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Split Brain Does Not Lead to Split Consciousness
- advisedwang 10y agoInterestingly this work contradicts not just previous theory, but also previous experimental result. I would be interested to see if they have a critique for why the previous runs of the experiment provided a different experimental result.
- joeyo 10y agoThey discuss a few possibilities. The first is cross-cueing, which they describe as " ... behavioural tricks, such as touching the left hand with the right hand" [1]. However, they also discuss a number of reasons why they think cross-cueing did not play a role. The second (and imho quite interesting) explanation is that the split-brain phenomenon could be transient: their subjects have had between 10 and 20 years to recover since their callosectomy. It may be that the brain learns to use other pathways to communicate inter-hemispherically. 1. https://doi.org/10.1093/brain/aww358 https://doi.org/10.1093/brain/aww358
- taneq 10y agoI think your second explanation is probably right. We keep discovering that brains are more adaptable than we previously thought. I wouldn't be surprised if their brains had learned to 'route around' the damage in some way over the years.
- summarite 10y agoVery interesting. I'm also wondering whether we might just be approaching this with too much b/w thinking - it might simply differ widely between individual patients. The operation was done by only a small number of doctors, so it might well be that each set of patients (regionally somewhat separate) has slightly different results. Or even that each individual differs - they weren't operated with modern precision and even with modern techniques you likely still would get slightly different operation results on each attempt. For the second suggestion to be tested they would have to identify someone who was tested 10/20/30/40 years ago and try to repeat the experiment. One last thought: that information flows between brain halves doesn't exclude the possibility of there still being some disconnect and/or even two 'personas'.
- jdpigeon 10y agoThat was where my mind went as well. We can't ignore the incredible feats of neuroplasticity that undoubtedly happen in a split brain patient over a decade.That would make an interesting body of work in and of itself.
- jdpigeon 10y agoThat was where my mind went as well. We can't ignore the incredible featss of neuroplasticity that undoubtedly happen in a split brain patient over a decade.That would make an interesting body of work in and of itself.
- Zigurd 10y agoThat's what leapt out at me. These brains have had years and maybe decades to learn to reunify themselves. Split brain experiments have always shown a strong drive for presenting a unified personality even as the experiments showed a non-unified experience and response. So even if neuroplasticity in the cranium can be ruled out, the "bandwidth" and subtlety of cross-cueing, or some unknown means of communication, might have grown.
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- hathawsh 10y agoGoogle cached version, while the site recovers: http://webcache.googleusercontent.com/search?q=cache:http://neurosciencenews.com/split-brain-consciousness-6011/ http://webcache.googleusercontent.com/search?q=cache:http://...
- nicklovescode 10y agoMy knowledge of neurobiology is weak. Having received a full callosotomy, how are the hemispheres able to communicate even at 1 bit / s? Secondly, how is that estimate generated?
- kamac 10y agoFast google search provides us with an answer: > After the operation the brain has much more difficulty sending messages between the hemispheres. Although the corpus callosum is the largest white matter tract connecting the hemispheres, some limited interhemispheric communication is still possible via the anterior commissure and posterior commissure.
- cpncrunch 10y agohttps://en.wikipedia.org/wiki/Corpus_callosotomy https://en.wikipedia.org/wiki/Corpus_callosotomy "Although the corpus callosum is the largest white matter tract connecting the hemispheres, some limited interhemispheric communication is still possible via the anterior commissure and posterior commissure."
- colordrops 10y agoTwo people in the same room can communicate information at far more than 1 bit/s even without speaking, and they aren't even in the same body. I could imagine that receiving very similar inputs and observing reactions to the movements and other actions taken by the other side could also act as a high-rate channel of information.
- SlyShy 10y agoAs I understand it, they have most of the other pathways in the entire nervous system to communicate through.
- phkahler 10y agoThat 1 bit per second made me laugh. The author is clearly trying to make a name for himself. Awareness of the location of something is extremely far removed from consciousness. I wouldn't put much weight on this one.
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- amelius 10y agoHow does a brain split operation work exactly? Do they put a barrier between the two halves? Otherwise, I would expect that signals could still propagate: cut two nerves, then push them together, and I can imagine that a signal can still pass through; if not always, then in a percentage of cases.
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- gravity13 10y agoThis is an interesting question. I'm not a neuroscientist or anything, but I'd wonder how this question relates with brain waves, as well. I guess there's research into how these signals cause integration within the brain http://www.nature.com/nrn/journal/v2/n4/full/nrn0401_229a.html http://www.nature.com/nrn/journal/v2/n4/full/nrn0401_229a.ht... - I guess I'll check back here in a couple hours and hope somebody's chimed in.
