, though some surveys show the experiences can increase physiological sensitivities.

When to see a doctor over memory lapses

Memory includes various, distinct functions, like working memory (storing information temporarily) and procedural memory (your body's ability to perform a task unconsciously). Forgetting a word or losing your keys can feel like red flag memory lapses, but they are, in fact, language or attention problems, not memory ones. However, a lapse on top of stress, lack of sleep, chronic dysfunction, or an injury may be a red flag to see your doctor.

Vertigo is a mismatch of information between the eyes and the ears

Both vertigo and motion sickness can be caused by mismatches between visual and auditory inputs.The brain relies on inputs from the eyes, inner ear, and receptors in muscles and joints to orient the body. When the eyes suggest movement but other signals suggest the body is stationary dizziness and nausea can occur.

Why do we sometimes jolt awake before falling asleep?

Around 70% of people are estimated to experience the sensation of falling and jerking awake right as they're about to drift to sleep. That mysterious phenomenon is called hypnic jerking. As common as it is, hypnotic jerking remains disconcerting and hard to explain. While we don't yet have clear answers, peruse this article in Popular Science for some possible explanations as to why this happens.

AI hallucinations are inaccuracies or falsehoods in generated content

AI hallucinations are a by-product of the sequential creation of content based on patterns in text, which may not reflect the context or meaning behind a prompt. Back-end issues like biased datasets and overfitting of model data contribute to hallucinations.

Why patterns in art are so pleasing

Repeated visual cues like shapes or lines derive from the brain's innate compulsion to identify faces, places, bodies, and more. With repeated shapes, the brain seeks out resolution to the subtle variations between them. See examples in art and music.

How neurons give rise to thoughts

Neurons in the brain are singular nerve cells that flicker on and off or connect to each other based on incoming stimuli. The more neurons communicate by firing electrical impulses through tendrils known as synapses, the stronger their connection becomes. The electrical energy zipping along these interneural connections in an attempt to classify and respond to incoming stimuli may be what gives rise to thoughts.

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

Prolonged stress impairs the prefrontal cortex

Burnout isn't just a feeling—it physically affects the brain. Prolonged stress impairs regions of the brain responsible for decision-making, emotional control, memory, and more. It can also lead to chemical imbalances, like reduced dopamine and norepinephrine levels, that worsen these effects.

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.

People learned to fly in VR, and their brains then accepted wings as body parts

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. The brain research has potential implications for how VR training may help people adapt to prostheses. (Free with email.)

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.

Salvador Dalí believed he was his own dead brother, who had died nine months before he was born

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.

The concept of phantom limbs, the perception that amputated limbs are still present, dates back to a French military surgeon in the 16th century.

Fear or disgust related to clusters of holes and cracks, called trypophobia, may stem from evolutionary processes to help us avoid pathogens.

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.

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.

Elk Cloner, the first computer virus to spread in public, was written as a practical joke by Richard Skrenta, a Pittsburgh high school student.

Stars appear to twinkle because turbulence in the motion of molecules in Earth's atmosphere causes light to bend and wiggle rapidly on its way to the surface—a phenomenon called scintillation.

When a Paris department store hesitated to sell Estée Lauder's perfume, she 'accidentally' broke a bottle, causing the smell to spread throughout the store and shoppers to start asking to buy the scent.

A researcher recently discovered an interview from 1967 between groundbreaking journalist Joan Didion and the Grateful Dead, years before the band became an institution.

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

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.

Dorothy's famous entrance into Oz in 'The Wizard of Oz' relied on analog tricks, including a body double and sepia-toned paint, as much as it did on technology

The original copy of the Declaration of Independence is not a pristine document, and even features a smudged anonymous handprint in the bottom left corner.

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

For centuries, Niagara Falls has been a magnet for daredevils seeking to conquer one of nature's most powerful wonders, with its 200-foot drop and water rushing at 32 feet per second with 280 tons of force.

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

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

At the beginning of the 20th century, a group of young men ate standard American food—replete with food additives like borax and formaldehyde—as part of government research to better understand food safety.

An Ebola vaccine was developed during the 2018 west African Ebola outbreak, but the 2026 Ebola outbreak is with a different species of the virus, not the one that the vaccine is approved to treat.