Morse's 1994 report, commonly referred to as the Seattle study and published in Current Problems in Pediatrics, spanned a decade. During that period, he interviewed 160 children in the intensive care unit at Children's Hospital in Seattle who had been revived from apparent death. Every one of these children had been without a pulse or sign of breathing longer than 30 seconds. Some had been in that state for as long as 45 minutes; the average apparent death lasted between 10 and 15 minutes. For a control group, he used hundreds of other children also in intensive care, also on the brink of death, but whose pulse and breathing hadn't been interrupted for more than 30 seconds. That was the only difference. In other dimensions—age, sex, drugs administered, diseases suffered, and setting—the groups were the same. In setting, Morse not only included the intensive care unit itself but also scary procedures such as insertion of a breathing tube and mechanical ventilation. These are important additions because fear has long been considered a trigger for a near-death experience (and might have been the trigger responsible for what happened when I skydived).

Morse graded his subjects' experiences according to the Greyson scale, a 16-point questionnaire designed by University of Virginia psychiatrist Bruce Greyson that remains the benchmark for determining whether or not an anomalous experience should be considered a near-death experience. Using this test, Morse found that 23 out of 26 children who experienced apparent death—the cessation of heartbeat and breathing—reported a classic near-death experience, while none of the other 131 children in his control group reported anything of the kind.

Morse later videotaped the children recalling their experiences, which included such standard fare as long tunnels, giant rainbows, dead relatives, and deities of all sorts. But many descriptions—augmented by crayon drawings—included memories of the medical procedures performed and details about doctors and nurses whose only contact with the child occurred while the child was apparently dead.

Other scientists have duplicated Morse's findings. Most recently, cardiologist Pim van Lommel, a researcher at Rijnstate Hospital in Arnhem, the Netherlands, conducted an eight-year study involving 344 cardiac-arrest patients who seemed to have died and were later revived. Out of that total, 282 had no memories, while 62 reported a classic near-death experience. Just as in Morse's study, van Lommel examined the patients' records for any factors traditionally used to explain near-death experiences—such as setting, drugs, or illness—and found no evidence of their influence. Apparent death was the only factor linked to near-death experiences. He also found that one person in his study had difficult-to-explain memories of events that happened in the hospital while he was presumed dead.

Possible clues to the biological basis of these unusual states turned up in studies conducted in the late 1970s, when the Navy and the Air Force introduced a new generation of high-performance fighter planes that underwent extreme acceleration. Those speeds generated tremendous g-forces, which pulled too much blood out of the pilots' brains, causing them to black out. The problem, known as G-LOC, for g-force-induced loss of consciousness, was serious, and James Whinnery, a specialist in aerospace medicine, was in charge of solving it.

Over a 16-year period, working with a massive centrifuge at the Naval Air Warfare Center in Warminster, Pennsylvania, Whinnery spun fighter pilots into G-LOC. He wanted to determine at what force tunnel vision occurred. More than 500 pilots accidentally blacked out during the study, and from them Whinnery learned how long it took pilots to lose consciousness under acceleration and how long they remained unconscious after the acceleration ceased. By studying this subset he also learned how long they could be unconscious before brain damage started.

He found that G-LOC could be induced in 5.67 seconds, that the average blackout lasted 12 to 24 seconds, and that at least 40 of the pilots reported some sort of out-of-body experience while they were unconscious. Not knowing anything about out-of-body experiences, Whinnery called these episodes dreamlets, kept detailed records of their contents, and began examining the literature on anomalous unconscious experiences. "I was reading about sudden-death episodes in cardiology," Whinnery says, "and it led me right into near-death experiences. I realized that a smaller percentage of my pilots' dreamlets, about 10 to 15 percent, were much closer in content to a classic NDE."

When Whinnery reviewed his data, he noted a correlation: The longer his pilots were knocked out, the closer they got to brain death. And the closer they got to brain death, the more likely it was that an out-of-body experience would turn into a near-death experience. This was the first hard evidence for what had been long suspected—that the two states are not two divergent phenomena, but two points on a continuum.

Whinnery found that G-LOC, when gradually induced, produced tunnel vision. "The progression went first to grayout (loss of peripheral vision) and then to blackout," he explains, and the blindness occurred just before a person went unconscious. "This makes a lot of sense. We know that the occipital lobe (the portion of the brain that controls vision) is a well-protected structure. Perhaps it continued to function when signals from the eyes were failing due to compromised blood flow. The transition from grayout to unconsciousness resembles floating peacefully within a dark tunnel, which is much like some of the defining characteristics of a near-death experience. The pilots also recalled a feeling of peace and serenity as they regained consciousness.