- jayajay 10y agoexaclty my thoughts, it seems a bit strange to claim "completely isolated" and "virtually no" communication.
- mattkrause 10y ago> cut two nerves, then push them together, and I can imagine that a signal can still pass through If only.... Getting neurons to regrow or fuse, particularly in the central nervous system, is one of the biggest open challenges in neuroscience. If it were actually that easy, spinal cord injuries would be a thing of the past.
- corvus_sapiens 10y agoThere are 250 million neurons in the corpus callosum, each with a diameter on the order of microns. Individually, each one transmits a very primitive signal (think biological bit) that doesn't mean much without the other millions of neurons. It's extremely complex and thus extremely frail. If the cut halves on both sides don't line up exactly, you have the equivalent of static. You wouldn't mash two cut ends of normal data cables together, and there are only on the order of 100 "neurons" there. What you say is theoretically possible if the neurons weren't living cells and humans had the technology to reconstruct the brain's wirings. Your body isn't going to figure out which "wire" connects to which on its own.
- stefantalpalaru 10y agoTake that, Sam Harris! In "Waking Up: A Guide to Spirituality Without Religion" he wrote a bunch of silly stuff - thoroughly referenced with cherry-picked scientific articles - about the split brain. He went as far as estimating the amount of data passing through the corpus callosum when we don't even have a computational model for the brain. It was almost as ridiculous as claiming that the self is an illusion because we can experience its apparent dissolution.
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- terminado 10y agoNext question: is it possible to split consciousness at all?
- rixed 10y agoYou mean, between several "individuals"?
- praptak 10y agoSimilar question - how can an observer discern two consciousnesses that communicate somewhat (like two people talking to each other) from a single consciousness?
- lgas 10y agoYou might be interested in Tulpas.
- randcraw 10y agoFabulous question. I believe not. The only mammalian model that makes sense to me requires there to be only ONE point of central executive in the brain. If more than one could arise, you'd have chaos. All coordination of bilateral activity would be impossible, much less the initiation of action or a chain of perceptual focus or cognitive reasoning. With all animals above worms having bilateral symmetry, the introduction of one side becoming dominant must have ocurred very early in evolution. Thus ALL species with any cortex at all must have circuitry that prevents the bigger parts the nervous system from becoming fully decoupled and 'going' rogue.
- _saturnine 10y agoLast year I watched Dr. Gazzaniga's 2009 Scotland lecture series on Youtube. I noticed an inconsistency that bothered me enough to email him, but never got a reply. In his third Edinburgh video lecture[1], he shows two videos featuring patient J.W. In the second video, the test flashes RED and BANANA to his left and right hemispheres, respectively, and J.W. is asked to draw what he sees. He then proceeds to pick up the red pen with his left hand. But, the hand's controlling hemisphere only saw BANANA. How did it decide to pick up the red pen? Similarly, in the first video, the words MUSIC (L) and BELL (R) are flashed. He's asked to point to a picture of what he saw and he uses his right hand to point to BELL, but its controlling hemisphere only saw MUSIC. [1] https://youtu.be/mJKloz2vwlc?t=1113 https://youtu.be/mJKloz2vwlc?t=1113
- boomboomsubban 10y agoEven the earliest teats showed there was still some communication between the two halves,the tactile test from the original paper showed that the subject could not describe an object that only the left hand could feel, but they could point it out.
- _saturnine 10y agoRight, in callosotomy patients there's some level of information exchange via secondary pathways. In particular, one of Gazzaniga's experiments showed transfer of emotions.
- mrdmnd 10y agoI thought this was an Jepsen-style article on some distributed systems at first.
- Shish2k 10y agoWho says it isn't? ;)
- jeffamcgee 10y agoI don't think the IRB would take too kindly to running Jepsen-style tests on human brains.
- incompatible 10y agoI'm not sure that this proves that there's a single consciousness. There may be a second consciousness that is receiving some information about observations from the other hemisphere.
- roywiggins 10y agoI can't prove you don't have two consciousnesses either, or maybe we all do and just don't notice.
- ci5er 10y agoYou can't even prove GP has one!
- umberway 10y agoI agree. The best that can be said is something about communication of information between different parts of the brain. But my reason is more fundamental: we don't understand what consciousness is yet. Hence we can't know what questions about 'it' are meaningful let alone what conclusions to draw.
