How exactly does this work???
Mostly agree with Nautica, but I think that psychology also plays a big role. It is possible that in many cases, dejavu is the result of our mind forming a "false memory" of events currently occuring. Possibly a bit of crossed wiring between the patrs of the mind dealing with experiencing and remembering?
Whoooops! You happened to have asked about one of my favorite subjects. This will be long:
The brain event that causes the experience of a deja vu is in something called by neurologists a simple partial seizure. In general terms a seizure is anytime that a group or circuit of neurons begin to fire uncontrolably, and in synchrony with each other. Such activity can be limited to a very small part of the brain, or it can hit the whole brain, and anything in between can happen.
There is a part of the brain called the hippocampus that plays a vital role in the storage of memories.
If a person has a seizure limited to the hippocampus/hippocampal gyrus region it can trigger the persons physiology to experience an abnormally exaggerated response of familiarity to what is in fact only normally familiar. The hippocampus doesn't merely store and retrieve memories, it is responsible for orchestrating an appropriate emotional response to them. It tells us how familiar something is. Usually it does this so perfectly we don't even realize it is something that needs doing. When the hippocampus is under the influence of a surge of uncontrolled neuronal firing the result is a sense of hyperfamiliarity that gets erroneously projected onto the environment, or onto what we are thinking about; whatever is in our attention.
A seizure can also do the opposite in the hippocampus: flood it with an uncontrolled flurry of signals telling it to shut down. When this happens the person has the more rare and more bewildering experience of a jamais vu (French: "Never Seen") during which the environment, no matter how familiar, suddenly lacks any sense of being familiar at all. Everything in the person's field of view seems strange, lacking in reality, like a movie set that is a perfect imitation of the original but without any "authenticity" to it.
Neurologists specializing in seizures have known the cause of deja vus for decades. They are perhaps the single most common type of seizure there is. Many people with epilepsy have deja vus as the precursor to more severe types of seizures. They know the feeling of deja vu as the "aura"that warns them they will soon have something worse. The deja vu, in this case, is, in fact, the start of the seizure which then spreads from the hippocampus to include larger parts of the brain.
Studies have shown that over 50% of the population will have at least one deja vu during their lifetime. This is because the hippocampus is one of the very touchiest parts of the brain. It's seizure threshold can be lowered by lack of sleep, bad diet, stress etc.
French and Canadian researchers have actually made Electroencephalogram recordings of deja vus as they happened by means of depth electrodes placed through holes drilled in the scull into the hippocampuses of epileptics being prepared for brain surgery. The pictures of these EEGs I've seen are astonishing: a mildly wavy line starts suddenly to scribble back and forth rapidly at ten times the amplitude o the normal signal, as the hippocampus experiences this surge of hypersynchronous firing.
Some people who have no diagnosed seizure disorder find that they have "alot" of deja vus. One possible reason would be a history of childhood fevers that did minor damage to the hippocampus making it more prone than most to simple partial seizures. There wouldn't be any point in going to a neurologist about this unless it was happening so much it was driving you nuts, or if other things started happening like you noticed you were missing big chunks of time with no explanation. The latter could mean you were developing complex-partial seizures with a defect of consciousness and amnesia for the episode.
Deja vus are also sometimes a part of migraine "auras". There is an overlap between migraine and seizures where one disease blends into the other and sometimes neurologists have a hell of a time diagnosing which a patient actually has, if there is an actual difference. Fortunately the same medications are used for both.
That's the conlusion I had as well.. from my own experiences with dejavu. It appears as if I am recalling the memory as soon as it is stored... kind of like streaming mp3 files
Yes, but why does the seizure happen, in first place?
I tend to associate Dejavues with critical situations, even if my conscient part of the brain is not aware of the criticallity. Scaping from a girl, joining to other, or just to walk near a dangereus cliff are potential sources of dejavu.
In most people's cases it would be caused by a temporary lowering of the seizure threshold due to bad diet, not sleeping enough, or not well enough, and or stress. In chronic cases you would expect physical damage to the hippocampus, most commonly hippocampal sclerosis, or a progressive neuronal condition called "mossy fiber sprouting". These are the two most common hippocampal problems that lead to chronic seizures. Anything that causes a lesion or neuronal damage can become a seizure focus.
The single most common seizure trigger (trigger, not cause) is stress, emotional or physical. This would be in line with your experiences. Another really bad thing for anyone prone to seizures is alcohol. This lowers the seizure threshold alot.
Well, actually alcohol, bad diet (excesive) and lack of sleeping should fit better with me than stress...
As physicist (this is physics forums, is it?) I even developed a internal religious belief based upon Everet many worlds: the DejaVu situation marks a bifurcation in your life, so strong that the quantum collapse is to be perceived via the dejavy feeling.
Of course it is excessive to apply quantum collapse to macroscopical bodies, but it is a very marketable belief to say that even if you are suffering in this life-path, another "yourselfs" are following the other life-paths that bifurcated away this one. I could try to sell it to a sect :-)
There is a psychiatrist or psychologist who started his own clinic exclusively devoted to studying the phenomenon of deja vu, but I was alarmed and disappointed to find out it had taken a turn into pseudoscience. He doesn't seem to have found out they are seizures, and that this has been proven beyond doubt.
The experience is so strange and powerful for most people that it begs to be theorized about and thought about. Some believe it is a result of being reminded of something we knew in a past life, and use it as an argument in favor of reincarnation. Others believe it results from having seen the future in dreams, so that when the dream comes to pass it is completely familiar. Your many worlds/bifurcation theory is as valid as any of these in the absence of the proven neurological explanation.
