How do near-death experiences arise?

In past times, if your heart stopped beating, that probably meant that you wouldn't live to tell the tale. But modern medical techniques mean that many heart attack patients survive, and those who've been that near to death often say that they experience bright lights or other strange phenomena. Until now, doctors have struggled to understand why, but Jimo Borjigin looked into the question in a paper in PNAS this week.

Jimo - In the literature, what I find is 10% to 20% of cardiac arrest survivors had their near-death experiences. There are various kinds. They are not all identical, but there are some common threads such as seeing bright light. But I even think that that number is underestimation because a lot of people are afraid to speak up about their experiences. They're afraid to be ridiculed. They're not convinced this is really a supernatural, but yet, even science hasn't provided any answers. I might be biased, but I think our study might be really the first attempt and then I'm sure, many more will follow.

Kate - How do you go about investigating near-death experiences because obviously, when a human is having a near-death experience, we've normally got other things to worry about than measuring their brain?

Jimo - That's right.  eah, if I know if somebody is about to have near-death experiences, first instinct is to save them rather than to stick electrodes in their brain. So, I think to do that kind of studies for individuals with a cardiac arrest is really tough. Unless you know somebody is going to have a pre-scheduled brain operation and we could perhaps give them EEG, electrode recording, just in case that patients, when they wake up, they'll report some kind of near-death experiences. I think those might be the kind of more feasible studies one could perform in the future, if there are sufficient number of patients who actually are available for neurosurgeons to gather data from.

Kate - So, until we can get those human subjects, what subjects did you use in this study and how did you go about looking at this phenomenon?

Jimo - Well, rodents are standard animal models for our studies, whether it's rats and mice and that is just the reality of today's scientific research. So, what we did was just give them anaesthetics and make sure they're not sensing any pain. We gave them lethal injection to the heart to stop the heart. During this whole time, we monitor their brain activity by placing 6 electrodes in distant parts of the brain and the results were all published in the paper.

Kate - And far from the brain going quiet after death, it actually became quite active.

Jimo -  Exactly. So, that's what we were actually really surprised to find measurable activities. We were predicting maybe something comparable to the levels we would see when an animal is awake. But what we were really surprised by is how high those activities were. In fact, they're 5 to 8 times higher during the near-death state than the waking state.

Then I really remember that in the human near-death experience, one of the very common description of experience, is they're realer than real, hyper vivid, hyper lucid. I mean, to the patients who experienced that, they seem to be extremely real. I think that realness of that perhaps is reflected by these measures that we provided and that is still not clearly confirmed. We need many scientists to get involved in these kind of studies, so we have a more advanced understanding of this phenomena.

Kate - Was any particular areas of the brain involved in this activity, like if someone saw a bright light, was the vision at the parts of our brain involved in this activity?

Jimo - Well initially, since we hear a lot about bright light, my first instinct was, "Their visual cortex must be highly activated."  In fact, maybe visual cortex is the only part that is activated and that's what I thought naively initially. But I was surprised by how the entire brain seems to be participating in this amazing event, the electrical oscillation, not just occipital areas which is the visual cortex.

There is a unique sequence of events that every single animal demonstrates. There's different frequency at the different time period during this 30-second cardiac arrest. So initially, a very narrow band of high frequency activities and then eventually, it culminated really in the highly activated and not only in terms of the power density, but it's also in the coherence which is the synchronised firing of distant parts of the brain, mainly in the gamma range. Gamma actually expand a huge range in this case, anywhere from 20 to 25 hertz, all the way up to 250 hertz that were investigated in our studies.

Kate - Does this activity tell us anything about why these near-death experiences might happen? Some of us might presume that if the brain is going without oxygen, it would just shut down very quietly. Do we know why?  s the brain having like a last hurrah or a last gasp before it runs out of oxygen?

Jimo - Yeah, I saw that comment, but I think perhaps since we see it in rats and I predict we're going to see that in humans in the future, my guess, this is really brain's built in defence against lack of oxygen, lack of glucose. We all know that a brain is very plastic. So, if you do something to damage the brain, to injure the brain, brain actually mounts a defence against that injury and insult. So, I think this is perhaps one built-in mechanism against external threats and if there's a lack of oxygen or glucose, maybe just one of the ultimate threat to brain survival.