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Seperated brain hemispheres

  1. Jan 2, 2015 #1
    I was reading about alien hand syndrome about an hour ago, something peaked my interest. When where a person has had the two hemispheres of the brain seperated it leaves them susceptible to this condition, and from what I understand it's when the other hemisphere, the non dominant one, gains control of.. well your arm for instance.

    so I have to wonder something, if the dominant hemisphere is open to experience alien hand syndrome due to what is going on in the other hemisphere, does the other hemisphere function as a person and experience 'alien entire body' syndrome?

    Also, when you get a hemispherectomy, or have a large portion of your brain removed... doesn't the organ require some kind of support? and should you refrain from head banging? Because it seems liek there's a lot of free space, a vast open cavity for a less stable physical structure to move around and tear itself up in. Just an aside question. It seems like taking out a large portion of it without supporting it would make it less "structurally stable". Dunno, can't find an answer for this question specifically.
  2. jcsd
  3. Jan 2, 2015 #2


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    Please post links to the research to which you are referring. Thanks.
  4. Jan 3, 2015 #3


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    Firstly, you have two questions here. I suggest you delete the second question from your OP and make a second thread to keep the topics distinct and focused. A brief review of alien hand syndrome can be found here:


    It's an interesting question. Here's the difficulty with your proposition. Those activated sections of the motor cortex are dedicated to running muscle programs given a particular stimuli (muscle programs that are designed/learned as you learn to do new motor tasks). So the actions of the alien hand could simply be automatic responses running independently of any conscious focus.

    from the alien syndrome review paper:
    and from a neuroscience textbook:

    (University of Texas electronic Neuroscience textbook)

    The authors of the first paper say in the discussion:

    Last edited: Jan 3, 2015
  5. Jan 3, 2015 #4
    First, here's a link that describes what can be meant by "Alien Hand Syndrome":

    In the case of patient "Paul S.", both of his brain hemispheres had some language ability. So when the calloscotomy was performed, it was possible to directly inquire about possible differences in their opinions and perceptions. I do not have access to the original papers from Nobel-laureate Roger Sperry, but here is a popular article based on some of that work:

    From this, you might think that one hemisphere could independently suffer "alien entire body syndrome". But remember that these studies are done on patients with a massive communications circuit completely severed. The corpus callosum consists of more than 200 million axons. With such a massive communication link, one would expect that whatever thoughts cross one half of the mind are well considered by the other half.
  6. Jan 3, 2015 #5
    A simple test to address this question is simply to ask the non-dominant hemisphere whether it experiences 'alien entire body' syndrome. If you don't get an answer, which you typically don't, then the answer to that question is no. We typically define terms such as "experience," "consciousness," "first-person awareness," etc. as the instrospective report of some qualitative sensory or cognitive event which most often can be communicated to other individuals as such an experience verbally. An alien hand picking up a glass of water and pouring it on someone's head does not qualify as such an introspective report. Designating a condition as an "alien" hand syndrome implies that there is no communicable first-person knowledge or awareness of what that hand is about to do or why it's going to do it. Subsequently, we can infer that it has no first-person awareness of what the contralateral half of the body is doing.
  7. Jan 3, 2015 #6


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    Playing devil's advocate here, since "entire body" (besides the arm/hand) would include ears and tongue, it would be difficult to interact with the dissociated hemisphere; asking the question and not getting an answer wouldn't tell you anything about the dissociated hemisphere, since you'd be asking the associated hemisphere.
  8. Jan 3, 2015 #7
    It's not so simple. I can't find any freely available papers about Paul S from Roger Sperry himself. But if you Google "Paul S split brain" you will find numerous excerpts from his work. The problem is that in almost all cases (patient Paul S. being the exception), the right hemisphere does not have enough language skill to express any sense of consciousness or being. Asking it about "entire body syndrome" would be way beyond its abilities to either understand or respond to.

    BTW, if anyone can find a freely published copy of the work by Roger Sperry that won him the Nobel prize, please post a link. Thanks.
  9. Jan 4, 2015 #8
    That is correct, as confirmed by the Wada test:


    A person's non-dominant hemisphere will not even be able to understand what you are saying. It will sound like gibberish to them.
  10. Jan 4, 2015 #9
    Well, that's kind of my point. If the person or organism is not able to give an introspective report of their experience, then ascribing a measure of "human-like" consciousness or agency to that entity is entirely a matter of conjecture. You could make the same argument that a nonhuman species such as a groundhog or a Salamander has an introspective awareness of what body parts belong to "itself" and which are alien, only we can't know this because they don't have the vocal equipment to convey that.

