The Science of Consciousness:
Chapter 10: Consciousness and the Brain
What this chapter is about: How is consciousness related to the brain?
What are the neural correlates of consciousness (NCCs)?
Perhaps "Consciousness and the brain" was a slightly misleading title for this chapter, because it also includes discussion of neurotransmitters. "The biology of consciousness" is a more general title, but then related material appears in other chapters too, such as the chapters on , , and , among others. Oh well. The material has to be organised somehow.
p. 258. Figure 10.8 legend says "Death corresponds to being permanently at the origin". That isn't right - death corresponds to maximum unconsciousness and zero arousal, so is in the furthest bottom left of the graph, more extreme than coma. I should add the graph is schematic and there are no units for degree of consciousness or arousal. Perhaps the graph would be clearer as a standard graph rather than overlapping x and y scales with four quadrants.
p. 258. "As far as we can tell, only humans have knowledge of death and its certainty." This statement is too strong. I meant (probably) only humans know that they are going to die, and all that death entails. I did not mean to imply that some animals do not missed dead others, or do not grieve (see below).
Chaudhary, U., et al. (2017). Brain-computer interface-based communication in the completley locked in. PLoS Biology, 1-25. Cited on p. 262 in the section Locked-in Syndrome. This paper has since been retracted by the journal - but not by the authors, who stand by their results and methods.
See here at . The retraction doesn't change the sense of the section of my book, and there are similar results in line with the original findings (see for example references below).
It is well know that some animals appear distressed when they have lost others close to them, such as mates and children, and show signs of mourning and grief. The examples commonly given are non-human primates and elephants (with grief in elephants noted by Pliny the Elder, 23-79AD). And we have all heard of dogs pining after the deaths of their humans.
In 1972 the primatologist Jane Goodall witnessed a young male chimp named Flint die a month after the death of his mother, Flo. The male appeared so despondent that he stopped eating and socialising.
Links to work on animal bereavement and grief
The is very informative.
Anderson, J.R., Biro, D., & Pettitt, P. (2018). Evolutionary Thanatology. Philosophical Transactions of the Royal Society B: Biological Sciences, 373, no. 1754,: 20170262. https://doi.org/10.1098/rstb.2017.0262. Evolutionary thanatology, ways of dealing with death across species and evolution.
King, B.J. (2013). How animals grieve. Chicago: University of Chicago Press.
Swift, K., & Marzluff, J.M. (2018). Occurrence and variability of tactile interactions between wild American crows and dead conspecifics. Phil. Trans. R. Soc. B 373: 20170259. http://dx.doi.org/10.1098/rstb.2017.0259. How crows react to dead crows nearby.
Fear of death
I admit to being morbidly obsessed with what happens when we die. But death is, we assume, eventually the final loss of consciousness, so the study of death and dying is informative for understanding consciousness. Notice I say “eventually”; that’s because we have to define death, and different people have different definitions. If you define death as the permanent cessation of all respiratory and cardiac function the brain continues to function for a while after that. And if you talk about brain death, what about different parts of the brain dying at different rates? What if the brainstem is still functioning while higher functions have ceased? I cover all these topics in the book.I don't know why more people aren't scared of dying. I'm terrified of my death (and of loved ones, including Beau), to the extent that yes, it interferes with my quality of life. I have thanatophobia. asserts that this phobia generally peaks in one's twenties and then declines, but sadly I am older than that, and the older I get the more intense my fear becomes. I think the fear of a loved one dying and fear of my own death are related but distinct. Most people are scared of a loved one dying, but I think I worry about it more than most. It is however the fear of my own death that obsesses me most. How can there be a world without me? Being told that there was a world before me that got along perfectly well doesn't help. And what is it like never to wake up? Why don't you people worry that you might not wake up tomorrow? How can you all be so - unconcerned? I know in principle it's like falling into a dreamless sleep for ever, and therefore not like anything, but that doesn't help me either. And talking of Beau, I'm pretty sure he's not afraid of dying. Never say ever, but I doubt very much that any animal has ever been afraid of dying; perhaps fear of death is what makes humans unique among animals (see ). See my blog post for more on .
