Does Split Brain Surgery Show There Is No Soul?

Cerebral_lobesI’ve been recently reading up on split brain surgery, and how it effects behavior. What made me originally curious was Sam Harris’ newest book, Waking Up: A Guide to Spirituality Without Religion.

In that book, Sam Harris talks about consciousness and what makes us who we are. He describes (paraphrasing) how we feel as if we’re something riding around in our heads and looking through our eyes. He explains what consciousness is

 “an experiential internal qualitative dimension to any physical system.” Put more simply, consciousness is what it’s like and how it feels to be you.

He then goes on to talk about the ego or the sense of ‘I’ that we experience as human beings:

“The sense of being an ego, an I, a thinker of thoughts in addition to the thoughts. An experiencer in addition to the experience. The sense that we all have of riding around inside our heads as a kind of a passenger in the vehicle of the body…. Now that sense of being a subject, a locus of consciousness inside the head is an illusion. It makes no neuro-anatomical sense. There’s no place in the brain for your ego to be hiding.”

Later he talks about a medical procedure called calloscotomy, which inhibits the right hemisphere from communicating with the left. They have done this procedure to people who suffer from severe epileptic seizures.  They’ve also performed this procedure on various animals, including cats and monkeys.

So here’s the really interesting part. In my opinion anyways – when they do this procedure, it’s as if they create two consciousnesses in one skull. It’s creepy but it’s almost as if two people are sharing the same body.

In one test, they showed a subject who had undergone this procedure a set of four different colored blocks. Then they showed him a picture of the blocks in some arrangement in front of him and asked him to duplicate it with his blocks. The subjects right hand (the left hemisphere controls the right side as well as visual-motor capacity) was easily able to complete the task, but the left hand (controlled by the right hemisphere) could not.

However, it gets even stranger:

But more surprising was this: As the right hand kept trying to get the blocks to match up to the picture, the more capable left hand would creep over to the right hand to intervene, as if it realized how incompetent the right hand was. This occurred so frequently that Gazzaniga eventually asked Jenkins to sit on his left hand so it wouldn’t butt in.

When Gazzaniga let Jenkins use both hands to solve the problem in another trial, he again saw the two brain hemispheres at odds with one another. “One hand tried to undo the accomplishments of the other,” he wrote. “The left hand would make a move to get things correct and the right hand would undo the gain. It looked like two separate mental systems were struggling for their view of the world.”

The take away from this experiment and many more that they’ve done since is this:

“The demonstration that you could in effect split consciousness by splitting anatomy—by just making a tiny change in anatomy … It was one of the most remarkable results in neuroscience, with huge implications,” said Patricia Churchland, a philosopher at the University of California, San Diego, whose work focuses on the relationship between philosophy and neuroscience. “If you thought that consciousness and mental states were independent of the brain, then this should have been a real wake-up call.”

Helping to illuminate the relationship between the mind and the brain, according to the cognitive psychologist Steven Pinker, is one of split-brain research’s most important contributions to modern psychology and neuroscience. “The fact that each hemisphere supports its own coherent, conscious stream of thought highlights that consciousness is a product of brain activity,” he told me. “The notion that there is a single entity called consciousness, without components or parts, is false.”

We have often described our ‘self’ as something separate from our bodies. Most of our religions describe some sort of soul that leaves or changes as we die, but this experiment shows that by simply cutting off communication between our two hemispheres, we can create two consciousnesses that are independent of one another.

While you’re reading this, you could have two different opinions of this piece, depending on which hemisphere you asked.

How creepy but fascinating is that? And are there more ‘I’s’ lurking around in our skulls that we haven’t discovered yet?

No matter how you look at it, I think this shows that the soul doesn’t exist if you think your consciousness or the thing that you describe as ‘I’ or ‘you’ is essentially what your soul is.

What do you think?



  1. Actually, Victoria Neuronotes has linked a video on her blog and elsewhere about a doctor talking about a person who had the procedure done. The man actually had a theist half of his brain and an atheist half. It was wondered aloud whether only half his brain would get to heaven.

