Split Brain

I've been wanting to talk about this one for a while. I first read about these experiments many years ago, and they have stuck with me all this time. They are so bizarre, and yet also profoundly interesting if you care at all about figuring out what this thing we call "me" is. Let's get into it.

The Self

This is a whole topic in and of itself, but if you've followed this newsletter at all, or have interests in mindfulness or other contemplative practices, you know that this thing we call "the self" is a construct, one that is continually getting created moment by moment by the mind. In fact, one of the primary insights one can have if you have a well developed meditation practice is the recognition that there is indeed no self to find if you look for it, at least in the way we normally think of it.

Most of us have the vague sense that there is a subject, the "me", who is in the driver's seat for what we do. It's often associated with the area of the head, often behind the eyes. It does feel like there is someone looking out, pulling the strings, sort of like a crane operator in his cabin, moving levers around to generate thoughts and actions. But is there really? And if there is, is there only one of them? That may make no sense to you, but read on.

Corpus Callosum

The left and right hemispheres of the brain are connected by a bundle of nerve fibers called the corpus callosum. That's the only pathway for the two sides of the brain to share information. In the 1900s, doctors who were treating patients with severe epilepsy figured out that severing this nerve bundle in a procedure called a corpus callosotomy could have beneficial effects for those patients. Epilepsy is like an electrical storm in the brain, and when it is severe, it can rapidly move across the two hemispheres; the surgery eliminated that pathway, helping patients.

So here you have some people whose two sides of their brain can no longer communicate with each other. You probably know that the two hemispheres are responsible for different functions in humans, and the surgery led to some strange circumstances. In the 1960s, neuroscientists like Roger Sperry (who won the Nobel Prize for it in 1981) and Michael Gazzaniga studied those patients who had undergone the surgical procedure. The "split-brain" experiments challenge the common understanding of consciousness and the self. Here’s a more detailed breakdown of some of the most interesting experiments.

Split Brain Experiments

The goal of the experiments was to understand what happens when the communication between the two hemispheres is cut off. Since each hemisphere processes information from the opposite side of the body (i.e., the left hemisphere processes information from the right visual field and controls the right hand, while the right hemisphere processes information from the left visual field and controls the left hand), the researchers designed a series of clever experiments to test how the brain would handle different types of input.

1. Visual Split-Field Experiment:

This experiment involved showing images to only one hemisphere of the brain. This was done by having the patient stare at a fixed point on a screen, with images flashed either to the left visual field (processed by the right hemisphere) or the right visual field (processed by the left hemisphere).

When an image of an object (e.g., a spoon) was shown to the left visual field (right hemisphere), the patient could not verbally describe what they saw. The left hemisphere, responsible for language, had no access to the information. However, when asked to use their left hand (controlled by the right hemisphere) to pick up the object corresponding to the image from a set of items, they could correctly select the spoon, even though they couldn’t say the word "spoon."

When the image was shown to the right visual field (left hemisphere), the patient could easily name the object, since the left hemisphere was involved in both language and the right hand.

This demonstrated that the two hemispheres were working independently: the right hemisphere could “see” and understand the object, but it couldn’t use language, while the left hemisphere could use language but had no access to the information processed by the right hemisphere.

2. Dual Hand Tasks:

In another set of experiments, the researchers gave different tasks to each hand. For example, they would place a familiar object (like a key) in the patient’s left hand, and the patient could recognize and use it correctly with that hand. However, if asked what they were holding, the patient could not name it, since the right hemisphere lacks language capability.

Here's where it gets even weirder. Some of these patients reported that their hands would even act independently or in opposition to each other. For example, when getting dressed, one hand would button a shirt while the other hand, controlled by the opposite hemisphere, would begin unbuttoning it. In one case, a patient reported reaching for an object with one hand, only for the other hand to slap it away, as if the two hemispheres were in conflict. Wow.

3. Confabulation:

That's a nice word for "making stuff up".

Because the left hemisphere is the one responsible for producing speech and interpreting experiences, when it doesn’t have access to the information from the right hemisphere, it often makes up a story to explain the behavior. This is known as confabulation.

For example, in one experiment a patient was shown different images in each visual field. One half of the brain (right hemisphere) was shown a snowy scene, and the other half (left hemisphere) was shown a chicken foot. The patient was then asked to point to related images. With the left hand, the patient pointed to a snow shovel, and with the right hand, they pointed to a chicken.

When asked why they chose the objects, the left hemisphere, which controls speech, didn’t know about the snowy scene (only the right hemisphere saw it). So the patient explained their choice by saying, "The chicken foot goes with the chicken, and you need a shovel to clean out the chicken coop." The left hemisphere invented a coherent story to explain the behavior of the right hemisphere.

5. The Right Hemisphere Can Understand but Not Speak:

Another fascinating discovery was that the right hemisphere could understand language but not produce it. In some experiments, when commands were given to the left ear (which connects to the right hemisphere), patients could carry out the tasks (such as touching their nose), even though they couldn’t verbally respond or explain why they were doing so.

“Each hemisphere of a split brain can be shown to have a mind of its own, with each of the separated halves having its own private sensations, perceptions, impulses, will, and memories, all of which are inaccessible to the other half.” - Roger Sperry

So What is the Self?

I think we can agree these experiments and results are just weird, but let's go back to where we started. If you think there is a "self" associated with consciousness, e.g. a thinker of thoughts, a doer of actions, what are we to make of the split brain results? It would seem that these patients have two separate selves, one per hemisphere. They behave very differently, since they have different attributes, but they both seem to have points of view. So are there two selves? At the very least, consciousness isn't centered in one area of the brain, and there may be many processes involved. If it were possible to further separate functions of the brain, would there be more "selves" revealed?

What I find a little disturbing is that there is an illusion of unity that is formed because we place such value on verbal communication. It's the left hemisphere that controls language, and in a normal person this process integrates information from both hemispheres, creating what seems like a coherent narrative. But is it? We saw that the left hemisphere just makes up stuff when it lacks information. If the right hemisphere, which lacks language, has a point of view, is it just ignored or drowned out by the tyranny of the left hemisphere?

Conclusion

The more you learn about the world, and about yourself, the more things seem like processes rather than any fixed state. Stability is an illusion, and one that our brains are working overtime to make seem real. Inside the brain it appears the same thing is going on. Even the most basic facts about our lives, or our consciousness, are processes that are much more fluid and spread out than we might expect. We don't understand a lot of what goes on in the brain, but the fact that even a subject, a notion of self, isn't well defined is fascinating. I take that as a positive - if there is not even a fixed self, whatever stories you are telling yourself about your life and what you are doing are subject to change if you want to. If nothing is really fixed, the sky's the limit for what you might do with your life. So enjoy it!

-Scott