What bothers me alot is that there are neurologists still offering theories about it being the result of an accidental mis-storage of short term memory in long term memory, so that when it is recalled a moment later it has the feel of being from somewhere much further in the past.
That is perfectly logical, but it demonstrates that these researchers haven't done even the most basic reviews of the existing literature on the subject in their own field.
Another school of neurological researchers is theorizing that it is the result of an accidental time delay between one hemisphere communicating with the other.
Again, it is a logical train of thought, but I don't understand why they haven't reviewed the literature where they would find that deja vu is the single most frequently experienced simple partial seizure symptom of all, and where they would have run across the often cited, well known paper: Anatomical origin of déja` vu and vivid `memories' in human temporal lobe epilepsy 1994 or the much earlier paper The Role of the Limbic System in Experiential Phenomena of Temporal Lobe Epilepsy 1981, both of which show EEG recordings, picked up by depth electrodes, of paroxysmal activity in the hippocampal region while the patient reports being stunned by the feeling of deja vu.
These two latter theories (mistorage in long-term memory, and, inter-hemispheric delay) have been repeated alot, sometimes being mistaken for proven explanations. I guess they are easier to grasp, and potentially less upsetting to people who would balk at the suggestion that theyve had any kind of seizure, no matter how unimportant that is when you're talking about an infrequent seizure on this very small scale.
Despite that, these non-seizure theories are unprovable and unessesary in the presence of the proven seizure phenomenon.
Seizure-fearing types often say that just because the seizure kind is proven doesn't mean other kinds don't exist. True, strictly speaking, but an irrational reaction to the proven explanation isn't really a good reason to decide a less upsetting sounding explanation must exist and be found.
The phenominon can also be triggered by certain EM fields. This has been reproduced in the lab.
Makes perfect sense, although I haven't seen anything about this before. Is this related to Persinger's ongoing studies of EM fields on the brain?
But zooby, just because a type of "dejavu" feeling has been found in people diagnosed with temporal lobe epilepsy, it doesn't mean that anyone experiencing what they describe as "dejavu" is having a seizure. That would be like telling someone with a cough that they have tuberculosis because it has been medically proven that a symptom of tuberculosis is a cough.
That's like saying - Why look for any other reason for the cough when you know for a fact that tuberculosis can cause it?
I don't know anyone that has not experienced "dejavu". Are you saying that the entire population of the earth is having seizures?
No. Your comparison is way off. The lungs are nothing like the hippocampi.
I've met many people who have not had deja vus. When I describe them, these people have no idea what I'm talking about. They think you are exaggerating about one situation reminding you of an actual similar situation. Polls I've read come up with figures between 30 and 50 percent of the population reporting they have had a deja vu.
People who have a deja vu are having a simple partial seizure, yes.
This will only seem outrageous if you get hung up on the word "seizure", because to most people that means falling to the ground unconscious and having uncontrolable convulsions.
The word "seizure" is used by neurologists to refer to any incident of hypersynchronous firing of neurons that is not part of the brain's normal functioning.
When this activity is limited to a very small part of the brain, only those functions controlled by that part of the brain are affected. In the case of the hippocampus seizure activity produces this surge of "familiarity" above and beyond what the person realizes is appropriate. This is not anything to get the least bit upset about (unless it becomes chronic.)
So, yes, all those people who have had a deja vu have had a seizure, but it is just the very tiny, unimportant kind. Nothing to get upset about.
If a person has chronic deja vus a neurologist can prescribe an anti-epileptic drug that will drastically reduce the number of them. Now if it were a common thing for a doctor to try all the A.E.Ds on a patient with no success, THEN I would suspect there must be some other cause of deja vu's that is non-seizural.
Do you have a link or refference to one of these polls? I find that number astonishing, I don't believe I've ever met a person who has never experienced dejavu.
Are you sure you're not reffering to the number of people who've never been to DejavuTM?
I do not have a link. I didn't save any of these so I will have to dig around for you.
What is Dejavu™? Is that the strip club chain?
eMedicine Clinical Knowledge Base - Online Medical Journals, Textbooks, and Physician Reference Articles
has a vast collection of really good papers on epilepsy if your interested. You have to register but it's painless and free.
I can claim all of the above. Mostly STRESS.
You mentioned this in another thread, and what you said was dead on. Coincidence?
Zooby - explain how these "seizures" are non-consequential? They leave behind no damage? Also, I agree with Lurch, 30-50% has to be WAY too low.
Non-consequential isn't completely accurate. A few deja vus over the course of a person's life time won't do any percievable damage. Nothing you would have to worry about in the least. The main thing to worry about is the fact that seizures teach the neurons to seize. They are just that little bit more likely to do it the next time the seizure threshold is compromised.
Seizure activity itself doesn't damage the neurons that I have ever read. With big seizures, however, there is some evidence that there is a post-seizure starvation of blood flow to selected areas. This can potentially kill more neurons.
Well, name your percentage and I'll endorse it. In fact, even if we stipulate for the sake of argument that 100% of people will have at least one deja vu before they die, it still can't be used as an argument against them being simple partials. If you ask how 100% of people could have at least one seizure all I can say is why not? If the symptom is there, the hypersynchronous firing is there.
One thing that is important when you ask someone if they've had a deja vu, is not to use the term "deja vu", but to describe the sensation to them. A couple times I've found out that people who haven't actually had them will answer in the affirmative because the only understanding they attach to the term is the Yogi Berra understanding of the same problem coming up again. Since they haven't had a real deja vu, they don't have any conception of what it's like, and assume everyone is using it the way they understand it. Once you describe what you're talking about in detail, they have no idea what you mean.
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