Split Brain, One Consciousness

Discussion in 'Human Science' started by Bowser, Feb 27, 2011.

  1. Bowser

    Bowser Life is Fatal.

    Reading a page tonight, I discovered something interesting about the nature of consciousness. It seems that people who have had split brain surgery do not experience two separate consciousnesses, even though their two halves appear to be working independently of each other.


    According to the above, it would seem that consciousness is seated in the left hemisphere of the brain near the speech center. However, this doesn't appear to be the case when a hemispherectomy is performed on the left hemisphere, which would suggest that consciousness is migratory within the brain.

  2. jmpet

    jmpet Valued Senior Member

  3. Stoniphi

    Stoniphi obscurely fossiliferous

    As I recall it, consciousness usually starts out seated in the right hemisphere then migrates to the left hemisphere as we age. This can be noted as our emotions become less angry and hostile due to the increasing influence of the left amygdala which seats the more positive emotions and the lessening influence of the right amygdala.
  4. Billy T

    Billy T Please use Sugar Cane Alcohol Fuel

    IMHO, most of this conclusion is due to an over identification of "consciousness" with internal speech (or verbalized speech that honestly reflect the thoughts of the internal /silent speech). Daniel Dennett’s book Consciousness Explained being an extreme case of the very questionable identification between {internal} speech and consciousness.

    There are many cases where speech is lost* due to strokes, yet consciousness clearly is not. When a left hemispherectomy is done, "consciousness definitely" does not "migrate" - only an ability is lost and it may be learned by the right hemisphere, especially in the very young when learning and plastic brains are normal.

    At JHU hospital many years ago, when I had some connections with a couple the neurosurgeons, there was a young (< 2 years old, as I recall) girl with Status Epilepsies who had one hemisphere (the left as I recall) removed. When she was older (say 10) she was essentially normal - only careful testing reveled her defects.

    SUMMARY: This view that consciousness = internal speech only reflects how little man understands what is consciousness or how it is achieved.

    * If stroke is in Wernicke's area, then speech comprehension is mostly lost and the produced speech is "fluent word salad." If stroke is in Broca's area, then there is no more loss of speech than if the tongue were cut out. I.e. full comprehension, and internal speech is preserved, but the necessary motor coordination to produce speech is lost. In neither case is "consciousness lost" - only communication abilities (extreme for a Wernicke stroke) are lost.
    Last edited: Feb 27, 2011
  5. Bowser

    Bowser Life is Fatal.

    But that would leave a person with out consciousness who has had their left hemisphere removed.
  6. Bowser

    Bowser Life is Fatal.

  7. Stoniphi

    Stoniphi obscurely fossiliferous

    The pivotal word is "seat". Persons who lack 1/2 of their brain situate their consciousness in the remaining portion.

    Occam's Razor - parsimony would indicate there is no need for 2 seats of consciousness so it most likely won't happen.
  8. Billy T

    Billy T Please use Sugar Cane Alcohol Fuel

    If consciousness is more related to qualia, as I think it is when contrasted to awareness or the internal speech then split brain individuals often do have split consciousness. - For exmple it is possible to show different scenes (or even different movies) to each brain half. One can evoke the qualia of anger in one half brain and the other sadness. etc. I.e. how we are feeling, what were are experiencing emotionally, can be different for each half.

    One also see some thing like this in the alien hand syndrome - one hand under conscious control will grasp the other "alien hand" to prevent it from some inappropriate action, etc.
  9. Billy T

    Billy T Please use Sugar Cane Alcohol Fuel

    Much of your links results were know long ago in "dicottic listening" experiments where one attends to / is conscious of / the audio presented to one ear, yet the meaning of ambigious terms in that attended audio stream is strongly controlled by their presence in the stream you are not conscious of if context there makes their meaning clear.

    This of course did not tell anything about what part of the brain was being used -only that both stream were processed to a high level. The brain does many things and consciousness is only informed of a few.
  10. drumbeat

    drumbeat Registered Senior Member

    It's like 2 separate brains, but the final decision is down to the left-side.

    Some people have had damaged brains that has left them with both sides with equal influence, and had such problems as 'Alien Hand Syndrome' where the left hand (controlled by the right brain) moves seemingly of its own accord.
  11. billvon

    billvon Valued Senior Member

    That's assuming that there is a discrete location for consciousness. I don't believe that there is. Is there one computer that is the Internet? Where is the Internet located? If you determine that one computer is the Internet, and you disconnect it, and the Internet continues to function (albeit with some impairment) - does that mean the Internet is migratory?

    Or is the function that the Internet performs scattered throughout all the parts of the network?

    Consciousness is almost certainly an emergent property of a complex neural network, and as such doesn't really have a "central location" of consciousness. It's not a part that can be isolated; it is a property of the system as a whole.
  12. Bowser

    Bowser Life is Fatal.