- c3534l 10y agoThat was already known, too. It does show that it doesn't create two completely equal, completely functional consciousnesses. But the problem with brain damage is people tend to also lose the ability to recognize that an ability is missing, so we can't just ask peóle "are you a little less conscious than you were before we took out that part of your brain?"
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- otto_ortega 10y agoIf you just learned that "Split Brain" was thing, I recommend watching this video by GPGrey, one of the best educational channels on YouTube: https://www.youtube.com/watch?v=wfYbgdo8e-8 https://www.youtube.com/watch?v=wfYbgdo8e-8
- mwpmaybe 10y agoThis is giving me the heebies and the jeebies.
- jayajay 10y ago> virtually eliminates all communication between the cerebral hemispheres, thereby resulting in a ‘split brain’ > their cerebral hemispheres can hardly communicate with each other and do so at perhaps 1 bit per second "Virtually all"? "Perhaps 1 bit per second"? Is it definitive that the corpus callosum accounts for exactly 100% of hemisphere communication? I am too skeptical that the brain could be that simple. > The [previously] established view of split-brain patients implies that physical connections transmitting massive amounts of information are indispensable for unified consciousness > although the two hemispheres are completely insulated from each other, the brain as a whole is still able to produce only one conscious agent Seems like a contradiction of the assumption that they are "completely insulated". Overall I'm pretty skeptical of the notion that the two sides have "virtually no" connectivity and are "completely insulated" from each other, because of a mere corpus collosotomy. Does anyone else find this to be strange? Edit: According to another comment "anterior commissure and posterior commissure" regions can still communicate some signal.
- Sniffnoy 10y agoThis is an interesting experiment, and it may show that "split consciousness" is a mistake, but I don't think "unified consciousness" is the correct conclusion from that. I'd say instead that more likely this is just an edge case where the "consciousness" abstraction breaks down; it's an idea based on people who haven't had their corpus callosum severed, there's not necessarily any reason to expect that it continues to make sense in more general cases. Counting "How many conscious observers are there?" is probably just the wrong question.
- phkahler 10y agoFrom TFA: According to Pinto, the results present clear evidence for unity of consciousness in split-brain patients. I only read it as unified awareness, not consciousness. I recall reading that some split people were asked questions about their aspirations and got different answers depending which side of the brain they asked (you can ask by restricting input to half the visual field, or one ear or whatever, the response can be in writing). Having different goals in life seems more like consciousness than being aware of the location of some stimulus.
- insickness 10y agoA few years before he died, I heard Kim Peek speak at an event. He was a savant who retained 98% of everything he read. He would memorize phone books simply by reading them once. When he read, his left eye would read the left page while his right eye would read the right page at the same time. He could tell anyone the sports scores listed in the newspaper on the day they were born. He was also severely socially impaired and couldn't carry on a conversation. His father described his condition as being due to having his left and right hemisphere fused together where as most people's are separate with communication channels between them.
- YeGoblynQueenne 10y agoMy problem with that sort of demonstration of amazing memory powers is that I have no way to check the sports scores on the day I was born as quickly as the person who says they're retrieving them from memory does so. Even if I could just google them (there might be some online sports results archive or something- it would still not mean much unless I could find an identical copy of the exact listing the mnemonist memorised- like, a archived copy of the same newspaper they read on my birthday. So, I don't know- is this really a thing that happens even under at least semi-rigorous testing? Or is it more like a parlour trick that's only good for entertainment value?
- andrepd 10y agoWhat do you mean? You can't check the sports result he recalls on the Internet? What do you mean it has to be the same newspaper he read? I'm confused.
- Omnius 10y agoThe outcomes of historical, national, sporting events are not subjective. It would be easy to check and verify even if you couldn't do it that second you could still after the fact check and call out anyone pretending. With or without the exact identical text the "memorizer" used.
- YeGoblynQueenne 10y ago
- danbruc 10y agoThis seems weird. Assuming each hemisphere only receives information from one half of the field of view and only controls one half of the body and both halves are truly separated, than there is no [obvious] way both halves can act in a synchronized manner. At least one of the three assumption has to be false.
- mehwoot 10y agoand both halves are truly separated They aren't, they are just mostly separated
- 4bpp 10y agoNote though that this is n=2, and I'd assume the two subjects were not sampled even remotely randomly from the set of split-brain patients...
