SoTD 33: Split Brain

Introduction

index — Image credits: https://library.neura.edu.au/browse-library/physical-features/brain-regions/corpus-callosum/

Dr O’Connor said “Karen what are you doing? your hand is undressing you”. Until he said that, I had no idea that my left hand was opening up the buttons of my shirt. “So I started rebuttoning with the right hand and as soon as I stopped, the left hand started unbottoning them”.

Karen had suffered from epilepsy since she was 10 and at 27, had undergone a drastic procedure to reduce her seizures. The procedure known as ‘corpus callosotomy‘ involved severing the band of fibrous tissue that connected both halves of the brain. Indeed this was not an unusual procedure at the time. Most patients seemed to lead normal lives, one doctor even remarked that ‘the function of the corpus callosum seems to be to spread seizures from one side of the brain to another‘. And it did cure Karen of her epileptic seizures but it left her with a whole different problem – the split brain.

11221318195026390-thumb400 — Image credits: https://www.studyblue.com/notes/note/n/split-brain/deck/11171725

Roger W. Sperry, who had diagnosed Karen’s condition (he later tragically died from a mental ailment himself) worked with Micheal Gazzaniga and were the first people to study split brains. Their research showed that patients who had undergone a complete callosotomy suffered from a condition known as split brain syndrome. In this, the right half of the brain (referred from here as right brain) which controls the left leg and left hand acts independently of the left brain which controls the other two limbs.

The Brain has dedicated regions, but not quite

Image credits: http://prodpod.net/2017/02/19/prodpod-episode-104-myth-left-right-brain/

In pop culture, Its common to see that people are described as being ‘left brained’ and ‘right brained’. Several self help books have been published on the subject and it is said that the left half of the brain is the analytic half which controls things like mathematics, science and logical thinking while the right side is more ‘artsy’ and logical. This is most certainly not true , fMRI studies have been done and the entirety of the brain is involved to a degree in all tasks we do. Furthermore, the distinction over what is logical vs what is creative is a very fuzzy one – who can say that mathematics does not require a degree of creativity?

However, as with many other things the above myth is rooted in a kernel of truth. Quoting the Wikipedia article on Lateralization of brain function

The lateralization of brain function is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. The medial longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. Although the macrostructure of the two hemispheres appears to be almost identical, different composition of neuronal networks allows for specialized function that is different in each hemisphere.

To simplify, while it is not true that the brain has totally exclusive sections for different functions, there are neuronal sections which correspond to certain functions in humans ( For example, Broca’s and Wenicke’s areas found in the left brain correspond to speech in most normal human beings ). There are complications though, Left handed people often have the speech center on the right side of the brain. Some people even have speech centers on both halves of the brain. There are even people who function normally with very little brain tissue who seemingly lead normal lives.

FrenchBrain — French man with almost no brain tissue.

There was a famous case of a french man who barely had 10% brain tissue but had a normal life and had an IQ of 75, which is lower than the average of 100 but is not classified as mental retardation. The man reportedly lead a pretty normal life.

The key takeaway point is that brains are highly adaptable and when there are anomalies, they often make new neural connections that allow people to function normally. With that being said…..

Split brain experiments are really creepy

Most patients who undergo a callasotomy lead perfectly normal lives – this is expected as the two half of our brains receive nearly the same input anyway. We have two eyes which supply optical information, two ears and the sense of smell is governed by both halves. Not to mention the whole network of sensory neurons along our body that are responsible for the sense of touch. However, with a proper science experiment sensory inputs can be controlled and it reveals the existence of two different personalities in the same person!

Gazzaniga and Sperry’s research is now legendary. They once interviewed a young participant named Paul S who had two fully functional speech centers in his brain – which allowed them to question the left and right brain separately . When they asked the right side what the patient wanted to be when he grew up, he replied ‘an automobile racer’. When they questioned his left side he replied ‘a draftsman’.

Another patient tried to pull down his pants with his left hand while the right hand tried to pull it up, on another occasion this man tried to hit his wife with his left hand while the right hand tried to stop him.

It must be noted that split personality is a very rare trait among split brain patients. Quoting psychology today:

An MRI scan of the savant, Kim Peek, who lent inspiration to the fictional character Raymond Babbitt (played by Dustin Hoffman) in the movie Rain Man, revealed an absence of the corpus callosum, the anterior commissure and the hippocampal commissure, the three cables for information transfer between hemispheres. As a consequence of this complete split, Peek, who sadly died last year, was able to simultaneously read both pages of an open book and retain the information. He apparently had developed language areas in both hemispheres. Peek was a living encyclopedia. He spent every day with his dad in the library absorbing information. Among his most impressive feats was his ability to provide traveling directions between any two cities in the world.

