What We Know About the Neurobiology of Deja Vu

We are all familiar with Yogi Berra's famous quote:  It's like deja vu all over again - but what exactly is deja vu?

I know for certain that every one of my readers has experienced it. How can I make such a bold statement? Many surveys have found that about two-thirds of adults report having at least one experience with deja vu. But my confidence comes from the finding that deja vu occurs most often in people with a well-developed, frequently-stimulated imagination. College graduates report more frequent deja vu experiences than less educated ones. Frequent travelers are more prone to it than people who prefer to stay home and watch TV. Hence my certainty that you, the reader of this post, have experienced it. Now that I pandered to your vanity, do you know

College graduates report more frequent deja vu experiences than less educated ones. Frequent travelers are more prone to it than people who prefer to stay home and watch TV. Hence my certainty that you, the reader of this post, have experienced it. Now that I pandered to your vanity, do you even know what is deja vu?

Deja vu’s footprints in history and literature

I am sure we have all read the 5th-century writings of St. Augustine. But in case you forgot, he alluded to deja vu when he wrote about “falsae memoriae.” And so did Sir Walter Scott (who hasn’t read Ivanhoe and Rob Roy?), Charles Dickens, Proust (everybody reads him, no?), Tolstoy, and many others. In fact, novelists and poets have described deja vu much better than scientists did. Partly, because they are simply more eloquent. And partly, because this group actually experience deja vu much more frequently than the general population.

There are other interesting historical tidbits. Several religious Saints earned their “degrees” for having premonitions, visions, and prophecies based on good old deja vu. And not to single out Catholicism, deja vu was invoked in religions like Hinduism and Buddhism as evidence for past lives. The path from here to outright fraud is quite slippery. Innumerable charlatans have claimed clairvoyance based on deja vu.

What is deja vu?

As the French name (“already seen”) implies, it’s the fleeting sensation that a scene or an object is vaguely familiar, you feel like you have experienced it in the past, but you aren’t exactly sure when or where. You can’t say for certain if you were present at the scene or not. But you still have that feeling of familiarity.

When it comes to psychological phenomena, who but Freud had a ready explanation? Deja vu, he said, is evidence of unconscious conflict, the ego defending itself against upsetting erotic urges for a mother figure or other hidden desires. Today we can safely dismiss his theory as, well, BS. Deja vu occurs in people with perfectly normal psyches and brains, conscious and unconscious. It almost never occurs before the age of 8, slowly increases in frequency up to the 20’s or 30’s and then slowly declines until it is virtually unknown in people in their 70’s. It occurs more frequently in people who are stressed or exhausted after a long day of work, especially mental work. Here is a clue: we also know that memory is impaired in states of fatigue. So is it possible that something related to memory processing is involved?

Deja vu occurs in people with perfectly normal psyches and brains, conscious and unconscious. It almost never occurs before the age of 8, slowly increases in frequency up to the 20’s or 30’s and then slowly declines until it is virtually unknown in people in their 70’s. It occurs more frequently in people who are stressed or exhausted after a long day of work, especially mental work. Here is a clue: we also know that memory is impaired in states of fatigue. So is it possible that something related to memory processing is involved?

What’s going on in the brain?

Memories are processed and stored in and around a sea horse-shaped organ in the brain appropriately called the hippocampus (seahorse in Greek). It is located in the medial (inner) part of the temporal lobe. A severe blow to the side of the head, where the temporal lobe is located, can wreak havoc with memory, ranging from disorientation to time and place all the way to global amnesia. Since deja vu is, in essence, a memory phenomenon, shouldn’t we look to the temporal lobe and the hippocampus for answers?

Indeed, the sensation of deja vu often precedes temporal lobe seizures. But temporal lobe seizures do not occur commonly enough to explain the phenomenon.

Here we come to the limit of our knowledge. Neuroscientists believe that deja vu is the result of temporarily overactive circuits in the temporal lobe. But they don’t know for sure. A major problem in investigation of the phenomenon is its very ephemeral nature and its unpredictability. After all, you can’t wire people to an EEG and wait for them to have a deja vu experience; they might have to have those electrodes stuck to their skull for years.

 

The prevailing theory today

The prevailing theory today is that deja vu is a result of overactive circuits in the temporal lobes. We know this phenomenon in our daily life: a surge in the electrical circuits causes the computer to shut down, or the circuit breaker to shut off, or the generator to shut down. Now imagine an infinitely more complex electrical circuit. A single neuron has more connections to neighboring neurons then the whole electrical system of PG&E, our disruption-plagued utility. So is it any wonder that every once in a while some of the neurons get temporarily out of whack? Would that PG.& E’s blackouts last only a few seconds? In fact, the more we learn about the enormous complexity of the brain, it gets more mind boggling, so to speak, that it functions as well as it does.

Specifically, what may be happening to create the deja vu illusion? In the normal course of events, when the retina captures a certain scene, the “pixels” of the picture are converted into electrical signals, transmitted via the optic nerve to the visual cortex, processed there and then transmitted to way stations in other regions in the brain, including the temporal lobes. Once the scene is reconstituted to the “original” it is forwarded to the prefrontal cortex, or to our consciousness. Now imagine a short delay in the transmission from the temporal lobe way station to the prefrontal cortex. In psychological terms, the scene is already imprinted in the subconscious but is delayed for a fraction of a second before it reaches the conscious. A vague sense of familiarity ensues.

Of course, this is only a plausible hypothesis, not evidence-backed theory. And in a way, that’s good. I like the fog-shrouded, ambiguous picture of deja vu. It has inspired writers and poets to great heights of imagination. It lent the brain the aura of mystery. But inevitably, one day the bright light of knowledge will shine on it and the magic will evaporate.


This post was reviewed and updated on 5/5/17.

Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.

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