Like a night club magician uses slight of hand to fool his audience, our brains play mischievous tricks on us—no top hat or wand required. The magic word is not “abracadabra,” or “alakazam,” though. It’s a French term, actually: déjà vu. You’ve probably experienced it before, walking through the park, having a conversation, or plugging away at work, when—all of the sudden—a poignant feeling of familiarity strikes, yet you know the present moment to be original. How does the mind dupe us so easily? Well, neurologists are still trying to figure that out.
Meet the Experts: Dale Bredesen, M.D., neuroscience researcher and neurodegenerative disease expert in Novato, California and Meredith Broderick, M.D., a sleep neurologist and member of Ozlo Sleep’s medical advisory board.
So what is déjà vu, really? Here’s what we know, according to experts.
What is déjà vu?
In French, déjà vu literally means “previously viewed,” explains Dale Bredesen, M.D., neuroscience researcher and neurodegenerative disease expert in Novato, California. Medically, it refers to a feeling of familiarity with a scene or event that you know you actually haven't experienced, despite feeling as if you have, Bredesen adds. “In other words, it is a false feeling of familiarity,” he says. Around 97% of people have experienced deja vu at least once in their lives.
What does déjà vu feel like?
“Part of your brain’s memory capability is to distinguish novel situations from recognized ones,” Dr. Bredesen explains, such as the ability to tell a familiar path home from one you’ve never taken. Déjà vu interrupts that ability, and that learned feeling of familiarity is wrongly triggered by an unfamiliar stimulus. “But you still feel that wave of recognition, just as you would on a familiar path,” adds Bredesen. “It is often confusing, because you then start to look around and realize that, although it feels as if you’ve been here before, you can’t remember when or under what circumstances.”
Meredith Broderick, M.D., a sleep neurologist and member of Ozlo Sleep’s medical advisory board adds that some people described déjà vu as recognizing a situation, “but also a feeling that it’s not possible.”
Types of déjà vu
While the term déjà vu is used to generally describe the sensation of false familiarity, according to Déjà Experience Research, there are more specific terms to describe various types of déjà vu that encounter different senses or actions, like:
Déjà entendu: already heard
Déjà éprouvé: already tried or attempted
Déjà fait: already done
Déjà pensé: already thought
Déjà raconté: already recounted or told
Déjà senti: already felt emotionally
Déjà su: already known intelectually
Déjà trouvé: already met
Déjà vécu: already lived through
Déjà voulu: already wanted
Déjà vu causes
Experts haven’t quite nailed down the mechanism that causes “common” cases of déjà vu, Dr. Broderick says, but they appear to be linked to a false activation, or inappropriate “neuronal firing” within the brain’s temporal lobe, Dr. Bredesen explains—specifically, within the hippocampus, “a seahorse-shaped part of the brain that is involved in memory,” he adds. This misfiring can be caused by stress, lack of sleep, and some medications like benzodiazepines.
In more serious cases, frequent episodes of déjà vu have been linked to head trauma, brain tumors, dementia, and seizures as a sign of temporal lobe epilepsy, Dr. Broderick says.
When to see a doctor about déjà vu
“Having déjà vu occasionally—a few times a year—is not cause for concern, but having it frequently, or having it accompanied by other symptoms such as headache, shaking, or confusion or loss of awareness, means that there may be an underlying problem, and therefore you should be evaluated by a neurologist,” says Dr. Bredesen.
Dr. Broderick adds that seizure-related déjà vu, specifically, is often longer lasting and might come with out-of-body feelings and hallucinations, which is a definite red flag to seek help.
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