When Your Brain Stops But You Don’t: The Near-Death Experience Puzzle

Bruce Greyson sees patients flatline and come back different. Some return with stories that shouldn’t exist: vivid memories from moments when their brains showed no activity, detailed accounts of conversations in distant rooms, encounters with deceased relatives whose deaths they couldn’t have known about. For nearly five decades at the University of Virginia, he’s collected these accounts, and the more he gathers, the less the brain-based explanations seem to fit.

A multinational team recently attempted to solve this puzzle with an ambitious model called NEPTUNE. Neurophysiological Evolutionary Psychological Theory Understanding Near-Death Experience. It was meant to be comprehensive, pulling together decades of hypotheses about blood gases, brain chemicals, and electrical surges into one coherent framework.

But Greyson and his colleague Marieta Pehlivanova aren’t convinced. In a new paper, they’ve dismantled NEPTUNE piece by piece, revealing a pattern that’s plagued near-death research for years: elegant theories that explain some features whilst ignoring the most perplexing ones. The NEPTUNE team suggested that oxygen deprivation might trigger hallucinations, that stimulating a brain region called the temporoparietal junction could produce out-of-body sensations, that a neurochemical called ketamine might replicate the tunnel of light. Yet none of these explanations account for what makes near-death experiences so fundamentally strange—not the sensations themselves, but their apparent accuracy.

Consider the hallucination hypothesis, which NEPTUNE relies on heavily. Neurological hallucinations typically involve a single sense, hearing voices or seeing phantom shapes, and they’re accompanied by confusion and fear.

Near-death experiencers describe something entirely different: multisensory encounters with deceased loved ones that feel “more real than real,” conversations that convey specific information, perceptions that persist in memory for decades with crystalline clarity. Some meet relatives they’ve never encountered, only to later discover details about those people’s deaths that they couldn’t possibly have known. That’s not how hallucinations behave.

The out-of-body problem gets even thornier. NEPTUNE points to studies where electrical stimulation of the temporoparietal junction produced what researchers labelled as out-of-body experiences, but the patients themselves never used that term.

What they actually reported was feeling their body tilt or sensing a shadowy presence behind them, all whilst their visual perception remained anchored to their physical eyes. During genuine near-death out-of-body experiences, people describe floating above their bodies, watching resuscitation efforts from the ceiling, seeing events in distant rooms, and crucially, some of these perceptions have been independently verified. A cardiac surgeon once reported details of his own emergency surgery that he witnessed from outside his body, observations his assistant later confirmed. Electrical brain stimulation has never produced anything resembling that level of specific, accurate, external perception. There’s a rather large difference between feeling tilted and accurately describing the pattern on a nurse’s shoes from a vantage point you shouldn’t have.

Then there’s the timing puzzle that NEPTUNE tried to sidestep. The model suggests these experiences might occur before cardiac arrest or during brief moments of partial brain activity.

But some cases include what researchers call “time anchors”. Verified perceptions that could only have occurred during complete loss of consciousness. Greyson points to patients who accurately described specific resuscitation details, conversations between medical staff, or equipment brought into the room, all during periods when EEG readings showed no brain activity capable of forming memories.

The NEPTUNE team made a philosophical choice that Greyson finds telling: they excluded all non-physicalist theories from consideration, citing a “fundamental tenet of neuroscience” that all human experience arises from the brain. Yet one of their own cited sources (neuroscientist Giulio Tononi) has since disavowed that very tenet, writing that consciousness remains “unexplained, not to say magical” in purely computational terms.

Science, Tononi argued, won’t benefit from a tribunal deciding which approaches are permissible. Perhaps the most revealing gap in NEPTUNE appears in its treatment of recent studies claiming to show electrical “surges” in dying brains, evidence that vivid experiences might occur in the final moments.

Greyson examined those studies carefully. In every case, the patients’ hearts were still beating during the electrical activity. None regained consciousness to report any experiences. None showed behavioural signs of awareness. The electrical patterns detected were also typical of muscle spasms in the scalp. A well-known contamination source in EEG readings. Most damningly, one large study that did collect reports found zero overlap between patients who showed the purported consciousness-associated brain activity and patients who actually reported near-death experiences.

Greyson and Pehlivanova aren’t dismissing physiology, near-death experiences clearly have physiological triggers. But they reckon the current evidence shows these triggers aren’t sufficient explanations, particularly for the veridical perceptions that keep appearing in the data. As Greyson puts it, we’re still at the beginning stage of understanding these experiences, and the quest shouldn’t just map their triggers but explore their meaning and what they reveal about the boundaries between consciousness and brain activity. The door to that mystery, it seems, remains stubbornly open.