Sunday, August 18, 2013

Reports of my Near-Death Have Been Greatly Exaggerated

Stop me if you've heard this one, but there's finally a reductionist materialist explanation of the near death experience (NDE)- seriously, they mean it this time. All of these articles are loosely based on a recent publication in PNAS, which found intense, synchronous EEG activity in a sample of 9 anesthetized mice in the 30 seconds immediately following experimental cardiac arrest1. So does this unequivocally show that NDEs are the hallucination of a dying brain, or is this a kernel of interesting neurophysiology caught in a snowball of hyperbole and polemic?

For those interested in using data for illumination, not support, let's take a step back and try and put this study into context. The NDE is a complex phenomenological experience often associated with a life-threatening event. While NDEs can occur during cardiac arrest, they have also been reported in response to trauma, illness, and drownings, even when an individual may not be in mortal danger. An adequate explanation of the NDE has proven elusive, since it must account for apparent consciousness, perception, and memory during a period in which the brain seems incapable of supporting these functions.

Proposed Physiological Explanations for NDE Phenomena

Biological hypotheses proposed to account for the NDE range are usually based on a hodgepodge of superficially similar phenomenology associated with hypoxia, hypercarbia, REM intrusion, epilepsy, psychoactive drugs, dissociation, endorphins, and gravity-induced loss of consciousness, but these analogies fall apart under any scrutiny2,3. Susan Blackmore argued the dying brain hypothesis, attempting to explain NDE phenomenology as hallucinatory experiences created by a brain starved of sensory input and blood flow4. While Blackmore's ideas initially sound convincing, and they were initially an important contribution to the discussion of the NDE, the advancement of the field has really put them out to pasture2,3. Since there's not really a good materialist alternative to the dying brain hypothesis, it often gets touted as scientific consensus, irrespective of its glaring omissions, and any research which appears to support it at first glance is heralded as the explanation of the NDE.

The Borjigin et al. Study & The Dying Brain Hypothesis

If we observe coherent brain activity in rats after cardiac arrest, is this even relevant to the phenomenal experience of the NDE? First, we should note that we have no way of inferring about the phenomenal experience of rats during this burst of brain activity. Secondly, this burst of activity hasn't been seen in humans, although electrodes on the scalp are probably not as sensitive as electrodes implanted in the brain. Thirdly, even if this activity did occur in human beings, we have no idea if it is actually related to conscious experience - I'm not an expert in EEG, but I do know that synchronous activity can occur in seizures, whose phenomenology is different from the NDE.

In my opinion, this finding isn't terribly relevant to the human phenomenal experience during cardiac arrest, but it is intriguing. The brain has extremely high metabolic demands to sustain the constant depolarization and repolarization of neurons. We shouldn't expect an immediate, complete abolition of brain activity after cardiac arrest, but the synchronicity of the activity is very intriguing. It's also interesting to note that even when implanted EEG electrodes were used, giving us one of the best windows into brain activity, all coherent activity was abolished within 30 seconds of cardiac arrest, which is consistent with research in humans. It appears that any sustained consciousness, perception, and memory after this period would not be explained by a neural basis.

If this activity does occur in some or all humans after cardiac arrest, does this explain the NDE? Not really, since the NDE can occur in the absence of injury, and can be shared between individuals, all of which argues against the dying brain hypothesis2,3,5. It also makes one wonder how a very brief flurry of neural activity could be responsible for both generating a vivid conscious experience while simultaneously encoding it in memory for later recovery, especially when trauma to the brain is typically associated with both absence of consciousness and loss of memory2.

Principle of Charity - Does This Explain The NDE?

Let's grant those seeking to bolster the dying brain hypothesis with the results of the Borjigin et al. study a couple premises, which in my opinion, are not well supported to date:
  1. The coherent activity observed in rats was associated with conscious experience
  2. Similar activity occurs in humans, but has not been observed due to measurement limitations
  3. The experiences associated with the NDE occur in this burst of activity
Aside: If someone can explain how we're to soundly infer about the phenomenal experience of rats from their EEG, I'm sure Thomas Nagel would have your full attention.

The NDE is not just the "experience," as one of the thorniest issues is how individuals with severely compromised brain function are able to not only have conscious experiences, but have accurate memory and perception. Furthermore, this apparent veridical perception (AVP) can occur in individuals whose eyes were covered in gauze in preparation for surgery, the comatose, and even those blind from birth2,3. If NDEs were just hallucinatory experiences of a dying brain, it seems unlikely that they'd occur in the absence of injury, be consistent with reality, and potentially even shared between multiple people5.

Common "explanations" for apparent veridical perception are based on the assumption that while brain activity on the cortical surface may be abolished, there might be deep brain activity which could somehow explain the phenomena. Research in humans and this latest study in rats demonstrate that even when electrodes are implanted in the brain, it appears that EEG activity is abolished within 30 seconds of cardiac arrest, arguing against deep brain activity as an ostensible explanation of AVP.

So What Have We Learned Today?

In summary, the Borjigin et al. study is quite intriguing, and a valuable addition to the neurophysiology and NDE literature. Like most studies into a complex, interesting phenomenon, it raises far more questions than it does answers. Unfortunately, it appears that a level-headed discussion of this finding in the context of the larger picture hasn't happened yet, and that's quite disappointing. Even when we grant several unsupported premises to the dying brain hypothesis, it still doesn't adequately explain the NDE2,3. This latest finding is not germane to NDEs occurring in the absence of injury, and may even argue against the dying brain hypothesis in some well documented accounts, such as those of Al Sullivan and Pam Reynolds.

Take note, pop-sci "journalists," this is how it's done. Since you're paid by the click, I know you're not about to let a body of research get in the way of a good sensationalist headline.

1. Borjigin J, Lee U, Liu T, Pal D, Huff S, Klarr D, Sloboda J, Hernandez J, Wang MM, Mashour GA. Surge of neurophysiological coherence and connectivity in the dying brain. PNAS USA. 2013 Aug 12.

2. Holden JM, Greyson, B, and James D, eds. The Handbook of Near-Death Experiences: Thirty Years of Investigation. Santa Barbara, CA: Praeger, 2009.*

3. Carter C. Science and the Near-Death Experience: How Consciousness Survives Death. Toronto: Inner Traditions, 2010.

4. Blackmore S. Dying to Live: Near-Death Experiences. London: Grafton, 1993.

5. Moody RA and Perry P. Glimpses of Eternity: Sharing a loved one's passage from this life to the next, New York, NY: Guideposts, 2010.

* I can't recommend this book highly enough: if you're genuinely interested in learning about the NDE, this book is truly unparalleled - Before anyone publishes another "explanation" of the NDE, you should learn from those who have been researching the topic for decades.

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