People who have had near-death experiences often describe intense sensations—seeing a bright white light, encountering a deceased loved one, or other extraordinary occurrences. The fact that these accounts are so common and share striking similarities has raised an intriguing question: Is there a scientific explanation for them?

Up until a few years ago, scientists believed that once the heart stopped pumping blood, the brain became inactive, as people no longer responded to their names or other stimuli.

However, in a study published in the journal of the U.S. National Academy of Sciences, neurologist Jimo Borjigin from the University of Michigan described how nearly a decade ago, she and her team were conducting experiments on rats to observe their neurochemical reactions after surgery. To their surprise, when two rats died, one of them showed a massive surge in serotonin.

This unexpected finding led Borjigin and her team to repeat the experiment. They observed that in several rats, after their hearts stopped beating and their brains were deprived of oxygen, there was a sudden spike in neurotransmitter activity—particularly serotonin and dopamine, which induce feelings of well-being, and norepinephrine, which triggers alertness.

What Happens in the Human Brain at the Moment of Death? The Role of Neurotransmitters

The brain is one of the most complex organs in the human body, weighing about 1.5 kg (roughly 3.3 lbs). In an average-sized person, this accounts for just 2% of their body weight. Yet, it is incredibly demanding, requiring a constant supply of nutrients and consuming 20% of the body’s total energy, explains Luis B. Tovar y Romo, director of the Institute of Cellular Physiology at the National Autonomous University of Mexico (UNAM).

For proper function, the brain relies on a continuous supply of oxygen and glucose delivered by the bloodstream. These elements allow neurons to generate ATP (adenosine triphosphate), the molecule that serves as the primary energy source for cellular functions in all living organisms. Without ATP, fundamental processes like muscle contraction, digestion, glandular secretion, and blood circulation would be impossible.

In particular, ATP is essential for maintaining the membrane potential that enables communication between billions of neurons. This neural communication generates small electrical impulses, which can be recorded as brain waves.

Brain waves come in different frequencies—some fast, others slow—and can be observed using an electroencephalogram (EEG). When a person dies, blood flow to the brain ceases, cutting off its oxygen and glucose supply, leading to failure.

Yet, even as this shutdown occurs, certain neuronal functions persist. Neurons can still respond to neurotransmitters like serotonin, dopamine, and glutamate, generating electrical activity for a brief period. Scientists have confirmed this by recording EEG activity in some patients at the moment of death.

This means that even after a person is declared dead, and there is no longer a state of consciousness, the brain remains active because some neurons are still alive—though they rapidly deteriorate, Tovar explains.

People who experience cardiac arrest and are revived often display unusual neural activity due to the massive release of neurotransmitters. When circulation is restored, they frequently recall seeing lights or having other vivid sensations.

This phenomenon is tied to the brain’s highly active circuits, which never fully shut down. For instance, when we dream, the experiences feel real—we don’t realize we’re dreaming.

Something similar may happen to those who come close to death. The sensations they recall might be a different kind of dream, triggered by disrupted neural mechanisms due to a lack of energy.

For a few minutes, the brain continues to function, and these circuits remain active, but they eventually shut down as energy depletes. It’s similar to a car running on fumes—it can keep moving for a short distance before coming to a complete stop.

“If you refuel the car just in time, it starts up again, though it might not function perfectly at first. This is comparable to reviving a person after a near-death experience,” Tovar explains.

Gamma Waves: A Last Burst of Brain Activity

Building on her previous work, neurologist Jimo Borjigin recently conducted a new study involving four comatose patients on life support, all connected to EEG monitors.

When doctors and families determined that further treatment was futile, life support was withdrawn. In two of the patients, this led to a sudden spike in heart rate, accompanied by an increase in gamma wave activity.

Gamma waves are associated with memory retrieval and information processing. They are particularly active during dreaming, meditation, and intense concentration.

Borjigin theorizes that as these oscillations emerge, the brain may be replaying significant life events—a final memory flashback similar to what near-death survivors describe.

However, given that the study involved only two individuals, Borjigin acknowledges that much more research is needed before drawing definitive conclusions. Furthermore, since both patients passed away, it’s impossible to determine what they actually experienced.

Still, she believes these findings are just the tip of the iceberg, hinting at a vast, unexplored territory in the study of consciousness and death. (CIENCIA UNAM)

This article is being republished as part of a collaboration between UNAM and Tec to promote science outreach.