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 past memories and hearing or seeing deceased relatives have all been reported by people from many cultures who have had a brush with death. Sceptics, however, say these experiences could be caused by people hallucinating as they recover in hospital.
Now, it seems we may have identified the brain activity 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.
Some people who are critically ill in intensive care units have electrodes placed on their head to monitor their brainwaves in a technique called electroencephalography, or EEG, if doctors think they are at risk of having epileptic seizures.
Borjigin’s team combed through anonymised medical records for people who had an EEG recorded as their life support was switched off because they had no hope of recovery, finding four such people.
Brainwaves can be seen on an EEG when large numbers of brain cells fire together in synchronised 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 temporo-parieto-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the four people in the study, two showed surges of gamma brainwaves in their TPO junctions when their life support was withdrawn.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 in brainwaves lasted a few minutes and was very intense at times, says Borjigin. “It was crazy high.”
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.
Unlike the other two individuals, who didn’t show any gamma brainwaves, the two that did had brains that were still 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.
These two people also had a suspected history of an epileptic seizure, which could have permanently affected their brains. But it hasn’t previously been noted that people with a history of epilepsy are more likely to have a near-death experience, says Borjigin.
Sam Parnia at NYU Langone Health says the gamma wave surge might 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 supporting evidence for awareness in some people who are otherwise thought to be unconscious at the end of their life, says Parnia.