Out-of-body experiences, a bright light at the end of the tunnel: scientists can only speculate about what people experience when they die. What happens in the brain shortly before death, on the other hand, has now been well studied. The neurologist Jens Dreier explains in an interview how to investigate the physiological processes during dying – and what they have in common with strokes and migraine headaches.
Dreier, they explore the brain between life and death. How, do you think it feels to die?
Of course, it depends a lot on why you die. If we have no pain, we may not even notice the transition. It may then be the same as when falling asleep. Or we still have some kind of consciousness and are temporarily in a dream-like state, which we consider to be reality. That would be something like a near-death experience.
What scientific knowledge is there to experience death?
Our knowledge is based exclusively on interviews: people who have just missed death, for example because they were reanimated, report on their experiences. However, only very few have such memories, which is why the data situation is relatively thin. In research there is scales that you use to determine whether something was a near -death experience or not. However, I don't find this without any problems because the experiences can only be standardized. If someone reports on their experiences, you should take note of it in my opinion.
What are typical near-death experiences?
There are some recurring patterns, such as the feeling of being in different epochs at the same time. Often, abstract sensory impressions also arise, for example a light light or a narrowing of the field of vision - as if you were running through a tunnel. Some also tell of out -of -body experiences.
Comparable sensations sometimes occur in completely different situations.
Yes, this very rarely happens during surgical operations. One patient is in anesthetic and a critical situation occurs, such as a circulatory breakdown. Some then report on near -death experiences. But this can also occur in non -life -threatening situations.
For example?
You sit in the opera house and listen to an aria.
Suddenly they drift into dreams, which they experience as real.
Experts call this phenomenon rem-intrusion.
This is a sleep phase embedded in a wax phase that you do not perceive as such.
This happens particularly often in the clinical picture of narcolepsy.
is a professor at the Center for Stroke Research Berlin (CSB) and senior physician at the Neurological Clinic of the Charité. His research group investigates, among other things, strokes that occur after a certain form of cerebral hemorrhage, the subarachnoid hemorrhage. The investigations are part of the international co-operative Studies on Brain Injury Depolarizations (COSBID) and deal with so–called spreading depolarizations - large activity waves that arise in various brain diseases, but also in dying.
Nevertheless, one speaks of near -death experience here? There is a set of similar experiences that are defined by scales, but can occur in different contexts. They only really occur frequently with resuscitation. That is why one usually speaks of near -death experiences when one means these states of consciousness. The whole field has an anecdotal character, which makes scientific access more difficult. But the abundance of reports indicates that such experiences really exist. Incidentally, they also occur in different cultures and do not depend on certain religions. All of this suggests their existence, the physiological processes are examined during dying. What happens in the brain? Let's take the simplest case: someone suffers a cardiovascular arrest. A few seconds after the heart stopped, the oxygen concentration in the brain drops. The nerve cells switch to a saving mode, which massively throttled the neural activity. After about seven to eight seconds, the person concerned loses consciousness; After 30 to 40 seconds, the entire brain activity has gone out. However, the exact time depends on the extent of the remaining blood flow.
Are the nerve cells already dying then?
No. First comes a phase without activity in which the neurons are only inhibited, but are still alive. As soon as the blood circulation uses again, they work normally again. Experts call the state of hyperpolarization.
Can you explain this in more detail?
Nerve cells have so -called membrane potential, they are "polarized". The inside of the cell membrane is normally negatively loaded at the idle state; A voltage of –70 millivolt is due compared to the outside. You have to imagine it like a loaded battery. The cells depolarize during a nerve impulse. The inside is consequently positive for a short time in order to then repolarize again, that is, to return to the initial state. If the oxygen supply breaks off, the following happens: The cells hyperpolar. So you become even more negative than you already are. They can no longer be excited from this very negative state, although the battery is still fully loaded.
What happens then?
To maintain hyperpolarization, the cell still needs a bit of energy. The body normally produces these from glucose and oxygen. If there is no longer enough of them, the diaphragm pumps that generate the voltage gradient can no longer work. After a few minutes, a huge depolarization wave, also known as "terminal spreading depolarization", occurs, in which the nerve cells discharge one after the other, similar to a short circuit. We detected them in humans for the first time in 2018. The light phenomena shortly before death could be due to this pathophysiological process.
What parts of the brain does the wave pass through?
It usually begins at certain vulnerable points of the cerebral cortex and spreads over the entire brain at a speed of an estimated three millimeters per minute. It hikes through all areas in which the nerve cell bodies sit. In addition to the brain bark, this includes, for example, the basal ganglia, the cerebellum and even structures in the spinal cord.
Some also speak of a wave of death. Ultimately rang brain death?
In fact, it causes massive changes inside the nerve cells: all sorts of molecules are wildly jumbled together. For example, the concentration of calcium increases by 1000 times. If this lasts too long, the neurons get poisoned and die. However, the amazing thing is that they endure this state for a certain time. As long as the diaphragm pumps are put back in place and everything that does not belong inside is transported out, the cells survive.
