In a hospital, the time of death is usually recorded as the moment the heart stops beating. This usually means that the remainder of the body will no longer receive blood to keep our organs, including the brain, alive. Despite this, multiple investigations have revealed brain activity after 'death,' raising issues about when 'death' actually happens.
Brain Waves with Decapitated Rats
In 2011, van Rijn conducted research to see if decapitation caused any conscious experiences in the brains of awake and anaesthetized rats. Electrodes were affixed to the rats' heads as part of the surgery, and EEG recordings were taken 30 seconds before decapitation and for 5 minutes after decapitation.
Awake animals showed consciousness and sensory awareness prior to decapitation. There was a quick reduction in EEG signal (power to the brain) after decapitation, followed by the existence of artefacts from chewing movements a few seconds later. The EEG signal flattened out around 15 seconds after the decapitation, indicating that there was no sensory awareness, cognition, or attention.
However, between 50 and 80 seconds after decapitation and the decay of the EEG signal, all rats showed a big but sluggish wave-form on the EEG. The scientists suggest that this is the point at which neurons lose their electrical capacity and a massive inflow of ions triggers a simultaneous mass depolarization across the brain, resulting in a 'wave of death.' This wave was also discovered in another study that looked at brain waves in individuals as they died, and they noticed a massive sluggish wave near death.
This study reveals that after decapitation, all consciousness and sensory awareness is lost practically immediately (within 10 seconds); yet, neurons in these rats continue alive for up to a minute after synchronizing displaying a loss of electrical activity. This shows that physical death and brain death are separated by a significant amount of time.
EEG Recordings of Patients Withdrawing from Life Support
EEG activity was recorded in four dying patients who had their life support turned off in a study by Norton et al (published in 2017). One of the four individuals continued to have cerebral activity 10 minutes after being declared clinically dead (i.e. absence of pulse or pupillary action). This patient had brain waves that were identical to those found in deep sleep. This was in contrast to the previous study's delayed death wave, which was observed in certain persons leading up to their death.
The researchers were unable to provide a rationale why this patient displayed brain activity after death after ruling out any technical concerns that could have thrown off the reading and providing any neurological explanation for the EEG recording thus late after death.
Three of the four patients showed signs of brain activity fading a few minutes before death, which was typical. However, one of the four patients had persistent electrical activity that could not be attributed to any technical failure. This was likewise unaffected by the sluggish 'wave of death' seen in rats following decapitation or in certain people before to death. What caused this is still unknown, but it does provide insight into how people perceive the world after death. Is it possible that this patient was awake at this time, and is it possible that they were aware after they were pronounced dead?Before and after death, all four patients had distinct EEG signals in the frontal brain, indicating that death may be a one-of-a-kind event for each person.