Split-brain patients and the dire implications for the soul

Note: I have changed the title of this post for the benefit of readers who are unfamiliar with the term ‘substance dualism’.

Many of our readers – especially among the regulars at Uncommon Descent – are substance dualists.  That is, they believe that each of us has an immaterial mind or soul that constitutes our true self, and that the body, including the brain, is merely a vehicle “inhabited” and controlled by the mind or soul.

There are many problems with this idea, which is why it is rejected by most neuroscientists and philosophers.  One of the most striking is the problem posed by the strange characteristics of split-brain patients, as described in this video by VS Ramachandran:


Not only do the separate hemispheres exhibit distinct personalities and beliefs, as Ramachandran explains; they even have separate wills.  I described this in a comment at UD a few years ago:

Even stronger evidence against the dualist position is provided by split-brain patients. There is a procedure, the corpus callosotomy, that disconnects the two hemispheres so that epileptic seizures cannot spread from one to the other. The hemispheres are only disconnected; neither is removed. This operation contains the seizures, dramatically improving the patient’s quality of life, but it also severs the path through which the hemispheres normally communicate. The results are fascinating, and they’re not very friendly to the dualist position:

a. In experiments with split-brain patients, it’s possible to pass information to one hemisphere but not the other. The left hemisphere literally doesn’t know what the right hemisphere knows, and vice-versa.

If there were a single, immaterial mind, it would know what both hemispheres know. Clearly, this doesn’t happen. As a dualist, how do you explain this? Surely the immaterial mind doesn’t split in two at the moment the corpus callosum is cut, does it?

These fascinating videos of a split-brain patient demonstrate the phenomenon:

video 1

video 2

b. The left hemisphere controls the right half of the body, and vice-versa. When the connection between the two is cut, this results in bizarre behaviors indicating the presence of two “wills” in the same skull.

One patient was seen to pick up a cigarette with her right hand and place it in her mouth. Her left hand plucked it out and threw it away before the right hand could light it.

In another case, a man attacked his wife with one arm while defending her with the other.

If a single immaterial mind were running the show, this would not happen. How do you explain this within the dualist framework?

The question is just as relevant now as it was then.  Dualists, how do you reconcile these phenomena with your worldview without twisting yourselves into logical pretzels?

114 thoughts on “Split-brain patients and the dire implications for the soul

  1. Sriskandarajah,

    Have you looked at the evidence I’ve provided in this thread?

    Rather than asking a lot of roundabout questions, it would be better if you would explain why the evidence I’ve presented doesn’t lead to the conclusion I draw.

  2. keiths:
    A lot of your comments end up getting posted twice.Do you know why that’s happening?

    A side effect of dualism.

  3. Keiths,

    Yes. I know my comments posted twice due my posting error. Sorry for that. But it has nothing to do with my questions.

  4. Sriskandarajah,

    The comment links on the front page are broken for this thread (it just happened today). To get to the latest comments, you have to to load the thread and then click on ‘Newer comments’ at the top or bottom.

    But if you’re able to read this comment, you’ve probably already figured that out. 🙂

  5. keiths:

    The comment links on the front page are broken for this thread (it just happened today).To get to the latest comments, you have to to load the thread and then click on ‘Newer comments’ at the top or bottom.

    But if you’re able to read this comment, you’ve probably already figured that out. :-)

    Seems to be a problem with fixed pages too. Have cleared the cache but it has made no difference. It might be something to do with the age of the thread, perhaps.
    Would a new thread make sense?

    PS Welcome Sriskandarajah.

    PPS. Has someone done the housekeeping? I don’t see any duplicate comments.

    ETA tried changing the date on the post to see if that changes anything but the comment links still don’t work 🙁

  6. This thread is defective. Links do not go to the end of the thread. I would like to see this last post moved to the start of a new thread that would link correctly.

  7. petrushka,

    I’ll start a new thread and ask the moderators to inform Sriskandarajah by email.

  8. I’ve moved some comments. The rest seem more about site mechanics than related to the topic of the thread. Not sure about emailing folks either.

  9. Keiths,

    Thank you for welcoming me.
    You all claim that there is no immaterial soul. Dr Ramachandran claims that there are two persons in a split brain. I do not claim any things.
    We need to depend on technological science, food science, biological science and medical science. These are all external. It is very difficult to make you understand something related to internal and subjective. Further you are deeply confined to the ideas of atheism and materialism. So you always try to see things in terms of atheism and materialism. Your internal world is only for you. Nobody can enter there. The Neurologists can study your external brain. They can’t see what is really going on internally. For an example they can explain all chemical and neurological process going on in your brain during the time you eat some sweet chocolates. But the sensation of taste is only for you. Many neurons are involved in a process to give you the taste sensation. You only enjoy the taste of sweetness. One side, there is brain with billions of neurons which is engaged in a process. Other side you enjoy the taste sensation. When I say this, please don’t think there is an entity inhabiting your physical body. That is the mistake you all do and say there is no immaterial soul. I am not talking about an immaterial soul here. I am talking about you. That is why I am asking the question what you are. At the time you enjoy taste sensation you are not aware of what is happening in your brain. Neuro scientists can study your brain and may write books on what is happening in your brain. They are unable to connect the external with the internal.
    Dr Ramachandran is only aware of the external part and makes concepts and conclusion about the internal part which he is not aware of. It is really absurd.
    Do you understand my question what you are? If you don’t understand my question then there is no point of answering your question. If you ask this question deeply into yourself inwardly after free yourself from all kind of beliefs then you will understand the fallacious split brain concepts.
    Neurologists say that there are two minds in a split brain. They say that there are two selves in a split brain. They say that there are two persons in a split brain. Before making those concepts they should understand what is mind, what is self, what is person and what consciousness is. They should understand what it means by mind, self, person and consciousness. To understand those things first we should understand what I am. Without knowing myself, I cannot understand those things. Dr Ramachandran identifies the beliefs as persons. Many neurologists like Dr Ramachandran mislead the people. They mix up all these terms which have different meanings and make all wrong statements. They don’t know how a sense of experience arises through the brain. They are unable to heal even a slight damage in the brain. But they make concepts about what is happening internally which they are not aware of.

    There are many activities going on unconsciously. A car is moving unconsciously. An aero plane is flying unconsciously. There is lightning and thundering without awareness. When the tail of a lizard is cut, the separated tail of a lizard makes movements. A severed lizard’s tail that keeps on twitching. Do you say that the tail makes movements consciously? We see in our self many unconscious functions. If you understand those unconscious functions in your existence you will see what Dr Ramachandran saying is false.
    You ask this question.
    Do you accept what Dr Ramachandran says about two persons in a split brain? You ask me “How you do know that? How can you tell, from the outside, that one of the hemispheres is unconscious?”
    Good question. I have already explained the falseness of the brain concept very clearly. It is not necessary for any further explanation. However, if you accept what Dr Ramachandran says, please explain the following questions.
    How does Dr Ramachandran know that? How can he tell from the outside that both split hemispheres are conscious?
    Your explanation answers to your question.
    If he determines the internal awareness of each hemispheres from what comes from the mouth of the split brain person then really that is false. Our memory is very powerful. It may release the contents unconsciously. Our brain can do many functions unconsciously. To know that you should be aware of yourself inwardly and you should understand the question what you are.


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