We often think of death as an on-off switch. One minute youre there, and the next its lights out.
Not so. During heart failureone of the largest medical killers globallythe brain gradually loses access to oxygen in the blood, but sparks of activity linger. Far from the last gasp of the brains descent into permanent unconsciousness, scientists have long thought these electrical signals may explain near-death experiences, and more broadly, consciousness.
Reports of near-death experiences span various ages, cultures, and ethnicities. The luckily revived few often describe vivid visions of tunnels of white light, floating outside their own bodies, or reconnecting with departed loved ones.
To Dr. Jimo Borjigin at the University of Michigan School of Medicine, Ann Arbor, these realer-than-real shared experiences suggest a common, if paradoxical, theme: rather than having its electrical lights flipped off, dying actually triggers a surge of activity in the human brain.
A new study led by Borjigin hints at the first proof of concept of the radical idea. As four comatose patients were sustained by life support, her team detected a surge of brain activity in two of them following withdrawal as they passed on.
The neural activity patterns are far from random. The dying brain generated waves of gamma band activity, a fast oscillating electrical wave thats often associated with conscious processing and thoughts. The team detected these signals both within a critical hot zone and other brain regions previously linked to consciousness.
To be clear, its highly unlikely the comatose participants regained consciousness right before death. Rather, the study shows that the dying brain generates a swan songone that may explain lucid visions and out-of-body experiences as they occur in the mind.
How vivid experience can emerge from a dysfunctional brain during the process of dying is a neuroscientific paradox. Dr. Borjigin has led an important study that helps shed light on the underlying neurophysiological mechanisms, said study author Dr. George Mashour, the founding director of the Michigan Center for Consciousness Science.
Consciousness comes in two flavors.
One is overt: the person is alert and can easily interact with the outside world. The more mysterious half is covert. Here, the person may be conscious in the sense that they are aware of themselves and their surroundings, but unable to show it. This often happens in people with brain injuries such as trauma, stroke, or locked-in syndrome. Back in 2006, a study measuring brain activity using fMRI from a young woman who appeared vegetative surprisingly found that her brain responded to different cognitive tasks even though her body couldnt. Subsequent studies used EEG (electroencephalography) to probe for signs of consciousness in unresponsive peopleincluding the comatose and the dying.
Borjigin is no stranger to studying the dying brain. Back in 2013, her team ran a seminal trial in nine rats, measuring their brain waves as heart failure took over. Previous attempts at hunting down the neurobiological underpinnings of near-death experiences and consciousness during the dying process had mostly focused on individual neurochemicals, such as dopamine and glutamate. Few had examined brain activity directly on a global scale.
In that study, the team fitted rats with electrodes to measure their brain wavesneural oscillations of electrical activity. Like ocean waves, these come in different frequencies similar to radio channels. Each loosely captures a certain mental state. Alpha waves, for example, occur frequently during relaxed wakefulness. Beta waves are linked to cognitive processing while alert.
But gamma waves caught Borjigins attention. These neural oscillations were initially recorded in monkeys as a measure of visual perception, even when some questioned their existence. The mysterious waves subsequently gained traction as they appeared during REM sleepthe stage of sleep often associated with vivid dreams and visualsand even a feeling of bliss after meditation.
After chemically inducing cardiac arrest in the rats, the team found that most brain wave frequencies tanked in strength (known as power). Surprisingly, gamma bands spiked in power and became more synchronizeda marker often associated with a highly conscious alert statebut didnt necessarily prove they were alert or awake.
Rats are obviously not humans. Flash forward to 2022, a separate team captured an 87-year-old mans brain activity when he unexpectedly died. Similarly, his brain burst with gamma wave activity for 30 seconds as his heart stopped.
The new study embraced a precious data resource: EEG recordings from four comatose patients with little chance of recovery following cardiac arrest. None of the people showed any signs of overt consciousness and relied on machine ventilation. In 2014, their loved ones agreed it was time for them to pass on. Each person was fitted with an EEG cap to measure their neural activity as they were removed from their ventilators.
For 30 seconds to 2 minutes, two patients brains surged with gamma waves. The activity was both localized within a brain regionthe temporo-parietal-occipital junction, or TPOand also spread out to the front part of the other brain hemisphere.
Often considered a neural key gateway for processing visual environments, the TPO could be a hot zone for how the brain generates consciousness, the team explained. Similar to previous animal experiments, the patients gamma waves better synchronized in these hot zones and across brain regions.
These data demonstrate that the human brain can be active during cardiac arrest, said the team.
The results are similar to the 2022 octogenarian study. But the subject pool remains small, and as scientists transition from rodent to human studies, consistency is key.
The more consistent findings we have, the more evidence it is that this likely is a mechanism happening at the time of death and if we can pinpoint this down to one location, even better, said Dr. Ajmal Zemmar, a neurosurgeon at the University of Louisville Health who was not involved in the current work but co-authored the 2022 study.
Others are less convinced. To Dr. Daniel Kondziella at the University of Copenhagen, who was not involved in the study, the results arent surprising. Because dying from cardiac arrest takes time, its likely that neural activity goes haywire in the minutes between the heart stopping and brain death.
To Borjigin, the study is just beginning to explore brain activity at the end of life. Particularly interesting is that the two people with a gamma wave surge both had limited bouts of epilepsy. Although epilepsy is a disorder marked by aberrant neural activity, neither experienced seizures within the 24 hours prior to the study.
While unlikely, its possible that the EEG electrodes placed on the patients scalps didnt capture deeper seizures that triggered the gamma activity. Its something to further investigate, the authors said. Similarly, the study wasnt able to correlate the brain activity to the patients personal experiences as they passed.
In other words, we dont yet know if these waves support or generate near-death experiences. However, the observed findings are definitely exciting and provide a new framework for our understanding of covert consciousness in the dying humans, said Borjigin.
For now, the team is looking to expand the study beyond four people to better hunt down signs of gamma waves in the dying brain. But more importantly, the work lays the foundation for further investigation of covert consciousness during cardiac arrest, and in turn, serves as a model system to explore mechanisms of human consciousness, they said.
Image Credit: Gerd Altmann / Pixabay
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