Seeing a white light, encountering an otherworldly presence, and watching one’s life flash before one’s eyes are all well-worn cliches associated with dying, yet research shows that these phenomena are in fact surprisingly common during near-death experiences (NDEs). Reported by people from all countries and cultural backgrounds, these ethereal motifs arise time and again when death is near, raising question marks as to whether they arise from a material source.

Naturally, the material in question here is neural tissue, and scientists have spent years trying to determine if NDEs can be explained by brain activity. As a starting point, studies have revealed that strokes, seizures, and brain injuries can lead to abnormal functioning within the medial temporal area and the temporoparietal junction, resulting in psychological experiences that resemble NDEs. Some seizures can also trigger altered activity within the anterior insular cortex, which occasionally generates intense feelings of ecstasy and other phenomena associated with dying.

Furthermore, changes in brainwave oscillations have been observed in rats having heart attacks, implying that brain activity may radically alter as we bow out from the physical realm. Yet while all of these findings hint at a neurological explanation for NDEs, the riddle surrounding these fantastic encounters has yet to be solved.

What we do know, however, is that around one in ten people claim to have undergone some sort of NDE, whether during a cardiac arrest, childbirth, or after being struck by lightning. Such experiences can be identified using a tool called the Greyson Near-Death Experience Scale, which quantifies the various aspects of these experiences, including an altered perception of time, heightened senses, and a feeling of separation from one’s physical body.

Interestingly, many of these phenomena are associated with rapid eye movement (REM) sleep, when the brain is highly active and vivid dreams occur. Other aspects of NDEs, meanwhile, strongly resemble the effects of certain psychoactive drugs. After reading written reports of thousands of NDEs and drug-induced experiences, a team of researchers concluded that ketamine is the substance that most consistently generates NDE-like hallucinations, and often produces a sense of leaving one’s body.

Intriguingly, ketamine’s ability to block NMDA receptors in the brain has been linked to reductions in damage following strokes. This has led some scientists to speculate that certain similar chemicals may be released by the brain at the moment of death in an attempt to protect itself and keep neurons alive as oxygen levels drop.

Though unproven, a similar theory states that the psychedelic compound DMT could perform the same function, and some researchers have speculated that the brain may secrete this trippy molecule when we die. Interestingly, a recent study found that the experience produced by DMT is often strikingly similar to an NDE.

Whether or not these hypotheses turn out to be true, they do strengthen the argument that, like drug-induced experiences, NDEs are probably caused by changes in brain activity rather than direct contact with a supernatural dimension.

One scientist who is determined to prove that this is the case is Dr Steven Laureys, a neurologist at the Centre Hospitalier Universitaire de Liège in Belgium. In a recent documentary, Dr Laureys demonstrated how the brain generates many of the phenomena associated with NDEs, providing plausible explanations for these bizarre experiences.

For instance, he revealed how reduced blood flow to the brain causes peripheral vision to shut down, resulting in a kind of tunnel vision that resembles the experience of traveling down a dark corridor towards a bright light. He also showed how the brain searches its own memory bank in order to generate familiar sounds and visions when faced with a lack of stimuli, potentially explaining why people see their life flash before them or hear voices when they are close to death.

In spite of these advancements, however, we still can’t say for sure why people undergo these classic experiences, and while it’s likely that responsibility lies with the brain, there’s always a chance that it’s actually ghosts or something.