How science explains déjà vu and when it worries – 5/8/2023 – Science

Have you ever moved to a new place and felt like the place was familiar? Or did you have the feeling that you knew someone that you were actually seeing for the first time? If so, you can count yourself among those who have had déjà vu.

In 1876, Émile Boirac, a French philosopher and researcher, coined the term, which means “already seen”. But since Plato, who saw experience as proof of the existence of past lives, intellectuals have tried to explain the phenomenon.

The psychoanalyst Sigmund Freud, for example, described déjà vu as an “unconscious fantasy memory allied with the desire to improve the current situation.” Carl Jung, in turn, theorized that there was a relationship with the collective unconscious.

“There’s nothing supernatural about it, and it’s extremely normal to experience déjà vu,” says James J. Giordano, professor of Neurology at Georgetown University in Washington DC, USA.

“Déjà vu is literally a person’s subjective experience of repeating a particular set of events, activities, thoughts and feelings, even though this has never occurred before,” said Giordano.

About 90% of people experience the phenomenon of déjà vu. The frequency, however, decreases as we age.

mystery to science

“Our brain basically works like a space and time machine,” Giordano tells DW. “It takes everything in our present and relates it to something similar or different in our past. That way it will be able to plan for the future. But there’s a possibility that these signals get mixed up.”

Giordano suggests that the phenomenon has to do with a region in the middle of the brain called the thalamus. All information, such as hearing, taste, touch, etc., passes through the thalamus to reach the cerebral cortex (the outermost layer of the brain). This information is subsequently processed.

The cerebral cortex is the layer of the brain popularly known as “gray matter” and is responsible for thoughts, voluntary movements, judgment, language and perception.

“If the speed of these interactions is slightly different, it’s like we remember the present. So what our brain does is literally confuse the present with the past,” Giordano explains.

Roderick Spears, associate professor of migraine research and clinical sciences at Brown University in Providence, Rhode Island, agrees that there isn’t a solid explanation for why and how déjà vu happens.

A window to a parallel universe?

“It’s difficult to study déjà vu because it’s spontaneous. We don’t know how to trigger episodes like this in a lab,” says Spears.

Over the decades, scientists have come up with a variety of theories about why and how déjà vu happens.

A popular theory with a neurological perspective is dual processing—in which information is stored and retrieved through different processes in the brain.

For example, you are sitting in your living room reading this article. The smell of your mother’s cooking is in the air, your pet is snuggled on the sofa, you hear the notification sound on your cell phone and you feel the warmth of the sun on your skin. All these sensations add up during processing in the brain and are interpreted as a single event.

According to dual processing theory, when there is a slight delay in the brain while processing one of these inputs, it interprets the experience as two separate events, giving the feeling of familiarity.

There are also studies that relate déjà vu to a supposed parallel universe. Theoretical physicist Michio Kaku believes that déjà vu is a kind of memory failure that occurs when “fragments of memories stored in the brain are triggered when moving into an environment that resembles something we have already experienced”.

But he also theorizes about the possibility of switching between different universes — and whether déjà vu could be trying to tell us something about our position in those universes.

Déjà vu as a symptom of stress

There are also studies suggesting that stress can be a factor in déjà vu.

“The brain works best when it’s rested and energized. When you’re under excessive stress, or with a lot of worries, the brain gets tired. So what can happen is the pattern of brain activity changes a little bit. With that, it’s not uncommon. experience a déjà vu”, explains Giordano.

Spears adds that highly educated people tend to have déjà vu more often. “People who travel a lot, who remember their dreams and people who have liberal beliefs may experience this more often,” she points out.

Cause for concern?

Is having deja vu a sign of a sick brain? “No way,” said Giordano. Déjà vu happens to healthy people all the time and is most common between the ages of 15 and 25.

But Spears advises anyone who experiences this more than a few times a year — say, several times a month — to seek medical attention.

He further notes that if déjà vu is associated with loss of consciousness or an abnormal dream state, it could be a symptom of something serious.

“Things to look out for include experiencing déjà vu for more than a few seconds or having difficulty distinguishing between what’s real and what’s not. Or you may notice someone developing unconscious behaviors like playing with their hair or not being able to of holding objects in your hands. Also, an increased heart rate or an overwhelming sense of fear should prompt a medical evaluation,” says Spears.

In rare cases, déjà vu is a sign of a seizure, specifically an epileptic seizure. “The temporal lobe is where most seizures come from. It happens when the lobe is overactivated and the person is semiconscious, but not completely unconscious. This can produce a feeling of déjà vu”, explains the specialist.

While there’s a broad consensus on what it’s like to have déjà vu and several theories about what causes it, scientists still don’t have a definitive answer when it comes to this strange feeling.

“We still don’t have a solid structural explanation,” says Spears.