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Seeing into the future? The neuroscience of déjà vu
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Jordan Gaines
Pennsylvania State University USA

A blog on biology, psychology, cognition, learning, memory, aging, and everything in between. Explaining recent discoveries in neuroscience, translated to language we can all understand!

My posts are presented as opinion and commentary and do not represent the views of LabSpaces Productions, LLC, my employer, or my educational institution.

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Sunday, February 26, 2012

Even the most rational of us experience it: you'll be chatting with friends or exploring a place you've never been when suddenly a feeling washes over you: you've experienced this exact moment before. The familiarity is overwhelming, and it shouldn't be familiar at all. The sensation becomes stronger before ebbing, then completely leaves, all within a matter of seconds. Had you predicted the future? Yet, chances are, you can't pinpoint exactly when you'd experienced that premonition before.

Déja vu is a French term that literally means "already seen" and is reported to occur in 60-70% of people, most commonly between the ages of 15 and 25. The fact that déja  vu occurs so randomly and rapidly—and in individuals without a medical condition—makes it difficult to study, and why and how the phenomenon occurs is up to much speculation. Psychoanalysts may attribute it to wishful thinking; some psychiatrists cite mismatching in the brain causing us to mistake the present for the past. Still, parapsychologists may even believe it is related to a past-life experience. So what do we know for certain about what happens during an episode of déja vu?

Some researchers speculate that déja vu occurs when there is a mismatch in the brain during its constant attempt to create whole perceptions of our world with very limited input. Think about your memory: it only takes small bits of sensory information (a familiar smell, for instance) to bring forth a very detailed recollection. Déja vu is suggested to be some sort of "mix-up" between sensory input and memory-recalling output. This vague theory, however, does not explain why the episode we experience is not necessarily from a true past event.

A different but related theory states that déja vu is a fleeting malfunctioning between the long- and short-term circuits in the brain. Researchers postulate that the information we take in from our surroundings may "leak out" and incorrectly shortcut its way from short- to long-term memory, bypassing typical storage transfer mechanisms. When a new moment is experienced—which is currently in our short-term memory—it feels as though we're drawing upon some memory from our distant past. 
A similar hypothesis suggests that déja vu is an error in timing; while we perceive a moment, sensory information may simultaneously be re-routing its way to long-term storage, causing a delay and, perhaps, the unsettling feeling that we've experienced the moment before.
One characteristic is common of all déja vu experiences: we are completely conscious that they are occurring, implying that participation of the entire brain is not necessary to produce the phenomenon.
Over the years, researchers have pinpointed disturbances of the medial temporal lobe as the culprit behind déja  vu. Studies of epileptic patients investigated via intracerebral electrodes demonstrate that stimulation of the rhinal cortex (such as the entorhinal and perirhinal cortices—structures involved in episodic memory and sensory processing) can actually induce a déja vu episode.
Ventral (bottom) view of the brain, showing the perirhinal (red) and entorhinal (yellow) cortices.
A study published in the current March issue of Clinical Neurophysiology analyzed the patterns of electroencephalography (EEG) signals from the rhinal cortices, hippocampus (involved in memory formation), and amygdala (involved in emotion) in epileptic patients for whom déja vu could be induced by electrical stimulation. 
The researchers (from France!—who better?) found that synchronized neural firing between the rhinal cortices and the hippocampus or amygdala were increased in stimulations that induced déja vu. This suggests that some sort of coincident occurrence in medial temporal lobe structures may "trigger" activation of the recollection system.
While the cause and precise mechanism of déja vu remains a mystery, worry not—if it happens, nothing is wrong with you. In fact, bask in the moment and appreciate the strange feeling that washes over you. Or pretend to be a fortune teller. 
"It's like déja  vu all over again." 
-Yogi Berra, on witnessing Mickey Mantle and Roger Maris repeatedly hit back-to-back home runs in the early 1960s Yankees' seasons.

Photos courtesy Michelle Winnie and UCL.

Bartolomei F, Barbeau EJ, Nguyen T, McGonigal A, Régis J, Chauvel P, & Wendling F (2012). Rhinal-hippocampal interactions during déja vu. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology, 123 (3), 489-95 PMID: 21924679

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Or we are living in the Matrix...nah!

Very nice blog post (and I like the shoutout to french people!)

Deja Vu is also a nice way to explain to non-medical/scientist people about several theories of conciousness (different modules aggregating into one narrative, etc), because it is a phenomenon that most people have felt.


Cynthia McKelvey
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Very interesting article!

I'm just a little curious if you could elaborate more on what you mean by "One characteristic is common of all déja vu experiences: we are completely conscious that they are occurring, implying that participation of the entire brain is not necessary to produce the phenomenon."

And might this be a start on a series of dissociation disorders? That would be fun :)

Cynthia McKelvey
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Oops! I meant a series on* dissociation disorders. I hope you won't be falling prey to any dissociation disorders haha.

Jordan Gaines
Pennsylvania State University
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Thanks for the comments!

Cynthia, you know how during a deja vu episode, almost from the moment it starts, you're thinking in your head, "I'm having deja vu, I'm having deja vu" over and over until the feeling passes? You're completely aware it's happening. Compare that to having a dream: the weirdest things can be going on, but you don't realize it until you wake up and think, "Huh, a tapdancing narwhal..." Deja vu must leave some of our higher consciousness and awareness processing alone in the cortex, so the fact that it may be happening in somewhere like medial temporal lobe could make sense.

Cynthia McKelvey
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Ah, gotcha. Neat!

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