  2. Brain injuries also put a big hole in the soul hypothesis. It is said that our soul contains all that makes us who we are—our personality at its core. Yet, if we bonk our head hard enough, our whole personality can change. How anyone can keep pretending that our consciousness is somehow metaphysical is beyond me.

    It does bring up an interesting issue, though. If we are wired to be more likely to either believe or not, does that mean that there are people who could literally never be atheists or vice versa (barring surgery or injury)?

    • To me, it’s often described much like a God, except without the super powers. I don’t get the whole ‘it can feel, think, live’ without a physical body. We see no examples of that anywhere else in nature, unless you credit ghost stories, which I don’t. I find them fascinating but not convincing.

      If there is a soul it must serve a function and I just don’t see where that function would come from. The consciousness seems to be the last hiding spot for such a thing.

  3. I think we don’t know enough about the brain yet. Can the two sides ever communicate if separated? Maybe. That’s a whole other study and post 🙂 But I don’t believe there is a soul in there. I do believe consciousness resides in the brain, but that means it is also dependent on the brain’s vulnerability. So what could that even mean spiritually?

    My husband had a significant portion of his right temporal lobe removed in 2007. It has affected him in the strangest ways, but overall he is the same person. The surgery process is fascinating when it’s controlled and mapped out ahead of time. They could turn off parts of his brain and ask him questions to see how well he would function- but they cannot know how the brain will react long term. It finds new pathways, which does change a person in unpredictable ways.

    When people suffer great damage from injury or illness, Christians claim that they will be restored in heaven. I have always wondered where the restoration cutoff falls. Will my husband be restored to where his brain was before? If we have souls, do they just hold onto the most ideal version of us until we die, or what? None of this makes sense. Maybe that’s why I don’t believe it.

    • Neuroscience is so interesting. For such a small organ, our brain does so much, and even more that we don’t yet understand.

      “I do believe consciousness resides in the brain, but that means it is also dependent on the brain’s vulnerability. So what could that even mean spiritually?”

      I’m still in the beginning of Sam’s book but I hope to do a review later, after I’ve read his answer to that question. I really want to know what he means by spirituality and what it means to the brain.

      “My husband had a significant portion of his right temporal lobe removed in 2007. It has affected him in the strangest ways, but overall he is the same person.”

      Wow. That must have been scary for him.

      Even with split brain, people didn’t seem much different at first. Only when scientists started looking closer did they notice how different they were.

      “Will my husband be restored to where his brain was before? If we have souls, do they just hold onto the most ideal version of us until we die, or what? None of this makes sense. Maybe that’s why I don’t believe it.”

      Good questions and I fall on the same side as you – I don’t believe them and I don’t think we have souls. Just a brain.

  4. Pingback: Does Split Brain Surgery Show There Is No Soul? | Those of Rose

  5. Fantastic post, GC. Right up my alley. 😉 Here’s something else to think about — when the brain is injured or damaged in specific areas, the person changes, sometimes into a completely different personality. When you have time, I highly recommend this lecture by Neuroscientist, David Eagleman. It’s well worth the time invested. He discusses consciousness as well.

    I saw my late husband’s personality change dramatically after he sustained a traumatic brain injury to the left temporal lobe. He became a completely different person. Traumatic brain injuries occur approximately every 15 seconds in America according to the Brain Injury Association of America.

    Based on over 10 years of independent research, I do not think there’s such a thing as a soul, and the split-brain experiments aren’t the only examples of why I’ve come to that conclusion.

  6. Pingback: Is this proof the soul does not exist? | Eirene Hogan

  7. The Triune God must have a brain with three parts, and we are all Diune Humans. Post-hoc rationalization coming soon to an apologist near you 😏

    I wonder if I only think I’m one person because my two halves have a conversation and come up with one story before doing anything. I am they, so they think they are one person.

    A story about a deity with an infinite number of brain spheres would be interesting. Or perhaps a deity that is Omnisphere. We are all it but don’t know!

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