Nine rats were implanted with electrodes in various brain regions, anaesthetised then 'euthanized' (i.e., killed). The exact moment of death was identified as the last regular heartbeat (clinical death). Electroencephalogram (EEG) was recorded during normal waking phase, anaesthesia and after cardiac arrest (i.e., after death) from right and left frontal (RF/LF), parietal (RP/LP) and occipital (RO/LO) cortex. The raw EEG (i.e., ‘brain waves') for each area is shown in the Figure below. On top (Panel A), the recording ranges from about 1hr before death to 30mins afterwards. At this coarse time scale you can basically see a sudden decrease in brain activity after cardiac arrest - everything seems to flatline at the moment of death. However, if we now zoom in on the moment just after death (Panels B and C below), we can see that the death process actually involves a sequence of structured stages, including a surge of high-frequency brain activity that is normally associated with wakefulness and conscious awareness.
In this study, the neuroscientists distinguish four distinct stages of brain death. Cardiac arrest stage 1 (CAS1) reflects the time (~4 seconds) between the last regular heartbeat and the loss of a oxygenated blood pulse (i.e. clinical death). The next stage (CAS2) lasts about 6 seconds, and ends with a burst in low-frequency brain waves (so-called 'delta blip'). The third death stage, CAS3, lasts approximately 20 seconds at which point there is no more evidence of meaningful brain activity at the final stage, CAS4.
In 2013 as the real big cause of "near-death experiences." It seems that, just after we die, a gigantic spike happens in brain activity. It's very, very brief, and it's only been observed in rats (because tests performed on dying humans are obviously hard to get past the ethics committee). But it's the sort of brain activity we'd expect to see in conscious, thinking humans — humans who are not just awake, but alert and contemplating something. Essentially, you may "wake up" extremely briefly after death — using a large amount of the neural connections depicted in the image above, which was generated by researchers at Brown University to depict the ways our brains function.
The study, from the University of Michigan, has been characterized as explaining why people who have had serious heart-related difficulties — the kind where blood flow to the brain ceases entirely— seem to experience moments of incredibly clear perception after the point where their brains should have ceased functioning. The cause may not be entirely clear, but it's somewhat comforting to think that our brains may give us one last, very real sense of experience before we go.
Within the first 30 seconds after cardiac arrest, all of the rats displayed a widespread, transient surge of highly synchronized brain activity that had features associated with a highly aroused brain.
Furthermore, the authors observed nearly identical patterns in the dying brains of rats undergoing asphyxiation.
“The prediction that we would find some signs of conscious activity in the brain during cardiac arrest was confirmed with the data,” says Borjigin, who conceived the idea for the project in 2007
“But, we were surprised by the high levels of activity,” “ In fact, at near-death, many known electrical signatures of consciousness exceeded levels found in the waking state, suggesting that the brain is capable of well-organized electrical activity during the early stage of clinical death.”
The brain is assumed to be inactive during cardiac arrest. However the neurophysiological state of the brain immediately following cardiac arrest had not been systemically investigated until now.
“This study tells us that reduction of oxygen or both oxygen and glucose during cardiac arrest can stimulate brain activity that is characteristic of conscious processing,” says Borjigin. “It also provides the first scientific framework for the near-death experiences reported by many cardiac arrest survivors.”
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