In 2019 I had a minor operation on my wrist, and for the first time in living memory was given a general anaesthetic. It was propofol, and I tried to count down and resist while going under. It was of course hopeless, and after about four seconds succumbed. For me it was like going into a deep dreamless sleep. I woke up 45 minutes later feeling bright and breezy. I had had gas (nitrous oxide) many decades ago at the dentist, but don't remember much about it, other than counting to ten and reaching four before waking up with everything done. I don't remember feeling odd waking up then, either. My experience is different from that of others: Anil Seth in his excellent "Being you" (review coming soon) says:
"So I returned, drowsy and disoriented but definitely there. No time seemed to have passed. Waking from a deep sleep, I am sometimes confused about the time, but there is always the impression that at least some amount of time has gone by, of a continuity between my consciousness then and my consciousness now. Under general anaesthesia, things are different. I could have been under for five minutes, five hours, five years - or even fifty. And 'under' doesn't quite express it. I was simply not there, premonition of the total oblivion of death, and, in its absence of anything, a strangely comforting one."
Perhaps it's my experience of dreamless sleep which is odd. I say "odd" but I really don't know whose experience is most common - and there's certainly no right or wrong here.
Further references on anaesthesia
Suzuki, Mototaka, and Matthew E. Larkum. (2020). General Anesthesia Decouples Cortical Pyramidal Neurons. Cell, 180, no. 4, 666-676. e13. https://doi.org/10.1016/j.cell.2020.01.024.
While the neural correlates of consciousness (NCC) are concerned with which brain structures are involved in generating and maintaining consciousness, the biological correlates of consciousness (which we might term BCC) are concerned with a yet lower level, at the synaptic and neurotransmitter levels. The term molecular consciousness has come into use for the way in processes beneath the level of brain structures might be involved in consciousness.
Note that the term molecular consciousness refers to the role of the molecular level in generating consciousness, not consciousness at the molecular level (which does make some sense in the context of panpsychism. See Chapter 2 on reductionism.
Bickle, J. (2006). Reducing mind to molecular pathways: explicating the reductionism implicit in current cellular and molecular neuroscience. Synthese, 151, 411–434.
Building a brain
The is attempting to create a digital reconstruction of the mouse brain. The project is ongoing and dependent on supercomputers.
Markram, H. The Blue Brain Project. Nature Reviews Neuroscience, 7, 153–160 (2006).
Links to research on dying
Coma. . Murina Abdulla was 32 when she was involved in a traffic accident in 1991. She was diagnosed as being in a vegetative state and moved around hospitals before being given therapy in Germany. In 2018 she said the name of her son, Omar (who was four at the time of the accident). She become more responsive, can carried out limited conversation, and feel pain.
. In The Times, "Thousands of people thought to be in a vegetative state are awake and locked in unresponsive bodies, experts in the field say. ... Research studies have shown that using MRI scans or bedside electroencephalogram (EEG) can detect consciousness in some men and women thought to have no awareness of what is going on around them. Techniques include asking them to visualise a face or a house, which activate different areas of the brain, or seeing if their brain patterns echo those measured in fully conscious audiences." See: Scolding, N., Owen, A. M., & Keown, J. (2021). Prolonged disorders of consciousness: a critical evaluation of the new UK guidelines. Brain, 144, 1655-1660.
One last act of love. A book by Cathy Rentzenbrink (Picador, 2015) on PVS, its effects on loved ones, and the problems they face and difficult decisions they have to make. Very moving and very revealing.
The great beheading controversy
Some, perhaps many people are fascinated by the macabre topic of whether and how long people live after being beheaded. As soon as I tell people what my book is about it's a reasonable bet people will ask about it. I've even had conversations in bars about it. Of course by "how long people live" people are really interested in the question of how long a person remains conscious. The topic is covered in my book, but the short answer is that while of course we can't be sure, it's probably a few seconds before blood pressure drops for consciousness to be lost (estimates range from two to seven). And no, they will most definitely not be a pleasant few seconds, near-death experiences aside. The guillotine is "better" than being beheaded with an axe or sword, when the executioner might need several attempts to get it "right".
Severing the jugular leads to a rapid cessation in oxygen flow to the brain. It's different from drowning or suffacation, which also ultimately result in brain death due to oxygen deprivation because it will take some time for the oxygenated blood in the body to be fully depleted.
If you know more about this topic, please let me know, so that I can have even livelier conversations in bars. Meanwhile here are some links to the subject - obviously it's a gruesome subject that might upset some so please use your discretion if you want to look, although I don't think there's anything anyone would consider offensive. They're all reputable sites.
