Studying the Brain: Learn It 2—Split Brain Research and Neuroplasticity

Split Brain Research

Recall that the two hemispheres of the brain are connected by a thick band of neural fibers known as the corpus callosum, consisting of about 200 million axons. The corpus callosum allows the two hemispheres to communicate with each other and allows for information being processed on one side of the brain to be shared with the other side. 

Illustrations (a) and (b) show the corpus callosum’s location in the brain in front and side views. The corpus callosum sits in between the right and left hemisphere of the brain and slightly more towards the front of the brain than the back. Photograph (c) shows the corpus callosum in a dissected brain.
Figure 1. (a, b) The corpus callosum connects the left and right hemispheres of the brain. (c) A scientist spreads this dissected sheep brain apart to show the corpus callosum between the hemispheres. (credit c: modification of work by Aaron Bornstein)

Normally, we are not aware of the different roles that our two hemispheres play in day-to-day functions, but there are people who come to know the capabilities and functions of their two hemispheres quite well.

split brain

There are instances in which people—either because of a genetic abnormality or as the result of surgery—have had their corpus callosum severed so that the two halves of the brain cannot easily communicate with one another. For example, in some cases of severe epilepsy, doctors elect to sever the corpus callosum as a means of controlling the spread of seizures. While this is an effective treatment option, it results in individuals who have “split brains”. The rare split-brain patients offer helpful insights into how the brain works.

For instance, a split-brain patient is unable to name a picture that is shown in the patient’s left visual field because the information is only available in the largely nonverbal right hemisphere. However, they are able to recreate the picture with their left hand, which is also controlled by the right hemisphere. When the more verbal left hemisphere sees the picture that the hand drew, the patient is able to name it (assuming the left hemisphere can interpret what was drawn by the left hand).
Simple drawing showing the setup of an experiment for split brain patients. The person is looking at a screen and sees a smiley face on the left side. They person says they saw nothing, but is able to draw the smiley face with their left hand.
Figure 2. One of the most well-known split-brain findings is that the patient claims verbally not to have seen the stimulus in the left visual field, yet indicates the identity of it with their left hand. This suggests that the left hemisphere (controlling verbal output) is blind to the left visual field, while the right hemisphere (controlling the left hand) does perceive it.

Consider this striking example: a split-brain patient is seated at a table and an object such as a car key can be placed where a split-brain patient can only see it through the right visual field. Right visual field images will be processed on the left side of the brain and left visual field images will be processed on the right side of the brain. Because language is largely associated with the left side of the brain the patient who sees car key in the right visual field when asked “What do you see?” would answer, “I see a car key.” In contrast, a split-brain patient who only saw the car key in the left visual field, thus the information went to the non-language right side of the brain, might have a difficult time speaking the word “car key.” In fact, in this case, the patient is likely to respond “I didn’t see anything at all.” However, if asked to draw the item with their left hand—a process associated with the right side of the brain—the patient will be able to do so!

Though this video is old, it does a great job showing the challenges facing a split-brain patient shortly following the surgery to sever her corpus callosum and demonstrates the visual field study explained above.
You can view the transcript for “Split Brain mpeg1video” here (opens in new window).

Neuroplasticity

Bob Woodruff, a reporter for ABC, suffered a traumatic brain injury after a bomb exploded next to the vehicle he was in while covering a news story in Iraq. As a consequence of these injuries, Woodruff experienced many cognitive deficits including difficulties with memory and language. However, over time and with the aid of intensive amounts of cognitive and speech therapy, Woodruff has shown an incredible recovery of function (Fernandez, 2008, October 16).

One of the factors that made this recovery possible was neuroplasticity.

neuroplasticity

Neuroplasticity refers to how the nervous system can change and adapt. Neuroplasticity can occur in a variety of ways including through developmental processes or in response to some sort of damage or injury that has occurred. Neuroplasticity can involve the creation of new synapses, pruning of synapses that are no longer used, changes in glial cells, and even the birth of new neurons. Because of neuroplasticity, our brains are constantly changing and adapting, and while our nervous system is most plastic when we are very young, as Woodruff’s case suggests, it is still capable of remarkable changes later in life.

Watch this video about another patient who underwent a dramatic surgery to prevent her seizures. You’ll learn more about the brain’s ability to change, adapt, and reorganize itself, also known as brain plasticity. You can also watch an updated video about Jody here.

You can view the transcript for “Brain Plasticity – the story of Jody” here (opens in new window).