Split Brain Studies and the Corpus Callosum
Jay Mallonee, 2003
What is the Corpus Callosum?
The Corpus Callosum is a section of the brain which allows
the two sides of the brain to communicate and create
meaning in the world.
Imagine for a moment two people who think and behave in
very similar ways yet perceive the world a bit differently from
one another. What if they could share their thoughts, then
modify them into a single world view based on both
perceptions? This may seem weird, but your brain works this
way thanks to the corpus callosum.
Located near the center of the brain, this structure is the largest bundle of nerve fibers that connects
the left and right cerebral hemispheres, much like a bridge. Traffic flows in both directions, but instead
of vehicles traveling over the gap, it is information.
Until the early 1950s, the function of the corpus callosum had alluded scientists. No one knew what it
did, except to connect the two cerebral hemispheres. By the 1960s, scientists at least knew that nerve
fibers within the callosum connected corresponding areas in the two hemispheres but did not yet
understand the complexity involved. However, this limited knowledge was used in an attempt to help
patients who suffered from severe and constant seizures.
Normally, electrical activity in the brain flows down specific pathways. This is not so during seizures. The
electrical charges could end up anywhere in the brain and stimulate the uncoordinated muscular activity
that many people associate with a seizure. Roger Sperry was the scientist who developed a surgical
procedure to cut the corpus callosum and stop the spread of this activity from one hemisphere to the
other. This procedure was a last ditch effort to normalize the lives of seizure patients, and it was very
effective. However, there were a few unexpected results.
After surgery, some patients exhibited contrary behaviors, such as pulling their pants on with one arm
while simultaneously pulling them off with the other. Another patient began to shake his wife
aggressively with his left hand as his right hand intervened to stop the attack. These results began a
plethora of investigations which eventually lead to the understanding that each hemisphere tends to
specialize in certain activities, i.e., speech (left side) or emotional reactivity (right side).
After the patient's callosum was cut, the attack on his wife was instigated by the right hemisphere (via
his left hand) because the left hemisphere (right hand) didn't realize what was happening soon enough
to prevent it. Such a conflict ordinarily would have been resolved in the patient's brain before the
external behavior was produced.
To a greater or lesser degree, both hemispheres contribute to the initiation of a particular behavior. It is
the corpus callosum that provides the communication pathway to coordinate these activities and helps
to incorporate them into daily life. Without this brain structure, you literally have two separate
personalities in your head, each with its own agenda.
Split Brain Patients
Brain’s Processing of Information Affected by Hemispheric Transfer
Berit Brogaard D.M. Sci., Ph.D (2012)
Split-brain surgery, or corpus calloscotomy, is a drastic way of alleviating epileptic seizures, the
occurrence of sporadic electrical storms in the brain. The procedure involves severing the corpus
callosum, the main bond between the brain’s left and right hemispheres. After a split-brain surgery the
two hemispheres do not exchange information as efficiently as before. This impairment can result in
split-brain syndrome, a condition where the separation of the hemispheres affects behavior and agency.
Michael Gazzaniga and Roger W. Sperry, the first to study split brains in humans, found that several
patients who had undergone a complete calloscotomy suffered from split-brain syndrome. In patients
with split-brain syndrome the right hemisphere, which controls the left hand and foot, acts
independently of the left hemisphere and the person’s ability to make rational decisions. This can give
rise to a kind of split personality, in which the left hemisphere give orders that reflect the person’s
rational goals, whereas the right hemisphere issues conflicting demands that reveal hidden desires.
Gazzaniga and Sperry's split-brain research is now legendary. One of their child participants, Paul S, had
a fully functional language center in both hemispheres. This allowed the researchers to question each
side of the brain. When they asked the right side what their patient wanted to be when he grew up, he
replied "an automobile racer." When they posed the same question to the left, however, he responded
"a draftsman." Another patient pulled down his pants with the left hand and back up with the right in a
continuing struggle. On a different occasion, this same patient's left hand made an attempt to strike the
unsuspecting wife as the right hand grabbed the villainous limp to stop it…
Today hemisphere interaction can be studied using devices that measure the electric or magnetic fields
surrounding the skull. Unlike split-brain surgery these techniques are non-invasive. A team of
researchers from UC Santa Barbara, led by Gazzaniga, recently tested information transfer using MEG.
Language is processed in areas of the temporal lobe on the left side of the head. When you read with
your left eye, the information first ends up in the right hemisphere and must be transferred to the left
hemisphere via the corpus callosum to be processed. To test the efficiency of the hemispheric transfer
the researchers showed a randomized list of words and nonsense words to the left or right eye of a
number of research participants. They then measured how effectively the subjects would be able to
distinguish words from nonsense words. The study showed that subjects were significantly more
efficient in determining the nature of the string of letters when the information was fed directly to the
left hemisphere via the right eye. Apparently the brain has difficulties processing information that has
had to travel long distances.
The researchers didn't compare both-eye exposure to single-eye exposure. At first glance, it may seem
that it would be an advantage to get information from both eyes. However, one can also imagine that
hemispheric transfer has a hampering effect on language processing. If this is true, you might want to
wear a pirate eye patch covering your left eye when completing the verbal section of the GRE. At the
very least be careful not to shut your right eye while under time pressure.
Name:________________________________________
Block:_____________
The Split Brain
Directions: After reading the article, answer the following questions:
1. What is the Corpus Callosum? What purpose does it serve?
2. What happens if the Corpus Callosum is severed?
3. Based on the discussion we had in class, pages 41-47 in your textbook, and the information in
this article, answer the following 8-mark question:
How does the work Gazzaniga and Sperry have done support the theory of localized brain
function?
(You may need to refresh your understanding of localization of brain function by reading the
selection in the textbook.)
Answers should be at least one page in length and follow the 8-mark rubric.