When does the resuscitation have to be started at the latest so that the pumps jump back?
This depends on various factors, for example on the temperature and age. Let us assume that we have an otherwise healthy young person at room temperature. From cardiac arrest to the inserting of the nerve cell death, it takes an estimated five minutes. After just three minutes, the huge wave sets itself in motion. But as soon as someone reanimates, so press properly on the heart, body and brain are easily supplied with blood. Then the nerve cells last significantly longer.
How did you discover the wave shortly before death? To do this, you had to record brain activity at the exact moment when a patient died.
That was a coincidence. The real motivation for our research was to help people with a certain form of cerebral hemorrhage. Namely, the depolarization waves occur not only during dying, but also during strokes. With my team at the Charité in Berlin, I am investigating so-called subarachnoid hemorrhages. They arise when a bulging of a cerebral vessel bursts. Often the bleeding stops temporarily. Then neurosurgeons or neuroradiologists have the chance to close the bag securely, so that the risk of further bleeding is eliminated. Unfortunately, the patients are not over the hill yet. Because the clotted blood is now on the surface of the brain and often triggers strokes about a week later due to a lack of blood circulation.
And they wanted to track them down with their measurements?
Exactly. The patients are usually in a coma in the intensive care unit, where they can only be examined neurologically to a very limited extent. That is why these delayed strokes usually pass unnoticed. However, as with the dying process, the depolarization waves also occur here. If you record the neuronal activity with electrodes resting on the surface of the brain, you can tell from the waves if the person suffers a stroke. This allows us to intervene therapeutically in a timely manner.
That means that in the event of a stroke of the brain, the same thing happens in the brain as when dying?
Spreading depolarization follows similar principles to those shortly before death. An important difference is that the lack of energy in stroke occurs only locally, but globally in dying.
Similar to the near-death experiences, the depolarization wave also occurs in situations that are not life-threatening. Which are these?
One example is the migraineura. Here, among other things, scientists were able to observe how the wave spreads in the brain using functional magnetic resonance imaging. There was a very amusing background in a study from 2001: a team in Boston had an employee who always got a visual migraineura when playing basketball. He always had to go straight from the sports field to the scanner. So he was able to report during the MRI recording in which part of the field of vision he perceived the aura.
It is said that the wave of discharge before death is huge. Is she that big on migraines too?
Yes, it is much greater than any epileptic seizure - both with migraineura and shortly before death! In the former, however, it almost never leaves consequential damage.
The dying brain runs out of energy, so that the diaphragm pumps no longer maintain the voltage gradient and the »spreading depolarization« occurs. But why does this occur with migraines?
As already mentioned, with a stroke – when a blood vessel becomes clogged – the same thing happens as when dying, only locally. This is due to the lack of energy. Some of the migraine headaches could have the same cause: a small blood clot closes a vessel and triggers the wave. But it is so tiny that it dissolves again by itself and therefore does no harm.
A persistent foramen foramen (Pfo), a small hole between the two heart atmosphere, is more common in adults with strokes. Now studies indicate that migraines with aura also occur more often in people with pfo. That would support their theory to the cause.
Yes that's true. The hole creates a kind of short circuit: low-oxygen, venous blood flows directly to the other side of the heart instead of into the lungs and reaches the brain from there together with any clots. Sometimes we can even detect very small strokes after a migraine aura. Just recently we had such a case: A colleague of mine was sure that a patient's symptoms must be a migraine aura. As a precaution, we did an MRI and saw three dots in the brain, three tiny strokes. The only cause we found was an open foramen ovale.
So, could migraine be treated with aura by closing the hole in the heart?
You actually tried that. But apparently it does not work for all those affected, because there are many other triggers for the wave, which are largely not yet understood. For example, certain congenital disorders in the nerve cell or astrocyte metabolism go hand in hand with this migraine form, which has nothing to do with vascular problems. Incidentally, the process of "spreading depolarization" can even occur without a typical blood circulation: for grasshoppers and cockroaches, for example. He is very old.
Some believe that the discharge wave when dying could be the physiological counterpart to the visual phenomena in near-life life. Do we all have a major migraine aura before death?
I'd be careful about that. A colleague of mine at the University of Copenhagen used internet-based surveys to investigate whether people with migraine are more prone to near-death experiences. So there really is an association. However, these are only vague indications. My group from the Charité is currently conducting another study on the topic together with the Copenhagen team, this time on patients from the headache outpatient clinics. Unfortunately, the results are not yet available. But what may also help to clarify the nature of near-death experiences are certain drugs.
Why this?
There are substances that trigger exactly such experiences. The two most important are ketamine and dimethyl tryptamine (short: DMT). The interesting thing is that you inhibit the depolarization waves. In emergency situations, the body may relieve similar substances to prevent or delay the "spreading depolarization". The near -death experiences could go back to the effect of the "inner drugs" and not on the wave itself. Only the bright light would be an indication that parts of the brain are already affected by the wave. But of course that's pure speculation.
