What exactly is déjà vu?

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.

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.

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

Neuroscientists suggest the phenomenon is your brain recognizing that this feeling of familiarity is incorrect, showing off the brain's internal fact-checking system. Younger people experience déjà vu more often because their brains have higher excitatory activity and stronger memory monitoring systems.

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 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.

What exactly is dopamine?

Dopamine is a neurotransmitter—a chemical released by neurons that enables neural communication—that makes people want things with an "almost animalistic desire," compelling them to snack or check phone notifications. Often misrepresented as a "pleasure" chemical, dopamine is involved in motivation, learning, attention, habit formation, and more. Trends like dopamine fasting overinflate its role in mental health and often use it as part of "straw man" biohacking claims.

University of Virginia has the nation's premier near-death studies department

Researcher Bruce Greyson has been studying this phenomenon at the University of Virginia for decades, where he now directs the Division of Perceptual Studies. This piece from the university’s magazine explores the breadth and substance of the department, founded by pioneer researcher Ian Stevenson.

Why dizziness is still a mystery

Dizzy spells can completely upend the lives of those suddenly struggling to find their footing. Despite this severe impact, the different flavors of dizziness and their sources continue to elude medical understanding. This article follows a health...

The debate on why humans are conscious—and what that means

Understanding what consciousness is, and why and how it evolved, is perhaps the greatest mystery known to science. Watch interviews with the world's leading experts on what it is and whether we'll ever know.

There’s a psychological explanation for ‘FOMO,’ or the fear of missing out

This video breaks down FOMO—what it is, how it works, and why it happens—showing how social comparison and uncertainty trigger anxiety that pushes people toward risk-taking and constant checking behaviors.

Before vaccines, there was 'variolation': what was it?

Before the technology behind vaccinations was discovered, some keen observers of medicine around the globe noticed how previous infections could impact future ones. Learn about the techniques early physicians used before they had vaccines.

Synesthesia: when sensation in one sense triggers an unrelated sense in the brain

The first reported clinical case of synesthesia dates back to the early 1800s, though the perceptual phenomenon may be much older than surviving records imply. This article by researcher Richard Cytowic details the scientific history of synesthesia, a neurological trait that causes some senses to overlap, giving color to numbers and flavors to names.

Scientists are experimenting with ways to probe the multiverse theory

Researchers are simulating vacuum bubbles—the theorized starting points of universes—using quantum computers, digital models, and exotic lab setups to study how they form, expand, and possibly collide. One experiment aims to "blow" artificial universe-like bubbles inside ultra-cold quantum gases, potentially capturing real-time glimpses of cosmic birth processes in a lab.

The earliest mention of time travel

Time travel has fascinated humans for centuries. It appears in myths, literature, and science fiction. One of the earliest examples comes from the 400 BCE Hindu epic Mahabharata, describing time dilation long before Einstein’s Theory of Relativity. By the 19th century, stories introduced machines enabling time travel—setting the stage for modern sci-fi.

A fascinating look at how our DNA is built and replicated

This easy-to-understand 13-minute video dives into the wondrous molecule deoxyribonucleic acid – also known as DNA – and explains how it replicates itself in our cells.

When is someone actually dead?

Death is a process, not a sudden flip of a switch. Technology can now interrupt this process at various stages, begging the question of when exactly death happens in the dying process. This 33-minute podcast episode explores this question and the...

What (and why) is ASMR?

ASMR podcasts and videos are appearing all over social media, so what exactly is it, and what does it do? This immersive article explains the phenomena of ASMR, which stands for autonomous sensory meridian response. ASMR is when certain sounds or...

The history of ghosts, explained

The afterlife has perplexed humans across different periods, cultures, and belief systems. The desire to understand what comes next is often explored through the telling of ghost stories. Learn more about the spooky phenomena here.

Wave-particle duality—a simple overview

Our notion of reality is built on everyday experiences. But wave-particle duality is so strange that we are forced to re-examine our common conceptions. Wave-particle duality refers to the fundamental…

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

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.

De-extinction techniques create new species from existing organisms

Rather than recovering a genetic sample of a lost species and editing it with that of living creature—as has been depicted in science fiction—scientists begin with living cells from close genetic relatives and use tools like CRISPR to swap in extinct versions of specific traits to create new hybrid species.

50 years of research has focused on unraveling the relationship between music and frisson

One insight reveals that musical passages with surprising volume changes or unexpected harmonies and beauty are more likely to trigger frisson, perhaps because they upend listeners' expectations.

Watch a video that visualizes what really happens inside a credit card network when you make a purchase.

Every tap sets off a lightning-fast relay. When someone buys coffee with their Visa, a tiny "runner" races between the coffee shop's bank, Visa's network, and their bank—all in under a second. The catch? No money has actually moved yet. Here's what really happens behind that instant "Approved."

A deep dive on everything you need to know about virtual reality

In the wake of Facebook’s purchase of Oculus VR, can the revolutionary technology triumph anew? These interactive articles chart the rise and fall — and rise again — of VR.

Take a quiz to identify whether you can spot deepfakes

Advances in artificial intelligence have made deepfakes increasingly difficult to identify, as they are intentionally designed to appear real. The technology has exacerbated some of the problems brought on by digital editing tools like Photoshop.

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.

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.

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.

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.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

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

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

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.

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.

Learn more about the history of fireworks, which dates back to an accidental invention during an alchemist's quest for information about immortality.

Ebola is a filovirus, meaning it resembles a thread under a microscope, though it sometimes twists and can resemble a bowl of spaghetti.

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

Venture capital is a form of funding provided to early-stage companies with high growth potential, typically in exchange for an equity (or ownership) stake

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

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

This site reaches millions of visitors who are tired of AI chatbots and seeking human connection. Pretend to be an AI chatbot and ask questions, provide answers, and draw for people in real time.

Apeirophobia is an overwhelming fear of living forever, perhaps stemming from the brain's inability to conceptualize an infinite life.

Listen to an in-depth conversation on the links between Parkinson's disease and herbicide exposure and the challenging pace of scientific investigation.

Explore the animals that populate the depths of the ocean, from fish and coral in the first few hundred feet, all the way down to the bottom of the Mariana Trench.

The idea for the Federal Reserve was conceived in secret in 1910—with bankers donning duck hunt gear for disguise while traveling to a remote country club on Georgia's Jekyll Island

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.

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.

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

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.