Split-Brain Patients and The Effects of a Severed Corpus Callosum

Severed

Corpus Callosum

• The Corpus Callosum is a large band of neural fibers which connects the left & right hemispheres of the cerebrum
• It is essential for communication between the two hemispheres
• When the CC is severed, patients experience several serious long-term effects

(usually severed as a treatment for epilepsy)

Michael Gazzaniga and Roger Sperry are considered to be the most influential figures in split-brain research. They started studying in the 1950's, focusing on each of the hemisphere's respective abilities. The results showed a pattern that severing the entire corpus callosum blocks the interhemispheric communication of perceptual, sensory, motor, and other forms of information in a dramatic way. This allowed Gazzaniga and Sperry to gain insights into hemispheric differences, as well as the mechanisms through which the two hemispheres interact.

Memory: Memory of split-brain patients is generally lower than normal, though better than in patients with amnesia.

Control: In general, split-brain patients behave in a coordinated, purposeful and consistent manner, despite the independent, usually different and occasionally conflicting processing of the same information by two disconnected hemispheres. When two hemispheres receive competing stimuli at the same time, the response mode tends to determine which hemisphere controls behavior.

Attention: Experiments on spatial attention confirm the existence of two different attentional systems in the two hemispheres. The right hemisphere was found superior to the left hemisphere on modified versions of spatial relations tests. Mental imagery is specialized: the right hemisphere was found superior for mental rotation, the left hemisphere superior for image generation.

In a person with a 'normal' brain, information from the left visual field (you see it with your left eye) is processed in the right hemisphere, and vice versa. With a severed CC, this process is disrupted.

For a person who was asked to describe/differentiate split pictures, when his corpus callosum has been cut, he could speak or describe what he has seen in his right eye (because speech is located in the left part of the brain), but if he was asked to visually point what he was saying, he would point out what his left eye saw because his visualization is located in his right brain.

Most research in this field has been done by Michael Gazzaniga. One main example of his work is patient 'J'.

One of the experiments involving J attempted to determine each hemisphere's ability to perform simple math on its own. A math problem was presented in the center of the screen, followed by a central cross hair (splitting the screen). After looking at the problem, a number presented as the answer was shown to each hemisphere (opposite visual field) with J's vision fixated on a central cross hair. Probes (stimuli) were then presented for 150 milliseconds to either the left visual field/right hemisphere or to the right visual field/left hemisphere . The position of the probe fell outside any binocular (using two eyes) vision zone, to ensure that stimuli were perceived only by the hemisphere coordinating with the stimuli. J was instructed to press a certain key if the answer shown was the correct, and another key if the answer was incorrect. Results showed that the effects of visual field was significant, with performance of the left hemisphere being better than that of the right hemisphere. The left hemisphere correctly chose the correct answer on all four arithmetic operations approximately 90% of the time while the right hemisphere was at chance. This suggests that the left hemisphere is better at calculations, thus it being called the 'math and science' brain.

As with any other disorder, this makes people more likely to have a prejudice. Also, split-brain patients have a harder time with day-to-day life, since they often cannot identify simple obects if it was presented to the wrong visual field. Split-brain patients have to think very consciously about the most basic of functionalities.

Visual Fields

Overview

HISTORY

What is the CC?

IN OTHER WORDS....

Lexi Hoven, 4B

Patient J

Social Implications & Daily Life

WORKS CITED

Funnell, M. G. (2002). Mike or Me? Recognition in a Split-Brain Patient.. Nature Neuroscience,

Hamilton, C. R., & Vermeire, B. A. (1988). Hemispheric Specialization in Monkeys. Science,

Hock, R. R. (2009). 40 Studies That Changed Psychology. (6th ed.). Saddle River, New Jersey: Pearson/Prentice Hall.

Myers, D. G. (2004). Psychology. (7th ed.). New York: Worth.

Strauss, E. (1998). Languange of a Split-Brain. In Science.