The simplest conclusion to draw from these studies is that, give or take some inexplicable memories, these phenomena are simply normal physical processes that occur during unusual circumstances. After all, once scientists set aside the traditional diagnosis of delusion as a source of these unusual mental states and began looking for biological correlates, there were plenty of possibilities. Compression of the optic nerve could produce tunnel vision; neurochemicals such as serotonin, endorphins, and enkephalins could help explain the euphoria; and psychotropics like LSD and mescaline often produce vibrant hallucinations of past events. But no one has directly tested these hypotheses.

What researchers have studied is the effect of a near-death experience. Van Lommel conducted lengthy interviews and administered a battery of standard psychological tests to his study group of cardiac-arrest patients. The subset that had had a near-death experience reported more self-awareness, more social awareness, and more religious feelings than the others.

Van Lommel then repeated this process after a two-year interval and found the group with near-death experience still had complete memories of the event, while others' recollections were strikingly less vivid. He found that the near-death experience group also had an increased belief in an afterlife and a decreased fear of death compared with the others. After eight years he again repeated the whole process and found those two-year effects significantly more pronounced. The near-death experience group was much more empathetic, emotionally vulnerable, and often showed evidence of increased intuitive awareness. They still showed no fear of death and held a strong belief in an afterlife.

Morse, too, did follow-up studies long after his original research. He also did a separate study involving elderly people who had a near-death experience in early childhood. "The results were the same for both groups," says Morse. "Nearly all of the people who had had a near-death experience—no matter if it was 10 years ago or 50—were still absolutely convinced their lives had meaning and that there was a universal, unifying thread of love which provided that meaning. Matched against a control group, they scored much higher on life-attitude tests, significantly lower on fear-of-death tests, gave more money to charity, and took fewer medications. There's no other way to look at the data. These people were just transformed by the experience."

Morse has gone on to write three popular books about near-death experiences and the questions they raise about the nature of consciousness. His research caught the attention of Willoughby Britton, a doctoral candidate in clinical psychology at the University of Arizona who was interested in post-traumatic stress disorder. Britton knew that most people who have a close brush with death tend to have some form of post-traumatic stress disorder, while people who get that close and have a near-death experience have none. In other words, people who have a near-death experience have an atypical response to life-threatening trauma. No one knows why.

Britton also knew about work done by legendary neurosurgeon and epilepsy expert Wilder Penfield in the 1950s. Penfield, one of the giants of modern neuroscience, discovered that stimulating the brain's right temporal lobe—located just above the ear—with a mild electric current produced out-of-body experiences, heavenly music, vivid hallucinations, and the kind of panoramic memories associated with the life review part of the near-death experience. This helped explain why right temporal lobe epilepsy was a condition long defined by its most prominent symptom: excessive religiosity characterized by an intense feeling of spirituality, mystical visions, and auditory hallucinations of the voice-of-God variety. And given what Whinnery has found, it is possible that his pilots' near-death-like dreamlets were related to brief episodes of compromised blood flow in the temporal lobe.

Britton hypothesized that people who have undergone a near-death experience might show the same altered brain firing patterns as people with temporal lobe epilepsy. The easiest way to determine if someone has temporal lobe epilepsy is to monitor the brain waves during sleep, when there is an increased likelihood of activity indicative of epilepsy. Britton recruited 23 people who had a near-death experience and 23 who had undergone neither a near-death experience nor a life-threatening traumatic event. Then, working at a sleep lab, she hooked up her subjects to electrodes that measured EEG activity all over the brain—including the temporal lobes—and recorded everything that happened while they slept.

She then asked a University of Arizona epilepsy specialist who knew nothing about the experiment to analyze the EEGs. Two features distinguished the group with near-death experience from the controls: They needed far less sleep, and they went into REM (rapid eye movement) sleep far later in the sleep cycle than normal people. "The point at which someone goes into REM sleep is a fantastic indicator of depressive tendencies," says Britton. "We've gotten very good at this kind of research. If you took 100 people and did a sleep study, we can look at the data and know, by looking at the time they entered REM, who's going to become depressed in the next year and who isn't."

