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Rodent asphyxial cardiac arrest study finds highly coherent brain activity
#1
Important and interesting study of rodent brain activity using an asphyxial cardiac arrest model published April 2017. It shows interesting neural correlates of consciousness at near electrocerebral silence.

In cases of abrupt loss of blood circulation from cardiac arrest, a silent scalp EEG is reported to occur within 30; conversely, in cases of a gradual loss of blood flow, such as hypoxic respiratory failure, the EEG has been found to become isoelectric before cardiac arrest.

This study was investigating the latter, and they found asphyxial cardiac arrest induced a period of near-electrocerebral silence that was marked by increased phase coherence in the frontal lobes (motor cortex) and increased power in the rear visual cortices, both of which look like potential markers of consciousness.

[Image: phase_coherence.jpg]


Fig 3. ECoG phase coherence during asphyxial CA. (A) During AS3, the interhemispheric frontal coherence from 13 to 39 Hz (i.e., beta and slow gamma) was significantly greater (p < 0.05) than during the period immediately before asphyxia (i.e., washout). (B–D) The coherence during AS3 in the other channel combinations was not significantly greater than washout. The coherence during AS4 was largely an artifact of the ECG signal penetrating the ECoG. Data shown as mean of n = 16 rats. Dotted lines indicate region of statistical significance. *p < 0.05 by paired two-tailed nonparametric permutation test. ECG, electrocardiogram. Color images available online at

Link to the paper...

Neural Correlates of Consciousness at Near-Electrocerebral
Silence in an Asphyxial Cardiac Arrest Model


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5399737/

Definitely worthwhile reading, particularly the discussion section, which is peppered with interesting references to other important papers.
 
More detail....

This invasive EEG (iEEG) study measures highly coherent firing in the motor cortex, together with increased power at higher frequencies in the visual cortex, at the same time as normal medical scalp EEG shows silence.

That's important, because it appears to confirm the results of other studies which also show the temporary reappearance of conscious-like firing activity, at the same time as the brain's own EM field loses power.

As I said in the thread you linked to, the only correlation I can find with all these NDE OBEs (& OBE's generally) - where there is recall of apparently accurate objective information - is when the brain's EM field power drops.

If we're still able to measure this spontaneous re-emergence of firing activity using crude metal probes, then I think the activity is probably powerful enough to be responsible for at least the OBE component of the NDE.

All my research points at the brain's networks being able to temporarily resynchronise and become entrained by compatible external EM fields, when it's own EM fields drop.

I suggest the brains networks can act like a humongous stochastic amplifier of compatible external EM fields, when it's own sensory input/output falls.

I suggest it may be no coincidence that both motor and visual correlated firing activity were temporarily measured in these energy compromised rodents brains.

Borjigin found similar firing activity which also spontaneously re-emerged after sudden cardiac arrest. This also *strongly* resembled the firing activity we measure in wakeful humans and apes who are undertaking a visual task. In her experiment, measured firing activity had got all screwed up from going into cardiac arrest. But as the rodents lay dying, all that crazy jumbled up firing suddenly disappeared, and the rodents suddenly showed activity that looked *more* conscious than their normal wakeful activity. Indeed whilst the rodents were dying, time after time the jumbled up measured activity, suddenly and bizarrely changed to resemble the firing activity we would expect to see going on in the researchers own brain whilst they are conducting the experiment [Image: clear.png]

This study seems to have found similar activity.

I'd love the researchers to repeat these experiments, this time placing one group of dying rodents in a magnetically shielded box, whilst the other group is placed in a faraday cage as usual, with researcher conducting the experiment right next to the rodent.

I'm betting they won't measure the same firing activity in both groups. Which would suggest that the firing activity they are measuring is modulated by external magnetic fields.

Update

Also, going right back to the early days of EEG, we've known that measured frequency bands can decrease in Electromagnetic (EM) field power (that is become suppressed) in response to a variety of different tasks. Nowdays, event related frequency band power changes are measured using Event Related Desynronisation (ERD). ERD is defined as the percentage of increase or decrease in a frequency bands power during a test period, when compared with a reference period which precedes the event (the stimulus).

Crucially for me, the research shows that desynchronisation appears to be related to the relevance and/or difficulty of a task. The more demanding or relevant a task, the stronger the amount of alpha suppression or ERD. This certainly seems to include stressful situations, and although I've not come across any real world studies, I'd expect to see a large negative ERD in real world events... like falling when climbing etc.

Also on the subject of a release of chemicals in the brain, Borjigin's second study did show a massive increase in released chemicals, some of which are believed to be important to memory formation. It's worthwhile considering whether this sudden saturation of chemicals might increase the speed and reinforcement of memory creation, and might perhaps be part of the explanation as to why these experiences can 'stick' so strongly in experients memory, even after many months or years, their recalled experiences often don't seem to alter too much from their initial recollection.

Finally when thinking about chemicals, nowdays we know that chemical reactions can actually be described more accurately at a fundamental level using quantum mechanics (quantum laws of motion). If you've ever seen the Tufts research on the 'electric frog face' where an electrically sensitive dye reveals the tadpoles face, before the tadpole is physically formed, you'll probably realise that what chemicals in the brain are actually doing, is really about charges and fields, and possibly better described as modifying EM activity. So for me at least, we land right back at EM fields...
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