All the evidence says that it is. Despite hocus pocus claims from preachers and urban legends about people who have been to heaven and come back, there's no evidence that life goes on after death. Consciousness is dependent on physical processes. When the brain dies and the body decays, there is no longer an organized physical process, so the only logical conclusion is that there is no consciousness.

But what about near death experiences? Couldn't they be proof of an afterlife? Let's examine the evidence. All the stories are just that – stories. Anecdotal evidence, as we've seen, is extremely weak, and should only be considered when stronger corroborating evidence exists. Were the people who experienced NDEs in good mental and physical condition? Obviously not, as near death is a pretty bad situation, both physically and mentally. We know that even minute changes in the brain can trigger wildly erratic perceptions and behaviors. Dying is considerably more than a minute change in the brain. On the surface, the evidence for NDE's as proof of an afterlife seems fragile at best.

We're still not done, though. Is there better evidence that NDE's are simply physical, and that the perceptions of heaven and hell are illusions? It turns out that there is quite a lot. Before discussing NDEs directly, we need to be clear on a few terms.

If you've ever watched the movie, The Princess Bride, you will remember Miracle Max's famous words about death: “Whoo-hoo-hoo, look who knows so much. It just so happens that your friend here is only MOSTLY dead. There's a big difference between mostly dead and all dead. Mostly dead is slightly alive. With all dead, well, with all dead there's usually only one thing you can do. Go through his clothes and look for loose change.” The scientific descriptions are not as witty, but they're not radically different. There is a big difference between clinical death and brain death. Clinical death usually results from cardiac arrest. When the heart stops pumping, neurons no longer receive oxygen. Without new oxygen, they continue to fire for a short while, sometimes with odd side effects. It would only be a slight stretch to say that a clinically dead person is mostly dead.

Brain death, on the other hand, is all dead. Clinical death can be reversed within a certain time frame. We've all heard stories, and seen depictions on medical dramas. The heart can be started chemically, electrically, and manually, depending on the situation. Assuming that there is still some neural activity, starting a clinically dead person's heart will bring them “back to life.” Not so with brain death. Once the brain dies, the person is fully dead, and will not come back.

What, then, can we say about people who are clinically dead? For one thing, they are the only people who have ever had NDE's and lived to tell about them. For another, we can make some observations about what happens when the brain begins to die. If these observations form a parsimonious explanation for NDE's, we will have a compelling reason to believe they are not supernatural, and do not give proof of an afterlife.*

As the brain becomes oxygen depleted, neural networks begin to break down. Infants and small children have small neural networks. As they age, they form larger and larger networks as they process more and more information. An adult can temporarily break down access to fully formed networks by using drugs, or possibly meditative practice (although the latter is the subject of considerable debate). In fact, it's ironic that in the vernacular, many people say they have “transcendent” experiences while on mind altering drugs. The reality is that they are actually moving to a lower level of consciousness!

The sense of “loss of self” is a commonly reported experience in NDEs, and it has a well understood cause. Though the technical explanation sounds quite daunting to non-scientists, the cause is quite simple. In some cases, extreme overproduction of serotonin can inhibit the ability of neurons to pump potassium out of neural channels, effectively de-electrolyzing the neurons. In others, drugs can perform a function known as transmitter masking, essentially inhibiting the ability of transmitters to function properly by substituting an imposter chemical (such as an opiate) for the “proper” chemical. The end result is that synaptogenesis (the process of forming synapses) becomes temporarily “flooded.” In other words, new synapses are formed and then overturned so quickly that the brain becomes unable to process them effectively.

Critics will often object at this point in a conversation. After all, scientists have not explained every aspect of NDEs. In fact, most scientists are perfectly willing to admit that there are some very puzzling things about them, and the explanations are not always apparent. Hopefully, you've gotten good at spotting the fallacy. Someone who wants to believe in NDEs will say, “Since science doesn't have an answer, it must be proof of the afterlife.” This is a fallacy of ignorance, and is not valid logic. Still, many will argue that there are common threads. People from different religions have the same kinds of experiences. Kevin Nelson, a neurophysiologist at the University of Kentucky in Lexington, has this to say: "People say that because there's a common thread running through them all there must be a spiritual element," he says. "I look at that common thread and I see a biological process." (New Scientist, October 17, 2006) Nelson believes that he can explain the entire experience in purely scientific terms. He might be able to, but then again, he might miss something. This is not as relevant as it may seem. The important point is that good critical thinking demands that we not make up answers.