Normal people enter REM at 90 minutes. Depressed people enter at 60 minutes or sooner. Britton found that the vast majority of her group with near-death experience entered REM sleep at 110 minutes. With that finding, she identified the first objective neurophysiological difference in people who have had a near-death experience.

Britton thinks near-death experience somehow rewires the brain, and she has found some support for her hypothesis regarding altered activity in the temporal lobe: Twenty-two percent of the group with near-death experience showed synchrony in the temporal lobe, the same kind of firing pattern associated with temporal lobe epilepsy. "Twenty-two percent may not sound like a lot of anything," says Britton, "but it's actually incredibly abnormal, so much so that it's beyond the realm of chance."

She also found something that didn't fit with her hypothesis. The temporal lobe synchrony wasn't happening on the right side of the brain, the site that had been linked in Penfield's studies to religious feeling in temporal lobe epilepsy. Instead she found it on the left side of the brain. That finding made some people uncomfortable because it echoed studies that pinpointed, in far more detail than Penfield achieved, the exact locations in the brain that were most active and most inactive during periods of profound religious experience.

Over the past 10 years a number of different scientists, including neurologist James Austin from the University of Colorado, neuroscientist Andrew Newberg, and the late anthropologist and psychiatrist Eugene D'Aquili from the University of Pennsylvania, have done SPECT (single photon emission computed tomography) scans of the brains of Buddhists during meditation and of Franciscan nuns during prayer. They found a marked decrease in activity in the parietal lobes, an area in the upper rear of the brain. This region helps us orient ourselves in space; it allows us to judge angles and curves and distances and to know where the self ends and the rest of the world begins. People who suffer injuries in this area have great difficulties navigating life's simplest landscapes. Sitting down on a couch, for example, becomes a task of Herculean impossibility because they are unsure where their own legs end and the sofa begins. The SPECT scans indicated that meditation temporarily blocks the processing of sensory information within both parietal lobes.

When that happens, as Newberg and D'Aquili point out in their book Why God Won't Go Away, "the brain would have no choice but to perceive that the self is endless and intimately interwoven with everyone and everything the mind senses. And this perception would feel utterly and unquestionably real." They use the brain-scan findings to explain the interconnected cosmic unity that the Buddhists experienced, but the results could also explain what Morse calls the "universal, unifying thread of love" that people with near-death experience consistently reported.

These brain scans show that when the parietal lobes go quiet, portions of the right temporal lobe—some of the same portions that Penfield showed produced feelings of excessive religiosity, out-of-body experiences, and vivid hallucinations—become more active. Newberg and D'Aquili also argue that activities often found in religious rituals—like repetitive chanting—activate (and deactivate) similar areas in the brain, a finding that helps explain some of the more puzzling out-of-body experience reports, like those of the airplane pilots suddenly floating outside their planes. Those pilots were as intensely focused on their instrumentation as meditators focused on mantras. Meanwhile, the sound of the engine's spinning produces a repetitive, rhythmic drone much like tribal drumming. If conditions were right, says Newberg, these two things should be enough to produce the same temporal lobe activity to trigger an out-of-body experience.

Neuropsychologist Michael Persinger of Laurentian University in Sudbury, Ontario, has conducted other studies that explore the generation of altered mental states. Persinger built a helmet that produces weak, directed electromagnetic fields. He then asked over 900 volunteers, mostly college students, to wear the helmets while he monitored their brain activity and generated variations in the electromagnetic field. When he directed these fields toward the temporal lobes, Persinger's helmet induced the sort of mystical, free-of-the-body experiences common to right temporal lobe epileptics, meditators, and people who have had near-death experiences.

None of this work is without controversy, but an increasing number of scientists now think that our brains are wired for mystical experiences. The studies confirm that these experiences are as real as any others, because our involvement with the rest of the universe is mediated by our brains. Whether these experiences are simply right temporal lobe activity, as many suspect, or, as Britton's work hints and Morse believes, a whole brain effect, remains an open question. But Persinger thinks there is a simple explanation for why people with near-death experience have memories of things that occurred while they were apparently dead. The memory-forming structures lie deep within the brain, he says, and they probably remain active for a few minutes after brain activity in the outer cortex has stopped. Still, Crystal Merzlock remembered events that occurred more than 19 minutes after her heart stopped. Nobody has a full explanation for this phenomenon, and we are left in that very familiar mystical state: the one where we still don't have all the answers.