    I'm just following the path presented by the information available when starting this thread. I did, however, post a link in this thread to a page that would seem to support your theory. I ran into the page after starting this thread.

    The implication is that consciousness may still survive even in the most severe cases of brain damage.
  13. Twine

    Twine Registered Senior Member

    I don't think the quote you gave implies that consciousness is in the left hemisphere. It should be completely obvious that the speech center can't receive any information about your right brain being conscious of something. It could be possible that the right brain is conscious (meaning, experiences qualia) of certain things, but can never communicate this through speech.

    I'm curious as to what a split-brain patient would write with either hand if you asked them "Can you speak?"

    When the writer you quoted says
    he does *not* mean to say that your brain has one consciousness. What he is actually saying is that "the consciousness of the right hemisphere" is separate from the left, and that the left brain is not conscious of things experienced by the right brain. Of course, this should be obvious.

    That writer is not saying "people who have had split brain surgery do not experience two separate consciousnesses", but rather is saying "the left brain of people who have had split brain surgery does not experience two separate consciousnesses"
  14. Fraggle Rocker

    Fraggle Rocker Moderator

    Cetaceans obviously cannot "sleep" the way other mammals do or they might drown. So they have evolved the unique ability for each hemisphere to sleep independently while the other takes care of business. I wonder what goes on when the sleeping hemisphere wakes up. Do they have a meeting to catch up on the news?
  15. Billy T

    Billy T Please use Sugar Cane Alcohol Fuel

    Sharks must swim to breath (force water thur slits that unlike fish can not move gill flaps to pump it thru) They too sleep each half of the brain separately so they can swim from birth until death.
  16. Fraggle Rocker

    Fraggle Rocker Moderator

    I didn't know that fish, much less the primitive cartilaginous fish, sleep. They have such tiny forebrains, I didn't realize it was divided into hemispheres. What does that make, about eighty-five brain cells on each side? :) So then do all chordates sleep? Seems like a real disadvantage in that environment unless you're the apex predator.
  17. Billy T

    Billy T Please use Sugar Cane Alcohol Fuel

    Yes fish sleep. It may not be identical to our sleep with different sleep states. E.g. there is little or no evidence to suggest REM sleep* in fish, but when you think about it REM sleep is detected by the electrical artifacts associated with mussels moving the eyes. Fish at least as a general rule don’t move their eyes much so there electrical REM signals, if existing, would be small and hard to detect.

    ““Researchers have now been able to show not only that [zebra] fish sleep, but that they can suffer from sleep deprivation and insomnia. By repeatedly disturbing the fish using mild electric shocks, researchers were able to keep zebra fish awake at night. Those fish that had suffered a disturbed night were found to catch up on their sleep as soon as the opportunity arose.”” From http://bigquestion.wordpress.com/2008/03/04/how-do-fish-sleep/

    Also see:

    Having a tiny brain would not seem to me to make it more difficult to sleep – perhaps easier? Bats certainly sleep (and upside down at that) and their brains must be smaller than a shark’s.

    *I don’t know but strongly suspect that normal REM sleep is absent in congenitally bind humans too. They may move their unseeing eyes, but not as in normal REM sleep. What would be interesting to know is how these periods of movement are distributed during the night. For example in concentrated intervals that are more common before waking up? I am almost sure congenitally bind humans do dream, but their dreams must be more tactile etc. than a sighted human’s dreams.

    PS I learned about shark sleep years ago. As I recall, the researcher did have micro electrodes into each side of their brain. (And presumably a strapped on recording system - I don't recall.)
  18. billvon

    billvon Valued Senior Member

    So? We must breathe each minute or so to live, and yet we sleep for 8 hours at a time. We don't need to "sleep each half of our brain" so we can keep breathing. Automating breathing isn't much different than automating swimming.
  19. Billy T

    Billy T Please use Sugar Cane Alcohol Fuel

    So you say, but I will stick with the known facts -sharks sleep half the brain as swimming is not that automatic - perhaps so they don't try to swim upon the beach or into a boat? Also swimming takes considerable energy so when doing it, finding food or a mate etc. with no more energy is well combined with just breathing from an energy POV.
  20. chimpkin

    chimpkin C'mon, get happy!

    Yeah, but you can be in a vegetative state-lose higher function, and the brainstem will still keep you breathing if it's working okay.

    I think what the sharks do would be more like those people who get in the car and sleep-drive on Ambien or something.

    I think bats are smarter than sharks...sharks are pretty dumb.

    Hmm, I wonder if there's been any cases of Dissociative-Identity people having major head injury and losing someone in there?
    Just a thought.

    I don't know that I experience myself as...entirely unitary? or maybe it's just really noisy in here...but there is sort of a me and a not-me that is also me and the conversations get spoken aloud in many instances.

    I also don't feel like I'm the same person that I was 20 years ago, I just happen to share exact history with that person. If I have a personal "growth spurt" I could be a different person again in a year or two.
    Last edited: Mar 1, 2011

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