Scientists have been studying what happens to people in the moments before death, and their findings have raised some surprising questions about whether a person can still hear what is happening around them after their heart has stopped beating.
For many years, people have believed that dying might involve seeing a bright light at the end of a tunnel or feeling a sense of peace as they slowly lose consciousness. This idea has appeared in films, books and personal stories from people who have survived near-death experiences.
However, researchers say the reality may be very different. Some people who suffered cardiac arrest and were later brought back to life have described experiences that are far more disturbing than simply seeing a bright light.
One of the most unsettling claims comes from patients who say they could hear doctors and nurses talking about their condition, even when medical staff believed they were unconscious.
Some have even reported hearing medical professionals announce that they had died.
This has led scientists to investigate whether the human brain might remain capable of some form of awareness during the early stages of cardiac arrest, when the heart stops pumping blood around the body.
When a person’s heart stops beating, blood and oxygen can no longer reach the brain normally. Without oxygen, the brain quickly begins losing its ability to function, and the person usually becomes unconscious within seconds.
However, researchers have discovered that the process of dying may be more complicated than previously understood.
Dr Sam Parnia, a specialist in critical care and resuscitation research at NYU Langone School of Medicine in New York, has spent years investigating what people experience when their hearts stop and doctors attempt to bring them back to life.
He and his research team have examined the experiences of cardiac arrest survivors who were successfully resuscitated after their hearts stopped beating.
During these investigations, some patients described unusual memories from the time they were receiving emergency treatment.
Several said they remembered hearing conversations between medical workers. Others reported seeing what was happening around them, despite appearing unconscious during the emergency.
In some cases, patients gave descriptions of events that medical staff said were consistent with what happened during their treatment.
These accounts have attracted considerable attention because they raise questions about how much awareness a person might have while their body is undergoing a life-threatening medical emergency.
One particularly disturbing possibility is that a patient could hear doctors discussing their condition or attempting to save their life while being completely unable to respond.
Imagine lying in a hospital bed, unable to move, open your eyes or speak, while hearing people around you discussing whether you will survive.
For someone experiencing such a situation, it could be extremely frightening.
However, scientists have warned that these accounts do not prove that people remain conscious after irreversible death. The patients involved survived cardiac arrest, and researchers are still trying to establish exactly when their reported experiences occurred.
Dr Parnia explained that doctors traditionally record the time of death based on when the heart stops beating.
He said that once the heart stops, blood circulation to the brain is interrupted, causing normal brain function to fail rapidly.
Important reflexes controlled by the brainstem, including responses involving the pupils and throat, can also disappear.
But cardiac arrest is not always the same as irreversible death. With successful resuscitation, circulation can sometimes be restored, allowing the patient to survive.
This distinction is important because researchers are investigating what happens during the period when the heart has stopped but emergency treatment is still taking place.
Another scientific investigation has added to the mystery.
In 2013, researchers at the University of Michigan studied electrical activity in the brains of nine anaesthetised rats after experimentally induced cardiac arrest.
They discovered a brief increase in certain patterns of brain activity shortly after the animals’ hearts stopped.
The researchers described these patterns as being consistent with a highly activated brain state.
Their findings suggested that the brain might experience a short period of unusual electrical activity during the early stages of dying.
However, because the experiment involved animals, scientists could not determine whether the rats were conscious or experiencing anything similar to the near-death experiences reported by humans.
The findings also do not establish that people can hear conversations after their brains have permanently stopped functioning.
Nevertheless, the research has encouraged further investigations into the relationship between consciousness, brain activity and cardiac arrest.
Scientists are particularly interested in understanding why some survivors remember detailed experiences while others have no memory of the event.
Some patients describe peaceful feelings, bright lights or the sensation of leaving their bodies. Others report frightening experiences, confusion or memories of medical staff trying to save them.
Researchers believe these differences could be connected to changes in brain activity, oxygen levels, medication and the way memories are formed during a medical emergency.
There is still no clear scientific explanation for every experience reported by cardiac arrest survivors.
Dr Parnia has compared his research to the way scientists investigate complicated human experiences such as love.
He explained that researchers are trying to understand the specific features of what people experience during the process of dying.
His work aims to provide a better understanding of consciousness and what happens to the brain when the body is close to death.
For doctors, this research could also have practical importance.
If some patients retain awareness during parts of resuscitation, it may help medical professionals better understand what survivors experience and how to support them afterwards.
It could also encourage greater attention to how medical workers communicate around patients who appear unconscious.
The possibility that someone might hear conversations while being unable to respond is particularly important in hospital emergency situations.
However, researchers stress that much remains unknown. Remembering a conversation after cardiac arrest does not necessarily mean the patient heard it after being pronounced dead. The memory could have formed before unconsciousness, during recovery or at another stage of treatment.
Scientists have not established that hearing continues after irreversible brain death.
Despite these unanswered questions, the findings have changed how some researchers think about the final moments of life.
What was once considered a simple and immediate loss of awareness may involve a more complicated series of changes in the brain, particularly when doctors are attempting resuscitation.
For now, one of the most striking questions remains whether a person who appears completely unconscious during cardiac arrest might still experience something happening around them.
And while science has not yet provided a complete answer, the stories shared by people who survived cardiac arrest continue to raise questions about what the human mind experiences when life is hanging in the balance.