In fact, there is a common misconception about NDEs. It's not necessary to be at death's door to experience one. Quoting from the New Scientist article:

Nelson says that that's because despite the name, NDE has little to do with actually being close to death. He argues that the experience stems from an acute bout of "REM intrusion" - a glitch in the brain's circuitry that, in times of extreme stress, may flip it into a mixed state of awareness where it is both in REM sleep and partially awake at the same time. "The concept that our brain is either 100 per cent awake or 100 per cent in REM sleep is absolutely erroneous," says Mark Mahowald, a neurologist at the Minnesota Regional Sleep Disorders Center in Minneapolis. "We can have pieces of one state intruding into another, and that's when things get interesting."

REM intrusion is a common feature of narcolepsy - a neurological disorder characterised by uncontrollable bouts of sleep that can cause elaborate hallucinations and, sometimes, out-of-body experiences. But REM intrusion can affect anyone, and frequently does. Recent estimates suggest that up to 40 per cent of people have experienced "sleep paralysis", a form of REM intrusion in which you awaken with part of your brain still in REM sleep and your body paralysed. Often the result is a terrifying feeling of being unable to move, accompanied by visual or auditory hallucinations and pressure on the chest. Sleep paralysis has been offered as a rational explanation for many apparently supernatural phenomena, including witch attacks, visitations by the dead, and more recently alien abductions.

Scientists are experimenting with the phenomenon of out of body sight, too. Olaf Blanke, a cognitive neurologist at the Swiss Federal Institute of Technology, has caused subjects to see their legs, disembodied, from a floating perspective, simply by applying an electrical stimulus to the angular gyrus, a part of the brain involved with processing sensory information. (New Scientist)

There's yet another example of transcendental experiences that we should look at. Epileptics often report NDE-like perceptions after having particularly intense seizures. Seizures which effect the limbic system are well known for causing religious or transcendent experiences. In a way, this is an opposite cause for a similar effect. When a person has a seizure, their brain is firing too many neurons at once. Just like a computer, our brain seldom uses all of it's capacity at once. The myth that we only use 10% of our brains comes from a simple misunderstanding of this concept. When a computer is idle, or is only running a few processes, it uses a small percentage of its total processing power. Our brains function essentially the same way. Also, just like a computer, when we over tax our brains, the results are not always pleasant. How this relates to clinical death is simple. When the heart weakens, the body must compensate by increasing blood pressure drastically, keeping precious oxygen flowing to the brain. The increase in pressure wreaks havoc on the brain. Though it is still alive, it is far from normal functioning.

There is much speculation about the connection between epilepsy and religion. A nun at a Carmelite monestary in California recently discovered that the visions and transcendental raptures she'd been experiencing for years were actually epilepsy. Careful review of the private lives of many religious figures has prompted the question, were many of the prophets and religious visionaries of the past epileptics? In the end, we will probably never know about those who have long since passed. New research is coming in all the time, however, and as the connection becomes more and more concrete, it's becoming harder and harder to dismiss the evidence that NDEs, as well as mystical experiences not associated with dying, are simply misfiring neurons playing a game with our perception.

We can look at this another way. Dismiss for a moment all the possible explanations that scientists have come up with. In a recent survey, researchers found that among people who had had NDEs, a full 60 percent had sleep problems involving REM intrusion. Only 24 percent of people who had not had NDEs had similar problems. There is clearly a physical connection between REM intrusion and NDEs. Which explanation makes more sense? That there is an afterlife, and the apparent connection to sleep problems is coincidence, or that the connection is evidence of what really causes them? (http://www.msnbc.msn.com/id/12274186/)

So, in the end, we have to concede that though there might be compelling emotional reasons to want to believe in life after death, there's simply not enough compelling logical reasons. In fact, if we apply our objectivity test by substituting another trivial question, we see clearly that without the emotional tug on our reason, we would dismiss the question out of hand. There is simply no reason to believe it.