What Is Déjà Vu?

Medically Reviewed by Zilpah Sheikh, MD on February 14, 2024
Written by Shawna Seed, WebMD Editorial Contributor
5 min read

Have you ever had the sense that you’ve done something or gone through a new situation before? Does it seem like you know what’s going to happen next? That feeling is often described as déjà vu, which is a French expression, meaning "already seen."

Some people think that déjà vu is a sign of a potential psychic phenomenon. But there may be other causes for your déjà vu experiences.

Around 60%-70% of people in good health feel some form of déjà vu during their lifetime. A familiar sight or sound can trigger the feeling. You may walk into a room in a building you’ve never visited and yet feel like you know it intimately. Most feelings of déjà vu disappear quickly, which can make it hard for you to recall specific details about the experience.

Déjà vu happens most often to people ages 15-25 years. We tend to experience the feeling less as we age. If you travel a lot or regularly remember your dreams, you may be more likely to experience déjà vu than others. Someone who is tired or stressed may be prone to déjà vu feelings, too. Most people have the experience during the evenings or on the weekends.

What explains the déjà vu experience? Researchers have several theories.

Dual processing

This theory suggests that your brain goes slightly off-track while processing information, leading to a sense of déjà vu. The idea is that some cognitive processes in your brain that normally work perfectly in sync become uncoupled. Scientists have a few different theories about how dual processing might play out:

  • Familiarity and retrieving: The parts of your brain that recognize familiar things and recall why they're familiar are supposed to work together. If you recognize something as familiar without the recall process kicking in to tell you where you recall it from, that may feel like déjà vu.
  • Encoding and retrieving: Think of encoding as input -- your brain is taking in information and processing it as memories. Retrieval is the opposite -- playing information that's already been encoded. These two processes work separately. But if they switch on together, you might think that the new information you're taking in is actually old information you're retrieving.
  • Dual consciousness: Some experts suggest that our brains have two types of consciousness, one focused on the world outside us and one focused on our inner mental processes. The dual consciousness theory of déjà vu suggests that when you're tired or distracted, you might mistake what you perceive with your outer-focused consciousness as a product of your inner-focused one. So something new you see may seem to be a memory.

Memory

Memory gets stored in the temporal lobe of the brain. This part of the brain helps us recognize familiar experiences. Although science has yet to prove that everyday déjà vu experiences are a result of memories stored in the temporal area, some researchers believe there is a connection between the two.

One experiment that was done to test the theory that links déjà vu to memory involved creating virtual reality scenarios based on the world of the video game Sims. Many who participated in the project ended up having various déjà vu experiences tied to scenes resembling similar ones viewed earlier.

Some people feel that déjà vu may help them predict a future event. But the experiment found that individuals didn’t become more likely to guess the correct path or come up with more accurate answers while playing out the virtual reality scenarios. More research is being done to figure out exactly why people have feelings of déjà vu.

Attention

When your attention is divided, you might take in certain details of a situation subconsciously, or without realizing it. When you start to pay full attention, those details seem familiar, even though you weren't aware you were taking them in. That may create a sense of déjà vu.

Most people experience déjà vu with no adverse health effects. In rare cases, déjà vu can be a sign of a neurological disorder. Individuals with epilepsy often have focal seizures that occur in one area of the brain, sometimes in the temporal lobe where we store memories. These are called temporal lobe seizures.

Seizures involve bursts of uncontrolled electrical activity that cause nerve cells in your brain to misfire. The shortness of focal seizures and the fact that people typically remain awake when they happen make it hard to recognize what's happening. People may mistake a person having a focal seizure as daydreaming or staring off into the distance.

Temporal lobe seizures can produce feelings of déjà vu. Signs that you may be having a temporal lobe seizure vs. a regular déjà vu experience include:

  • Sudden, unexplained feelings, such as joy or anger
  • Problems controlling your muscles
  • Twitching in your muscles
  • Having sensations that involve vision, taste, smell, hearing, and touch
  • Feeling as though you are about to have a seizure

Temporal lobe seizures impact your ability to interact with other people. Most of them last anywhere from 30 seconds to minutes. You may lose awareness of your surroundings or realize that you’ve been sitting and staring off into the distance. Others may observe you smacking your lips or constantly chewing and swallowing during the seizure.

Once the temporal lobe seizure ends, you may feel confused. It may be difficult for you to speak or remember what happened while having the seizure. A temporal lobe seizure can become a more serious tonic-clonic (or grand mal) seizure that causes convulsions and makes you lose consciousness.

You should get an evaluation from a doctor if you suspect that temporal seizures or other neurological issues may be causing your feelings of déjà vu. Get help immediately if you:

  • Have seizures lasting longer than 5 minutes
  • Have trouble gaining control of your breathing after a seizure
  • Remain unconscious after having a seizure
  • Have a second seizure after the first
  • Have other medical issues such as diabetes
  • Are currently pregnant
  • Hurt yourself during a seizure‌

Seek advice from a doctor if this is your first time having a seizure. Ongoing temporal seizures can shrink the hippocampus, the part of the brain that helps you learn and control your memory. You can also lose brain cells, leading to other memory issues.

Déjà vu is the false sense that you've witnessed a situation before. About two-thirds of people will feel it at some point. Scientists aren't exactly sure what causes it, but they believe it happens because of the way our brains process and retrieve memories. In some cases, it's a symptom of a neurological problem such as epilepsy.

What does déjà vu actually mean?

Déjà vu is a French expression, and it means "already seen."

What causes déjà vu?

Studying this phenomenon is tricky because a researcher can't stop a person in the middle of a déjà vu experience to examine their brain. But research suggests déjà vu is related to the ways our brains process information, and the way we make memories and recall familiar information.

Is déjà vu real or an illusion?

Scientists believe déjà vu is real, though the reasons for it are not well understood.