Death is usually identified by the ceasing of the heartbeat; blood can no longer be circulated to the various parts of the body where it is needed, and without oxygen the major processes of life begin to falter before eventually stopping entirely. Despite this, evidence suggests that our brains continue to operate normally for up to 10 minutes after everything else has withered away.
After the heart stops beating, consciousness remains for about 20 seconds due to the fact that the cerebral cortex (the part of the brain responsible for thinking and decision making) does not require oxygen to survive. Just as the loss of oxygen begins to affect the brain itself, it receives an inexplicable surge of electricity. Brain cells then begin to release chemical pathways leading to cell apoptosis (cellular death) of the organ. But since one is still technically conscious while all this is occurring, this begs the question of how people’s brains process this and how a person perceives it; what do you see as you are dying?
Researchers at the University of Michigan found that, in rat test subjects, neurophysiological activity in the near-death state exceeded levels in the conscious, waking state. Brain activity shortly after clinical death similarly displayed patterns characteristic of conscious perception. It seems the mammalian brain can inexplicably generate heightened neurological activity when close to death and this can, according to Michigan Medical School, form the basis for future investigations into mental experiences during that state. This includes ‘seeing light’ and other ‘realer than real’ experiences during cardiac arrest, of which 20% of survivors report to have had.
Another phenomenon associated with near-death experiences is the so-called ‘life review experience’ (LRE); when a person’s life “flashes before their eyes”. Those who have had LRE commonly report losing all sense of time with memories hitting them from any point in their entire lives. Another universal feature was extremely emotional experiences often seen through the eyes of another individual, usually someone significant in a person’s life. This event, which usually leaves the survivor with a new perspective on their life events and of other people close to them, have been linked to the areas of the brain responsible for the storage of autobiographical memories. The memory centre survives for longer than all the other regions of the brain; like the cerebral cortex it is not affected by blood loss but by the eventual the death of the rest of the organ around it becoming too significant. It is possible that, as these parts of the brain slowly succumb to the lack of oxygen, they release their stored memories as a non-linear representation of one’s life. Previous research into this phenomenon has found that it is more common in people with raised levels of carbon dioxide in their blood and breath following cardiac arrest.
It is clear that our perception of being ‘dead’ is not as black and white as we may think at face value. Long thought to be a convenient plot twister reserved for those working at Hollywood, it seems that phenomena like life reviews actually do have a basis in science. It also raises the question of whether our definition of death needs to change; is it ethical to pronounce someone as dead when one of the most vital areas of their body is still indeed operating normally and arguably continuing to generate some form of conscious thought?