- ajkjk 10y agoWell, no, but with things like this you sort of tend to assume that the basic structure of everyone's brain is pretty much the same, so it only takes n=1 to stuff that you can pretty safely extrapolate to everyone. It would be a different matter if we expected an array of different brain mechanisms at the information-pathway level. Compare to how we do probably expect variation at, like, reasoning and emotional levels, maybe.
- throwaway26960 10y agoDoes every animal/insect have two brain hemispheres? For example, what about a spider, or an octopus?
- desireco42 10y agoExcellent question... does anyone know?
- aurelian15 10y agoWithout being an expert on the topic, I think it is safe to say that some symmetry in the nervous system is present throughout the entire animal kingdom -- just as bodies tend to be symmetric. For insects in particular, the brain is definitively split into two clearly distinguishable halves. Octopuses in particular are a completely different story, they don't seem to possess a "central processing unit", but rather distribute necessary computations throughout their entire nervous system (it is kind of fascinating). Yet, since they have two eyes, you'll still find two symmetrical nuclei for processing visual information somewhere in the vicinity of the sensor system.
- c3534l 10y agoSpiders have donut shaped brains. Source: owned a tarantula. Some animals jon't have bilaterally symmetric brains on account of having brains, like jelly fish.
- throwawayish 10y agoI remember an article saying that esp. in smaller spiders (so probably not tarantulas) the "brain" doesn't really have a simple shape, extending even into the limbs.
- c3534l 10y agoThat's also true for tarantulas. Their nervous system is fairly decentralized, but there's still a noticeable mass in their heads which is oddly shaped.
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- tempestn 10y agoIs it possible there's some wireless communication going on via electric fields that we're not yet aware of? Quick google search suggests this is a thing: https://www.sciencedaily.com/releases/2011/02/110202132617.htm https://www.sciencedaily.com/releases/2011/02/110202132617.h... Could it be happening on a large enough scale to allow communication between hemispheres though? I'm not suggesting this would take over for the corpus callosum, but rather that it may be happening for everyone, so the true amount of transfer even after the corpus callosotomy is higher than expected?
- throwawayish 10y ago> The green plasma... is a neurobinder! It allows instantaneous melding of connected minds over any distance.
- abalone 10y agoSo let's say there's some technology for creating a clone of you, complete with memories, an exact copy. You undergo the procedure and the clone is staring at flowers while you are looking at your shoes. Two questions: 1. What do you see when you swap your brain with the clone? 2. What do you see when you swap half your brain with the clone? My take is if we assume the brain is the seat of consciousness, the answer to 1 is flowers. But the answer to 2 is actually unknowable without experiencing it yourself. So, while it is interesting to discover that disconnected hemispheres can somehow learn to operate independently, we should be careful to note the empirical limitations of determining "unified consciousness". We simply don't know what the experience of consciousness is like in split brain patients, anymore than we'd know it in a clone with half your brain transplanted. We only know that they profess to feel no difference -- as undoubtably you and your clone would as well post-transplant.
- xg15 10y agoNot a neuroscientist here, so this is just layman's rambling thoughts, but I wonder if that much direct communication between the brain hemispheres were actually needed to appear as a single consciousness: As I understand it, a large part of how the brain develops is "learning" both about the environment and about the intricacies of one's own body. There is no engineer who calibrates the brain to work with the particular weight distribution of one's arms or the particular optical properties of one's eyes. Instead, the brain "self-calibrates" through a sort of trial-and-error process (and some deep learning magic I imagine). The two brain hemispheres are still sitting in the same skull for the entirety of one's lifetime - so even if they were not connected at all, they are still subject to the same environmental stimuli and might come to very similar "calibrations". So the appearance of a unified consciousness might come from the two hemispheres "thinking the same way", while also being subjected to the same stimuli.
- alok-g 10y agoHow would you apply the same reasoning to conjoined twins?
- delegate 10y agoA study of consciousness which doesn't include psychedelics is very limited. Studying consciousness by looking at the brain is like trying to figure out where a car goes by studying the mechanics of the car. Yes, the car moves because the engine transmits power to the wheels and makes them spin, ..., but that's just 50% of the answer. The other (true) reason it moves is because the human driver wants to get from A to B. So just ask the driver ! Of course that would require accommodating the idea that there is a driver - something outside the brain which is part of consciousness, which quickly leads to the study of what exactly is outside and inside and so on. Lots of answers and even more useful questions can be extracted from the study of psychedelics. Luckily I've seen that the ice has started to melt and more and more studies are underway, so we're going to see major breakthroughs in the field this century.