Max_B
Member
I've had a bit more time to process that 2012 paper. To me, Bernardo's error is to assume that reduced CBF to those parts of the brain found in the study represent some sort of neural correlates of consciousness, whereas all they really represent are neural correlates of psilocybin use.
Careful reading of this passage is key IMO:
Yeah, I agree, and what is really being observed is psilocybin's affect on their measurements... I stress 'measurements', because it's not known what neural activity BOLD is really correlated with.
Refreshing my understanding of fMRI BOLD this morning...
BOLD itself Is not really measuring oxygen use... CBF is thought to be related to neural activity... But BOLD is taking advantage of our knowledge that when CBF increases, it increases beyond the brains metabolic rate of oxygen utilisation (CMRO2). This causes a rise in localised capillary and venous oxygen levels.
It's that mismatch between CBF increase and CMRO2 change that the BOLD signal is related to.
Thus BOLD is reliant on knowing what neural activity is going on in the brain, to be able to make any assumption on what these measurements mean.
You can quickly see that a variety of changes could affect the BOLD 'mismatch' signal, that are not related to an increase in oxygen utilisation.
Irrespective of that, I still return to this odd assumption that 'richness' of experience somehow requires an increase in energy utilisation (now further confabulated by whether BOLD actually means that in this case) which makes very little sense to me.
Borjigin's study was conducted in an enforced physiological state of zero CBF, and therefore substantially reduced EM power measured by iEEG... and in that physiological state, she measured increased synchronization and connectivity which she states makes the organism appear *more* conscious during cardiac arrest, than during wakefulness.
I can't see anyway round that, which suggests one should be very careful about suggesting CBF is any sort of reliable measure of 'richness', irrespective of what BOLD means in this case regarding actual energy utilisation.
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