Covers whether Anne Boleyn really tried to speak after execution and Mike the Headless Chicken.
. Electrical activity persists for 10-15 seconds in a decapitated rat brain, but large, slow waves are observed 50-80 s after decapitation: the "wave of death" associated with mass neuronal depolarisation as neurons lose their electical abilities.
van Rijn, C. M., Krijnen, H., Menting-Hermeling, S., & Coenen, A. M. L. (2011). Decapitation in rats: Latency to unconsciousness and the “wave of death.” PLoS ONE, 6(1), 1–6. https://doi.org/10.1371/journal.pone.0016514
Kongara, K., McIlhone, A.E. Kells, N.J., & Johnson, C.B. (2014). Electroencephalographic Evaluation of Decapitation of the Anaesthetized Rat. Laboratory Animals, 48, 15–19. .
N.G. Gregory, S.B. Wotton (1984). Sheep slaughtering procedures. II. Time to loss of brain responsiveness after exsanguination or cardiac arrest. British Veterinary Journal, 140, Issue 4, 54-360. . Gives a time of 14 seconds for severing both carotid artieries in sheep.
Roberts, T.D.M. (1954). Cortical activity in electrocuted dogs. Vet. Rec 66: 561-567. Suggests about 12 seconds for dogs.
H. McIlwain & H S Bachelard. (1985). Biochemistry and the central nervous system (fifth edition). Churchill Livingstone, Edinburgh. ISBN 0-443-01961-4. States the human brain has enough stored oxygen for seven seconds of metabolism.
Further references on death
Norton, L., Gibson, R. M., Gofton, T., Benson, C., Dhanani, S., Shemie, S. D., … Bryan Young, G. (2017). Electroencephalographic Recordings during Withdrawal of Life-Sustaining Therapy until 30 Minutes after Declaration of Death. Canadian Journal of Neurological Sciences, 44, 139–145. https://doi.org/10.1017/cjn.2016.309
Vrselja, Z., Daniele, S. G., Silbereis, J., Talpo, F., Morozov, Y. M., Sousa, A. M. M., … Sestan, N. (2019). Restoration of brain circulation and cellular functions hours post-mortem. Nature, 568 (7752), 336–343. https://doi.org/10.1038/s41586-019-1099-1
Further reading on dying
Crowley, A. (1913). The testament of Magdalen Blair. In my opinion the best fictional account about the process of dying and being dead - and it's not portayed as a pleasant experience.
Shafak, E. (2019). 10 minutes 38 seconds in this strange world. London: Penguin. Set in Turkey, this short-listed for the Man Booker Prize, this novel describes the final moments of consciousness of a person after death. The title refers to the length of time the protagonist has awareness and memories after "death", although I am unable to find any reference supporting the idea that any brain processing persists this long. It's a curiously precise time.
Michael, P. (2020). Neurothanatology: The quest for the NDE-ogen. The Paranormal Review, 95, 14-16. This short review examines the supposed similarities between DMT (dimethyltryptamine) "trips" and NDEs (near-death experiences).
Li, D., Mabrouk, O. S., Liu, T., Tian, F., Xu, G., Rengifo, S., … Borjigin, J. (2015). Asphyxia-activated corticocardiac signaling accelerates onset of cardiac arrest. Proceedings of the National Academy of Sciences of the United States of America, 112(16), E2073–E2082. Asphyxia brings on a flood of neurotransmitters and increases electrical coherence in rat brains, markers of possible enhanced cognitive activity (relating to NDEs in cardiac arrest).
Further references on cortical-thalamic loop and brain connectivity
This is definitely a growth area and we are still learning.
Afrasiabi, Mohsen, Michelle J. Redinbaugh, Jessica M. Phillips, Niranjan A. Kambi, Sounak Mohanta, Aeyal Raz, Andrew M. Haun, and Yuri B. Saalmann. (2021). Consciousness Depends on Integration between Parietal Cortex, Striatum, and Thalamus. Cell Systems, 12, no. 4,363-373.e11. https://doi.org/10.1016/j.cels.2021.02.003.
Further questions to think about
1. What ethical issues are raised by being able to read people's thoughts by brain imaging, and how should any issues be resolved?