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February 26, 2012

Seeing into the future? The neuroscience of déjà vu

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.

Déjà 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 déjà 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 déjà vu?

This post was chosen as an Editor's Selection for ResearchBlogging.org
Some researchers speculate that déjà 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. Déjà 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 déjà 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 déjà 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 déjà 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 déjà 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 déjà 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 déjà 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 déjà 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 déjà 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 déjà 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 déjà vu. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology, 123 (3), 489-95 PMID: 21924679

3 comments:

  1. I thought this was settled. Didn't you watch The Matrix?

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  2. I am trying to understand why I have dreams from as far back as when I was in high school that are so vivid that when Deja vu happens it's the moment I dreamed about forever ago in complete detail happening years later. Or when I have an "episode" ( I am an epileptic patient) that I see objects or visions and then months or years later it finally happens in real life? When I am under a lot of stress I have visions that are very short and fast of objects, colors or surroundings that I haven't come in contact with yet and then later down the road I finally see it happening or that moment that I have already experienced in my "brain" like seeing the future. Usually it is a smell that is familiar but I can't put my finger on it that triggers my visions to happen in real time. A smell that I have smelled before or that I have come in contact with that takes me back or even forward. Can anyone explain why if the visions I am having haven't happen in my life yet, why can I see them in great detail months or years before they have even happened?

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    1. I often feel just like you, but with a twist. I have deja vu quite often, and I'm so very very sure that I experienced it before, just like you say - like it's a memory. There's no doubt in the moment. Unfortunately it's also almost always accompanied by a feeling of imminent doom - like I am remembering this now because it happened before - almost like I died and am reliving the same life, and remembering something right before I died. I'm so sure of my upcomming death that I immediately panic, but a minute later I remember that this happens to me quite often and I never die, and the fear goes away.

      I only found this blog tonight because half an hour ago I was reading a comment thread on a tech blog. The comment set it off and of course I knew for sure when I read the next comment and it was also familiar, that I was going to die tonight unless I got out of this situation (I'm on an offshore platform at the moment which didn't help my anxiety in the least during that 'episode').

      I suspect that if wasn't getting the same "death warning" every time that I would be as confused as you. I now attribute your situation and mine as the shortcut around short term memory (7 items or groups for 13 seconds) she was talking about in her post; the brain is putting new information in the "years ago" part of the long term (actually committed to) memory folder, and it feels like a confusing old memory. It happens all the time, but for the life of me I can never ever remember a time or place where I had the memory in the past. I just feel like I did; my brain really believes it did, with no evidence except that feeling.

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