A surge of brainwaves in two people who lay dying after their life support was turned off may help to explain the phenomenon of near-death experiences.

The sensation of moving down a tunnel towards a bright light, reliving memories, and hearing or seeing deceased relatives have all been reported by people from many cultures who have had a brush with death. Some scientists, however, say these experiences could be caused by hallucinations as people recover in the hospital. Now, we have identified brain activity that could be behind these experiences.

Ten years ago, Jimo Borjigin at the University of Michigan Medical School and her colleagues showed that rats have a surge of electrical activity in their brains as they die. To look for the same thing in humans, the team combed through anonymized medical records for people who had an electroencephalogram, or EEG, recorded as their life support was switched off because they had no hope of recovery, finding four such people.

These people were critically ill in intensive care units and had electrodes placed on their heads to monitor their brainwaves for signs of epileptic seizures.

Studying this data allowed the team to investigate what was happening in dying brains. Brainwaves can be seen on an EEG when large numbers of brain cells fire together in synchronized cycles. These waves can happen at different frequencies.

Previous work suggests that faster frequencies, known as gamma brainwaves, are a hallmark of consciousness, higher thought processes, and memory retrieval. This is particularly true if they occur in two areas on each side of the head, known as the temporal-parietal-occipital (TPO) junctions.

Of the four people in the study, two showed surges of gamma brainwaves in their TPO junctions when their life support was withdrawn. This surge lasted a few minutes and was very intense at times, says Borjigin, but it is impossible to know if these people had any visions as they were dying. “Had they survived, those two patients might have had some story to tell, “says Borjigin.

The other two people didn’t show any gamma brainwaves. The brains of the two who did exhibit a wave of activity were working enough to raise their heart rate as their blood oxygen levels fell. This suggests that a functioning autonomic nervous system may be necessary for the gamma brainwave surge to occur (PNAS, doi.org/gr6x8d).

These two people also had a suspected history of epilepsy, which could have permanently affected their brains. But it hasn’t previously been noted that epilepsy is linked to having a near-death experience, says Borjigin.

Sam Parnia at NYU Langone Health says a gamma wave surge could happen as people die because falling oxygen levels disable some natural “braking systems” on brain activity. “This allows for the activation of normally dormant pathways, which are seen as transient electrical spikes,” he says. “The braking systems that require energy are lost.”

The findings provide additional evidence for awareness in some people who are otherwise thought to be unconscious at the end of their life, says Parnia.

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