The two halves of our brain can fight

Image credits: https://knowingneurons.com/2014/07/23/the-split-brain-making-two-hemispheres-whole/

As the left side of the brain has the ‘speech center’ , the right brain is mute (it cannot speak) so this leads to some very interesting consequences.

Sperry performed an experiment in humans to further study the ability of the right hemisphere to recognize words. During that experiment, Sperry asked volunteers to place their left hand into a box with different tools that they could not see. After that, the participants saw a word that described one of the objects in the box in their left field of view only. Sperry noted that most participants then picked up the needed object from the box without seeing it, but if Sperry asked them for the name of the object, they could not say it and they did not know why they were holding that object. That led Sperry to conclude that the right hemisphere had some language recognition ability, but no speech articulation, which meant that the right hemisphere could recognize or read a word, but it could not pronounce that word, so the person would not be able to say it or know what it was.

In another very striking experiment, Sperry asked a patient to solve a jigsaw puzzle which required putting pieces in a particular order after seeing an image. Sperry first asked the patient to solve the puzzle with his left hand (which is controlled by the right side of the brain) and the patient did it pretty easily. However when he asked the patient to solve the puzzle with his right hand (which is controlled by the left side of the brain) he didn’t have a clue on what to do, and when his left hand tried to help the right, but the right did not want the help so they ended up fighting like two young children.

Experiments like this led Sperry to conclude that “each hemisphere is a conscious system in its own right, perceiving, thinking, remembering, reasoning, willing, and emoting”. In 1981 Sperry received a Nobel prize for his work.

The brain is really good at making things up and this raises questions on free will

In one of the first experiments of his career, Gazzaniga interviewed a young patient named WJ. He held up a spoon to the side associated with the left brain, and asked the patient what it was . The patient replied normally : “A spoon”.

However when it was held up to the part that corresponds to his right brain, the patient couldn’t tell what it was at all- even though the patient had already seen the spoon.

In another experiment, he showed a word to a patient corresponding to the right brain while closing the eye associated with the left brain. The word said “Walk”. The patient promptly began to walk. When asked why he was walking, the patient made up an arbitrary reason: “I wanted a coke”. This was a pretty shocking result, the left brain didn’t really know what the body was doing but promptly made up an excuse to describe what the patient was doing anyway.

This lead Gazzaniga to classify the two halves.

The right, he says, “lives a literal life.” It doesn’t extrapolate, it doesn’t narrate, it doesn’t generalize. It registers in an exact, concrete fashion what’s going on around it.

The left hemisphere plays a different role. It’s our resident storyteller. “The left hemisphere was the intellectual,” Gazzaniga discovered. It is our brain’s “interpreter.”

It’s the left brain that spins a narrative out of all the disconnected bits of information swimming up into our conscious view. The funny thing, however, is that the stories the left brain produces are largely if not entirely wrong.

“The reality is, listening to people’s explanations of their actions is interesting—and in the case of politicians, entertaining—but often a waste of time,” he writes.

The reason for this is that the left brain works with whatever becomes conscious, but consciousness is the ultimate slow poke. It lags behind. It’s walking while the non-conscious brain is sprinting to the finish line, processing what’s happening around us, making a decision about how to respond, even beginning to execute that response. Our conscious awareness is the last to find out.

What we think we think may only be a product of our left brain trying to make sense of what the hell is going on.

How do people with a callasotomy lead a normal life then?

If one half of the brain controls the limbs of the other side of the body, how are patients able to walk? use their hands? Infact, outside lab settings it is often very hard if not impossible to differentiate between split brain and normal patients.

Image credits: http://www.differencebetween.net/science/difference-between-pons-and-medulla/

The reason is that the corpus callosum is not the only region that joins the two halves of the brain together. There is the cerebellum (which regulates breathing among other things) and the brain stem (the medulla). So even in a split brain person, there is always some degree of communication between both halves of the brain. And before you ask, no, it is not possible to surgically split the brain along the brain stem – the patient will die.

In conclusion, though we do not quite have two personalities, we do have two sections of the brain working in unison. They co-operate , register information and ultimately, shape the way we see our world. Research in this area has dwindled, because there are far less treatments of epilepsy by severing the corpus callosum. There are non surgical methods available. However some research still goes on to this day with the few patients of callosotomy who are still around, and the few people who are sometimes born without a corpus callsum (Kim Peek).

Thanks for reading! 🙂