Consciousness: Through the Lens of Split Brain Experiments

Where are you? That thing that is the doer, where is that located?

Our brain is divided into to hemispheres, left and right. These hemispheres are connected through a bundle of nerve fibers called the corpus callosum. This structure allows for information exchange between the two halves of our brain. This, it turns out, is very important as the individual hemispheres of our brain complete separate tasks, then share the information with the other half. The specific tasks that are carried out by each hemisphere are conserved in most people. That is to say, there are some exceptions to these rules, but the work is typically divided the same way across different peoples. As a brief example of this, examine the figure below.

This list could be longer and more detailed, but the important distinctions are: each hemisphere receives different visual inputs, controls different sides of the body, and that speech and language are confined to the left hemisphere.

A treatment for the most severe and uncontrollable epilepsy is to cut the corpus callosum. This is a last line measure (no response to anti-seizure medication and other treatments) to limit the spread of the electrical activity of epileptic seizures. While cutting the corpus callosum did not completely stop the seizures, it relegated them to the half of the brain they originated in, no longer being able to spread to the other hemisphere via the corpus callosum. I will leave the ethics of this procedure for others to debate, but to the impartial observer, this procedure shed light on some peculiar aspects of consciousness.

Let’s walk down the logical progression of cutting the corpus callosum. No communication, no information exchange between the two hemispheres. Each hemisphere only receives visual input from one visual field. For those that are unaware, if you stare at a dot in the middle of the screen, images to the left of that dot are located in your left visual field, and vice versa. Therefore, observing a word in the right visual field goes to the left brain. This means the person could say the word out loud, as the speech and language centers are also in the left brain. They would also be able to move their right hand if, for instance, they were asked to draw the word presented to them. So far, pretty normal. Now, let us walk down the path of presenting a word to the left visual field. The visual input is sent to the right hemisphere of the brain. When asked what word was shown, the patient says nothing. The visual input, stored in the right brain, has no pathway to the speech and language center in the left brain. The patient cannot represent the information in words or speech, as these two pieces of informations are located in opposite hemispheres, unable to communicate. However, when asked to close his eyes and draw with his left hand, the patient is able draw a picture of the word. I recognize this probably sounds very confusing. Watch the video below for a visual explanation.

Split brain behavioral experiments

So with this basic physiologic understanding, let’s jump to the fun part, its implications for consciousness. For this discussion it may be helpful to invoke a particular definition of consciousness. In the words of philosopher Thomas Nagel, “an organism has conscious mental states if and only if there is something that it is like to be that organism—something it is like for the organism.” This assertion is made in his paper “What Is It Like to Be a Bat?” For example, as soon as we say, “if I could perceive via echolocation, I would understand how a bat negotiates its surroundings,” we assign some level, or type, of consciousness to the bat. It has consciousness because there is something that it is like to be the bat. This definition of consciousness is a decent starting place. While it does not violate any of my intuitions, or directly contradict my developing notion of consciousness, it does not offer much insight either. The obvious thing we must extend from this definition is that consciousness is no one thing. You and I can both be conscious, as can the bat, but there are clear and obvious differences between these incarnations of consciousness. There are levels to the game, so to speak. This goes against the materialist and rationalist tendency to discretize and demand a concrete form of things. Through this definition we are clearly allowing consciousness to take on different forms, while also retaining some element of commonality. In my own interpretation of this idea, consciousness is the awareness of what it is like to be.

Back to the split brain experiments. If we apply the above definition of consciousness to the split brain patient, we are forced to assign individual consciousness to each hemisphere of the brain. As seen in the video, when shown different words in each visual field, the cognitive processes are distinct. The left hemisphere knows the he visualized a hammer, while the right hemisphere knows he visualized a saw. Both are 100% correct, both are 100% convinced of their perceptions, and both are completely unaware of the other.

What does this do for our understanding of consciousness? For me, it shows that consciousness is differentiated from the body, while also being dependent upon it. It is detached, but receives input from the body. I visualize it as a little entity floating right above my head. It takes inputs from inside the body as well as outside, welds them into a coherent story, and then poses as the all mighty conductor of volition. It incorporates all the stimuli of the senses, the inner psychic drives and images, our history, our place in the group, our place in society, our direct environment, possible future outcomes, and possible ramifications of those outcomes. A complex data mining, data combining, and narrative building machine.

So when we split the brain, the direct bodily inputs of consciousness obviously change. It is clearly like something to be the experience of the left brain, and clearly like something completely different to be the experience of the right brain. When we split the brain, we create another instance of consciousness. We introduce another way to be, and consciousness is there for its interpretation. For it is always there, always a level removed from direct perception. Thinking about split brain as a splitting of consciousness may be a helpful visualization, but in reality we aren’t splitting consciousness, it is just there, aware of whatever inputs are available to it.

I would like to close with a bit of a thought experiment. As this post was started, where are you? That thing that is the doer, where is that located? Before I really started thinking about consciousness I would have immediately answered that question: I am in my head, of course. My thoughts have drastically changed since.

Best explorations

-Ryan; 5/16/2020

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