Introduction Split Brain

This title might already sound quite bizarre to you. Isn’t it just so, that we have one brain inside our heads and that’s it? How would it be possible on earth to be walking around with two brains instead? Perhaps you are thinking about some weird science-fiction scenario where a macabre scientist glues another brain to a human head. I assure you, even though this phenomenon doesn’t occur very frequently, it does arise under fairly regular circumstances. Let’s find out how a split brain is possible.


Brain Anatomy

Let’s start out with a bit of brain anatomy. As you might already know the brain is divided into two parts called the hemispheres.

Now, the right hemisphere doesn’t have linguistic capabilities. It is in essence without language. The left hemisphere on the other hand does have language. It controls functions like vocabulary, grammar and meaning (this is the case in right-handed people, otherwise it is the other way around). Also worth noting is that the right hemisphere controls the left side of your body, from your left foot, to your left hand, all the way up to your left eye. Similarly, the left hemisphere of your brain controls your right side.

Now there is also this thing in between the hemispheres that is called the corpus callosum, which connects the two parts. It is a commissure, which means that it is a band of nerve fibers connecting the two sides of the brain. The corpus callosum contains around 300 million nerve fibers, which allows communication between both hemispheres.

Split Brain: Corpus Callosotomy

Now, you might have already started to suspect where I am going with this. What if we removed the corpus callosum? Then the left and right hemispheres are not able to communicate any longer. Could they then start to function as separate entities?

You might also start to become a bit worried. Why would Nico want to do something so diabolical, just take a brain and remove such an important component. Well, this is actually a medical procedure that is done to help people who suffer from refractory epilepsy. This is a very nasty type of epilepsy which brings forward uncontrollable seizures, that cannot be mitigated by taking medicine. The surgical procedure to resolve this is called a corpus callosotomy, and usually this is done only partially, but in extreme cases the entire thing has to be cut.

Findings of Split Brain

So what have we found? It is indeed the case that if the hemispheres are split up, that they start to function as an individual brain themselves. So these people are basically walking around with two brains inside their head. After some time, one side of their brains becomes dominant and sorta takes over. So then, it is usually not noticeable at all any more. But in the beginning, the two sides are more in competition, and this can lead to very fascinating situations. For example, a patient has once reported that when he was dressing himself, one hand was pulling his pants up, but the other hand was pulling his pants down. So the left hemisphere wanted to get dressed, but the other one wanted to stay undressed.

There are also experiments that rigorously show that it is possible to communicate something to one side of the brain, with the other part completely missing it. I give a detailed example of one of this experiments in the video, starting at around 4:00. This is a bit easier to explain with motion pictures, so I won’t bore you with the text here. But these examples clearly shows how messy the brain is, and that it can be the source of many bizarre events. We don’t know everything about the brain yet, in fact there is still a ton of stuff that we don’t know. But we are getting closer every day.

Further Reading

Another post about bizarre brain activities: brain waves.


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