Sperry's Split-Brain Research

NeuraFind’s second pick is one that demonstrates the functioning methods ,mechanisms of the brain and the role of the corpus callosum.

Before we dig into this experiment, there are a few things that we need to know.

Pre-Knowledge

Firstly, the brain is divided into two hemispheres, the left and the right. Counter-intuitively, both hemispheres do not have the same functions. This concept is called brain laterization – this is the idea that different hemispheres of the brain have separate functions.

Left Hemisphere

 The left hemisphere is the logical, analytic, and linear kind. It allows up to think in words, understanding sequencing, it is mathematical and logical.

Some of the functions linked to the left hemisphere include, reading, writing, and calculating. It performs one of the most important functions for a human, which is speech.

The thought process style for this brain is verbal and sequential. It is more reality oriented.

Right Hemisphere

This is the exact opposite of the left hemisphere. It is responsible for abstract and holistic thinking, artistic, intuitive and focuses on verbal cues. It also helps visualising concepts and things and most importantly spatial reasoning.

This helps problem-solving, reasoning, memory, and attention.

Another important thing to know is that the Left hemisphere controls the muscle on the right side of the body and the right hemisphere controls the left side of the body. This also means that data from the left eye is processed in the right hemisphere of the brain and the data from the right eye is processed in the left hemisphere. This will be important to understand the split-brain study.

Even though the two hemispheres have such contrasting roles, they do not work independently. They are connected by nerve fibres that helps transfer data between the two, so they can communicate with each other. This nerve fibre is called the corpus callosum.

Corpus Callosum

This is a large bundle of about 200 million myelinated (covered in the myelin sheath, an insulating layer that covers the nerves in the brain and the spinal cord) nerve fibres. This is what permits communication between the two hemispheres. This is mostly made of white matter. As mentioned in my earlier newsletter.

White matter is where all the communication/signal transferring happens in the brain. This is where most of the axons (the long stem part of a neuron).

Most white matter is found in the deeper tissue of the brain (the subcortical region). Gray matter on the other hand is where all the processing of information occurs. In a way, the white matter can be analogous to blood/nerves in the body – something that helps transfer information to the different organs. Gray matter on the other hand can be analogous to the organs in the brain.

Corpus callosum is the largest white matter structure in the brain with 200-300 million axonal projections.

Split-Brain Experiment

In 1950s and 1960s, Roger Sperry performed an experiment investigating the function of the corpus callosum in the brain and demonstrated brain lateralization.

He tested the effect of a damaged or absence of the corpus callosum in humans. He gathered a group of people that were either born without a corpus callosum or had the in removed due to certain circumstances. He found out that the two hemispheres functioned independently. The subjects were able to perform most functions as normal but did have some impairments.

Experimental Design

Firstly, remember the following points:

·       The right brain controls the left side of the body, and the left brain controls the right

·       The left brain is responsible for speech, but the right brain isn’t. The right brain cannot express anything via speech

·       In terms of visual field, the left brain can view everything on the right side of the visual field while the right brain is able to view the left side of a visual field.

Sperry setup a computer with images of random objects flashing on two different sides of the screen as following. In the diagram below, instead of images of objects, X and O are being used representatively.

Variation 1 – Image on only One side of the screen

In the first variation, Sperry would flash an image only on one side of the screen and ask the subject what object they saw as well as draw what they saw.

All of this was setup as following.

Variation 2 – Images flashed on both sides of the screen

In this variation, an image was flashed on both sides of the screen. Once flashed, the subject was asked to say which object they saw out loud as well as draw the object they saw.

This was setup as following.

Results

Variation 1

Let’s say that the image X was shown on the left side of the visual field.

When asked the subject what object they saw, they claimed they did not see anything.

However, when asked user to draw the object, they were able to do this correctly.

Let’s say that the image X was shown on the right side of the visual field this time.

The subject correctly said the name of the object out loud

However, when they were asked to draw this, they were unable to claiming they are unsure why they cannot draw the object.

Variation 2

After flashing both images at the same time (let’s say X was flashed on the right side and 0 was flashed on the left side).

When the subject was asked what object they say, the subject would respond that they saw X.

However, when asked to draw the object they saw, they would draw object 0.

Neuroscientific Explanation

Firstly, the experiment was based on the idea that the left brain will process the image flashed on the right side of the screen, while the right brain will process the image on the right side as shown in the diagram below.

 Its also worth noting that the right brain is not capable of controlling speech. However, both sides of the brain can control the muscles on the opposite sides of the body.

Now, in the first variation, the subject was not able to say the name of the object when the image was flashed on the left side of the visual field (left side of the screen). This is because, this information was processed in the right hemisphere and as we know, the right brain cannot control speech hence cannot output the information verbally. On the other hand, the subject can draw the with their left hand but not their right, because the right hemisphere (that processed the information) can control the right side of the muscles.

In the second variation, the same principle is used, the subject was able to draw the object with their left hand they saw on the left side of the visual field but not say it out loud. This is because, this information was processed in the right hemisphere and as we know, the right brain cannot control speech but can control the muscles on the left side of the body hence can draw it using the left hand.

Due to the absence of the corpus callosum, the two hemispheres are unable to communicate, which makes it hard to perform activities that involve a corporative effort from both hemispheres like this experiment.

Conclusion

This experiment was able to demonstrate to us how the brain works. It shows the concept of brain lateralization and the role of the corpus callosum in this process.