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People who have stood at the edge of life often return with stories that defy scientific logic: vivid recollections, out-of-body visions, and overwhelming emotional clarity.
A new analysis led by Dr. Bruce Greyson and Dr. Marieta Pehlivanova at the University of Virginia School of Medicine challenges a major neuroscience framework known as NEPTUNE. The researchers argue that while this model attempts to explain NDEs through brain chemistry, oxygen levels, and evolutionary psychology, it leaves out critical scientific evidence and fails to account for the most defining aspects of these experiences.
Often described as more real than everyday life, near-death experiences can involve sensations of peace, the perception of leaving the body, movement through tunnels, or encounters with deceased relatives. Many people remember these events with sharp clarity, even decades later. The new study, published in Psychology of Consciousness: Theory, Research and Practice, examines why no current model, including NEPTUNE, has succeeded in explaining the phenomenon.
Oxygen and Carbon Dioxide Levels Don’t Match Near-Death Reports
The NEPTUNE model, short for Neurophysiological Evolutionary Psychological Theory Understanding Near-Death Experience, suggests that chemical and physical changes in the brain may trigger NDEs. It points specifically to fluctuations in oxygen or carbon dioxide levels, as well as changes in neurotransmitters, as potential causes.
But according to Dr. Greyson and Dr. Pehlivanova, scientific data contradicts these assumptions. Many people who report NDEs show normal or even elevated oxygen levels during the events. While shifts in carbon dioxide may help explain why certain memories become more accessible, they do not clarify how the experience begins in the first place.
“The NEPTUNE model was a pioneering attempt to explain NDEs,” said Dr. Greyson, “but it selectively ignored scientific evidence that contradicts the model and failed to address some of the most important and defining parts of NDEs.” That evidence includes cases where brain chemistry does not align with the intensity or clarity of the experiences described.
Sensory Depth and Emotional Impact Rule Out Hallucination
NEPTUNE often describes NDEs as hallucinations produced by neurological stress. But medical hallucinations usually involve only one sensory modality, such as visual or auditory disturbances. In contrast, NDEs frequently engage multiple senses simultaneously, including sight, sound, touch, and deep emotion.
These experiences also tend to have a lasting emotional and psychological impact, unlike typical hallucinations, which fade quickly. People who experience NDEs often report a stronger sense of compassion, a new purpose in life, and a significant reduction in the fear of death, long-term changes not commonly seen in hallucination cases.
Some near-death episodes include out-of-body experiences, during which people say they observed events around them from a position outside their physical body. NEPTUNE attributes this to activity in the temporoparietal junction of the brain. However, studies involving electrical stimulation of this region fail to produce convincing matches.
Laboratory subjects may experience strange sensations or spatial confusion, but they do not believe their consciousness has actually left their body, and their vision and mobility remain normal. As the researchers wrote, “There is no evidence that electrical brain stimulation has ever produced accurate perception of anything not visible to the physical eyes, or that persists when eyes are closed, or that is from an out-of-body perspective—all features observed in spontaneous OBEs,” reports Earth.com.
The study adds that epileptic seizures, which also affect the temporoparietal junction, do not generally lead to NDE-like experiences, further weakening this line of explanation.
Comparisons to Drugs Reveal Major Differences
NEPTUNE also draws comparisons between NDEs and the effects of psychedelic drugs like ketamine or DMT. While both types of experiences may involve sensations of detachment from the body, Dr. Greyson and Dr. Pehlivanova argue that the differences are more significant than the similarities.
Drug-induced states often feel fragmented, are emotionally shallow, and fade quickly. In contrast, NDEs are typically described as deeply meaningful, highly coherent, and permanently memorable. Even Karl Jansen, a prominent ketamine researcher, later stated that ketamine does not actually produce near-death experiences, but may give access to related mental states.
Some recent studies have noted brief electrical surges in the brain near the time of death, which NEPTUNE points to as potential triggers for conscious awareness. But many of the patients in those studies still had active heart rhythms, and showed no clinical signs of awareness. In cardiac arrest research, the observed electrical patterns also failed to match the characteristics reported in actual near-death experiences.
The study stresses that the timing and quality of these surges don’t correlate with the rich experiences people recall. Most significantly, some NDEs include accurate observations of external events that occurred while the person was fully unconscious and lacked measurable brain activity—details that NEPTUNE does not explain.
According to the researchers, such cases highlight the limitations of current models that rely solely on internal brain function. “NDEs are typically triggered by physiological events,” said Dr. Greyson, “so it makes sense to explore those connections and look for cause-and-effect… but this effort is just at the beginning stage, and it is important to keep being open-minded as we continue the search.”