    In the same way, just because a split brain patient's nondominant hemisphere can pick an object out of a bag without being able to report what it is, doesn't necessarily mean that this person possesses two separate "selves" per se. The null hypothesis is that they don't without dual introspective reports, as I stated above.

    "Michael Gazzaniga, a cognitive neuroscientist at the University of California, Santa Barbara, and the godfather of modern split-brain science, says that even after working with these patients for five decades, he still finds it thrilling to observe the disconnection effects first-hand. “You see a split-brain patient just doing a standard thing — you show him an image and he can't say what it is. But he can pull that same object out of a grab-bag,” Gazzaniga says. “Your heart just races!”"
  11. Jan 4, 2015 #10
    If the non-dominant hemisphere has no language abilities then the next best test for consciousness or agency is certainly something like showing them an object and seeing if they can pick the same object from a bag.

    You ought to read "My Stroke of Insight" by Jill Taylor. Her language abilities were destroyed by a brain bleed and it took eight years for her to recover. Having regained language she was able to describe what life was like without it.

    I also suggest "Seeing Voices" by Oliver Sacks, which is about the world of the deaf. Historically, deaf people went through life without language because modern, organized sign language is a relatively recent development. They were in a boat not at all unlike people who've had their language centers destroyed. They wouldn't be able to report any experience, but I think it would be ridiculous to suppose they had no experiences.
  12. Jan 4, 2015 #11
    FWIW, when we are discussing reporting awareness we are describing a conscious organism. The only biologically motivated complete theory (predicts both "when" and "how") I know of is recent, Graziano's toolkit of the two putative brain centers making us aware of awareness.

    "In Graziano's attention schema theory, awareness is the brain's simplified model of the complicated process of attention. When a person is aware of something such as an apple in front of them, it is because the brain has put together two models: the information describing the apple, and the self-descriptive information about how the brain is focusing its resources. Put those two specialized types of information together and the brain is equipped to introspect, conclude and report, "I am aware of the apple."

    The attention schema theory satisfies two problems of understanding consciousness, said Aaron Schurger, a senior researcher of cognitive neuroscience at the Brain Mind Institute at the École Polytechnique Fédérale de Lausanne in Switzerland who received his doctorate from Princeton in 2009. The "easy" problem relates to correlating brain activity with the presence and absence of consciousness, he said. The "hard" problem has been to determine how consciousness comes about in the first place. Essentially all existing theories of consciousness have addressed only the easy problem. Graziano shows that the solution to the hard problem might be that the brain describes some of the information that it is actively processing as conscious because that is a useful description of its own process of attention, Schurger said.

    "Michael's theory explains the connection between attention and consciousness in a very elegant and compelling way," Schurger said.

    "His theory is the first theory that I know of to take both the easy and the hard problems head on," he said. "That is a gaping hole in all other modern theories, and it is deftly plugged by Michael's theory. Even if you think his theory is wrong, his theory reminds us that any theory that avoids the hard problem has almost certainly missed the mark, because a plausible solution—his theory—exists that does not appeal to magic or mysterious, as-yet-unexplained phenomena."

    [ http://medicalxpress.com/news/2014-01-toolkit-human-consciousness.html ]

    Note though that it isn't yet much tested.

    Re the animal discussion: Since I am interested in astrobiology, I wanted to ask how far back we can see homologies to these two brain areas that bridge the parietal and temporal lobes.

    They do have homologies in earlier hominids according to fossil brain case imprints, but there were also a larger reorganization of the brain around when Homo first appeared it seems. So one can argue that it is a late evolutionary trait, or that it appears in apes or monkeys or possibly earlier. Since being aware of awareness would be a useful trait in the generic prey/predator interaction (as in don't eat without watching out for predators, say) and seems simple enough to evolve, consciousness could be very old. Perhaps we can find out, if we can bypass the language requirement (or ask parrots what they look at and see how homologous areas, if they are there, behave).
    Last edited: Jan 4, 2015
  13. Jan 4, 2015 #12
    If you're talking about hemispheric asymmetry, it is a decidedly unique human trait, notwithstanding some ambiguous handedness studies in extant primates.

