[INTRO ♪].

Hopefully, you have never had a near-death experience. But if you have, I'm glad that you survived it.

Uh, also, maybe this sounds familiar: A blinding white light. Your life flashing before your eyes. Floating out of your body and looking down on that body from above.

Honestly, it might sound familiar either way. At this point, the near-death experience is a bit of a cliché in pop culture— but this stuff really happens. Near-death experiences are most likely caused by a bunch of different processes, and scientists are still figuring out all of the mechanisms.

But either way, these experiences probably aren't as mystical as they seem. There are accounts of near-death experiences going back to ancient Greece, and because modern medicine can bring people back from the brink of death more often, they're even more common now. What's weird is that most people who have them report seeing the same kind of stuff.

The white light. The out-of-body experience. A sense of peace.

An awareness of being dead. The experiences are so universal that there's actually a standardized questionnaire to evaluate whether or not someone has had a near-death experience. But when it comes to understanding why they happen, things are less clear.

For one, there's virtually nothing medically, demographically, or psychologically different about the so-called “experiencers” compared to non-experiencers who have also almost died. They're also just really hard to study. It's generally frowned upon to almost kill someone while they're in an fMRI machine.

Also, studies of near-death experiences have major sampling issues. Studies done after the fact rely on experiencers identifying themselves as participants, which can cause some serious bias. But other studies, like ones where experimenters waited on call for people to go into cardiac arrest, have a hard time getting enough participants for a good sample size.

Also, waiting around for people to start dying? Not a super-fun job. But even though they're hard to study, there are tons of ideas about what could cause these experiences— and they're probably not just caused by one thing.

One idea is that rather than experiencers seeing and feeling the same things because they're actually having similar experiences, they see and feel them because they expect to. This kind of thing happens all the time, like in eyewitness testimonies. People are pretty suggestible, so it's reasonable to think that the clichés about near-death experiences might impact what people actually see and feel during them.

Another view is that they are a psychological response to the threat of death. Beginning in the 1930s, psychologists suggested that these experiences were a result of depersonalization, where you feel detached from your identity and what's happening to you. Basically, you know you're dying, but you feel completely detached from it.

It's like it's not real. Among other things, that would also explain why near-death experiences cause calmness and peacefulness. More recent research has argued that dissociation, where your consciousness seems independent from your real, physical experience, is actually to blame.

Daydreaming is a totally normal example of this, but an extreme case is an out-of-body experience. And there's some evidence to back this one up. All kinds of trauma often result in dissociation, so there are tests to clinically identify it.

The tests ask responders to identify how often they do things like totally zone out while watching TV or have no recollection of an important event. A study from 2000 looked at 134 subjects who had come close to death, 96 of whom had had near-death experiences. They found that the experiencers scored much higher on the dissociation test, meaning they were more prone to mentally check out of situations.

It's also possible that near-death experiences could be entirely or partly biological, and there are a number of possible mechanisms that could explain the things experiencers see and feel. For instance, the combination of fear and depriving the optic nerve of oxygen has been known to cause tunnel vision. And, when faced with the extreme stress of dying, the brain probably releases all kinds of chemicals to protect itself, which can lead to those other weird symptoms.

A 2004 study showed that out-of-body experiences can be triggered by stimulating the right temporoparietal junction, a part of the brain that plays a role in processing information from your environment and in distinguishing between yourself and others. Experiments with an anesthesia called ketamine have also suggested that, under stress, the brain might release neurotransmitters that cause detached, dreamlike states or hallucinations. And other studies have shown that stimulating a part of the midbrain called the locus ceruleus can release noradrenaline, which is involved in fear and stress reactions and can alter your emotions and memories.

Both of those processes could be related to peaceful emotions, hallucinations, and that sense of your life flashing before your eyes. So it's possible that near-death experiences are caused by a combination of all of these factors, biological and otherwise. Of course, there are critics of these studies—and they make a good case.

They argue that, if these are normal biological mechanisms associated with the stress and trauma of death, why doesn't everyone who almost dies have them? We don't know. But for people who do have them, there are a whole bunch of scientific explanations for where they might come from.

And whether they're caused by biology, psychology, or something in between, near-death experiences can teach us a lot about how our brains work and that weird thing we call "consciousness." Thanks for watching this episode of SciShow Psych, brought to you by our patrons on Patreon. If you'd like to help support the show and help us keep making episodes like this one, you can go to patreon.com/scishow. We very much appreciate everybody who does that. [OUTRO ♪].