August 12, 2013

expert reaction to new study in rats of neurophysiology and the dying brain

A PNAS study found electrical activity in the brains of rats for a brief period after their hearts had been stopped, which the authors suggested could shed light on reports of near-death experiences in humans.

Dr Sam Parnia, Visiting Fellow at the University of Southampton, said:

“The authors have demonstrated some electrical activity in the brain in nine rats a number of seconds after their hearts had stopped.  In the introduction they suggest that this type of EEG activity is associated with conscious thought processes in humans.  However, the assumption that this pattern of EEG processing at the time of cardiac arrest also occurs in humans and in particular is associated with the occurrence of NDE is extremely presumptive and unsupported by evidence.  In other words, they are taking the observations made but going beyond the data and linking it to something for which there is no data or evidence and certainly none from their study.”

Dr Martin Coath, Public Engagement Research Fellow at the Cognition Institute, Plymouth University, said:

“This new research is genuinely interesting, but the conclusion that these are ‘neural correlates of heightened conscious processing’ isn’t strongly supported – unless you take it to mean ‘more of some types of activity that are associated with being awake’ which is a bit of a stretch.”

“As the induced cardiac arrest happens while the rat’s brain is anesthetised, the results show the response of an unconscious brain to critical lack of blood flow and oxygen.  It is certainly interesting that this causes some types of activity in the brain to increase in a predictable and coordinated way well after the heart has stopped – but hardly surprising.”

Dr Anders Sandberg, James Martin Research Fellow at the Future of Humanity Institute, Oxford University, said:

“This is a nice experiment.  It is a simple and obvious test, and seems to be well done.  As the authors note, not much research has been done on brains suffering from heart failure – there might be many other important things to learn here, from a purely medical standpoint.

“EEG tells us things about brain activity a bit like listening at traffic noise tells you what is going on in a city.  It is certainly informative, but also an average of a lot of individual interactions.  And it is quite possible that different underlying situations can cause similar-looking brain activity.  So while particular brainwaves correspond to certain brain states in normal, healthy brains, it is not obvious they correspond to the same thing in a dying brain.

“Gamma waves have been linked to consciousness in various neuroscientific theories of consciousness.  The idea is that this fast rhythm helps synchronize different neural networks and bind their experiences together into consciousness.  There is plenty of debate about this, and many scientists and philosophers are unconvinced that this either works as an explanation (how does synchrony of your neurons actually make you experience something?) or that gamma waves imply consciousness (maybe they just imply that processing is happening, and that processing is what causes consciousness).

“A lot of the neural networks in the brain can stimulate themselves without any external signals under the right conditions – typically when regulation is not working well, like under the influence of drugs, tiredness etc.  And oxygen deprivation can certainly mess up many systems at the same time.  The gamma rhythm is also a bit of a ‘resonant frequency’: many parts of the brain tend to oscillate naturally at this frequency.  So it could be that during a NDE the conditions make neurons start to fire and form patterns of activity. These patterns of activity are shaped by how the brain is connected, and we know that some patterns in the visual cortex seem to closely correspond to commonly reported hallucinations (like tunnels).  Higher order parts of the brain might create emotions or ideas in a similar random fashion, populating the experience.

“No doubt some people will presumptuously claim that this is further evidence for life after death, which is doubly silly (near death experiences are in themselves just experiences).  But if one believes that, then one should also conclude the afterlife includes a lot of lab mice.”

Dr David McGonigle, Lecturer at Cardiff University, said:

“Do we know if animals experience ‘consciousness’?  Most philosophers and scientists are still at loggerheads over what the term refers to in humans, let alone in other species.

“While recent research now suggests that animals may indeed have the kind of autobiographical memories that humans possess – the kinds of memories that allow us to place ourselves in a certain time and place – it seems unlikely that near death experiences (NDEs) would necessarily be similar across species.

“The authors’ finding – that the rodent brain displays highly coherent patterns of gamma frequency activity following cardiac arrest – is extremely intriguing: one might expect there to be a general loss of synchrony after such a catastrophic event.  However, the paper has merely shown – and the authors are extremely clear on this point – that they have demonstrated the change in gamma oscillations occurring over a similar time period to when NDEs are experienced in humans.  We have no idea what the rats experience – if anything – while the increase in synchronous gamma occurs.  Seeing if NDEs can be triggered by neurostimulation using experiments that induce increased gamma synchrony in humans might represent a way to go beyond correlation to causation’.”

Dr Chris Chambers, Senior Research Fellow at Cardiff University, said:

“This is an interesting and well conducted piece of research.  We know precious little about brain activity during death, let alone conscious brain activity.  These findings open the door to further studies in humans.

“It is tempting as it would be to draw a link between this surge in neural activity and consciousness, but there are two barriers to doing so.  The first is that we don’t know to what extent rats experience consciousness at all, so we don’t know what the activity means.  Second, even if rats are conscious, to conclude from their brain activity alone that these bursts of activity reflect consciousness (without measuring it behaviourally) would be a logical fallacy known as reverse inference.  To overcome these limitations we would need to run a study in humans and relate the changes in activity to what they report about their conscious experience. 

“Finally, we should be extremely cautious before drawing any conclusions about human near-death experiences: it is one thing to measure brain activity in rats during cardiac arrest, and quite another to relate that to human experience.”

‘Surge of neurophysiological coherence and connectivity in the dying brain’ by Jimo Borjigin et al. published in PNAS on Monday 12th August.