    When you make statements like this, you need to clearly define what you mean by "consciousness," and the distinction between human consciousness and non-human consciousness, if you believe there is one. Plus, if you're going to make an assertion that "awareness of awareness" is a simple feature to evolve, please expand upon that argument and tell us how this simple feature of self-awareness/consciousness is manifested in neural tissue.
  14. Jan 4, 2015 #13


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    If you mean this statement in general, it's not quite the case. Several species of crustacean have nervous system assymetries associated with their larger and smaller claws (precision vs. strength), while many birds have hemispheric asymmetries (you might notice chickens always have one eye on the ground - a typical bird hemispheric assymetry is to have one way for detail-focused search tasks aimed at finding food on the ground, the other more of a general motion sensor aimed at the sky.) The following review on assymetry discusses it in birds, worms, zebrafish, crabs, and flies. Some of these animals have hemispheres, others do not, but assymetry in the nervous system is an old trait.

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  15. Jan 5, 2015 #14
    I did not mean that as a general statement referring to the entire animal kingdom, I meant it for mammals in general and primates in particular, because Torbjorn_L was referring to the temporo-parietal junction, which is an isocortical feature.

    The species you mention here are not even in class mammalia so I don't think it's relevant to this particular issue. Between the time of the common ancestor of apes and humans to the present, the mammalian/primate brain has undergone an unprecedented and discontinuous specialization of cortical laterality, which is conspicuous and henceforth highly relevant in questions regarding the evolution of human cognition and consciousness.

    From: http://www.ncbi.nlm.nih.gov/pubmed/23631481

    "We conclude that the robust, species-wide lateralization that exists in humans is unusual, and perhaps unique among primates, and discuss several possible evolutionary explanations for this strong asymmetry."

    From: http://www.ncbi.nlm.nih.gov/pubmed/23529256

    "Over the last two million years, the brains of our more recent ancestors increased greatly in size, especially in the prefrontal, posterior parietal, lateral temporal, and insular regions. Specialization of the two cerebral hemispheres for related, but different functions became pronounced, and language and other impressive cognitive abilities emerged."
  16. Jan 5, 2015 #15
    Wow, from that 2nd link: " As a consequence of this complete split, Peek, who sadly died last year, was able to simultaneously read both pages of an open book and retain the information. He apparently had developed language areas in both hemispheres. ". This patient still had some of the connections between the hemispheres intact though. When they're isolated, you'd expect that you'd have 2 different persons yes, but with not that much different personality, because an hemispherectomy doesn't drastically change personality. Since the hand is the only way of that hemisphere to communicate, that would explain that syndrome - you wouldn't want to pass all day without moving a muscle, moreover with no sight or hearing. It's a bit barbaric to keep that hemisphere alive, because it's like being a person who can't see, hear anything or communicate, just being able to move its hand, and with no way of deciding its faith. I'd expect it to move rapidly to a mental illness given all of the senses deprivation, although this is just speculation.
  17. Jan 6, 2015 #16
    I'm pretty sure the non-dominant hemisphere can see and hear just as well as the dominant after severing the CC, however well that is.

    Perceptions, however, may be altered in ways we wouldn't anticipate. Jill Taylor reported an inability to separate a thing from the surroundings unless it moved. Her environment seemed to her to be a monocoque entity, and she would lose awareness of even people as autonomous beings in that environment, until they moved. I have no idea what that would be like, but from her descriptions it seems like it was more of an interpretive deficit than anything else. She could see separate features of her environment, but she didn't interpret them as separate things. This suggests the dominant hemisphere performs a lot of discriminatory functions we don't even realize need performing until the ability to do so is impaired.

    In any event, I agree with you that separating the hemispheres leaves the non-dominant hemisphere bewildered in a world it can't make sense of. I would not be surprised if it sometimes deliberately did contrary things to express itself.
  18. Jan 8, 2015 #17
    I am not. Maybe Graziano is.

    As I already commented, one can argue that it is a late evolutionary trait (after developmental differences appears), or that it appears in apes or monkeys or possibly earlier.

    That doesn't pass the smell test:

    'When you make statements like this, you need to clearly define what you mean by "sexuality," and the distinction between human sexuality and non-human sexuality, if you believe there is one.'

    The definition is in Graziano's papers.

    It is simple compared with evolution of vision, say, no new receptors and/or actuators. In fact, since neural tissue is interconnected I didn't think much on the issue. Maybe I should revert that to say that there is no evidence that suggests it is harder to evolve than other behavioral traits. (So those that want to see consciousness as something special have to motivate that.)

    Again, that manifestation is in Graziano's paper.
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