The independent functioning of the left and right hemisphere when no longer connected by the corpus callosum. The human brain is a dynamic and elastic processing unit that manages the great extent of human life. This entails both conscious and unconscious functioning of each human system. For example, the brain controls emotions through behaviors, physiological responses (both autonomic and hormonal), and feelings in response to stimuli from the environment (Carlson, 2011). The human brain is constructed of two major hemispheres, each linked to functional processing of opposite sides of the body.
The two hemispheres are linked by a dense bundle of nerves referred to as the corpus callosum, or “hard-skinned body. ” Though, the human brain should not be thought of as two dependent hemispheres connected by a bridge of dense neuronal fibers because even when the bridge is cut each hemisphere is able to perform independent of the other. Each hemisphere has its own distinct characteristics and specialized abilities, as demonstrated by split-brain patients who have had their corpus callosum severed, in most cases to alleviate extreme epilepsy (Bainbridge, 2008).
Split-brain patients show surprising responses to experiments designed to isolate each hemisphere to process information on its own; such experiments have uncovered that while the human brain has specialized interworking parts, the left hemisphere is the literal, talkative side while the right hemisphere interprets information in a more relational manner and is unable to verbalize. Maurice Ravel, a famous composer, suffered a stroke in 1933. As a result of his stroke, Ravel found himself unable to compose music.
Worse, Ravel’s ability to enjoy music was in no way compensated and he could still dream up his music ideas, but was unable to transfer any idea from thought to paper. Ravel could no longer write or perform his musical genius. Neurologists believe Ravel’s stroke disabled the left hemisphere of his brain where musical sound is translated and broken down into symbolic parts. The right hemisphere is utilized to enjoy music, but the left is needed to work out notes and instrumental movements.
Maurice Ravel was also severely handicapped in his ability to manipulate written language, taking a recorded eight days to write a fifty word letter (Johnson 158-9). The right and left hemispheres play different roles in processing information; when separated the two halves can work separately to make whole understandings of processed stimuli, but if damaged a specialized unit of the brain cannot be easily replaced. Patients who undergo split-brain surgery do not have any noticeable ill effects: personality, memory, or ability to live daily life does not change.
Split-brain patients were tested by Gazzaniga and Smylie for facial recognition by asking patients to identify a face on a board of 10 photos after an image had been flashed to either the left or right visual field for 120msec; the research indicated only that the left hemisphere has slight advantage over the right in remembering faces in this way (Bruyer, 1986). R. Sperry conducted research on cats with split brain and found that there is no difference in the ability for the cat to learn with either hemisphere.
In R. Sperry’s experiments the brains of cats were surgically manipulated so the connection between hemispheres and the optic nerves were severed so only one hemisphere received data from one eye. The cats were blindfolded on one eye and taught to run a maze to find food. When the blindfold was reversed so the cat could only see out of the opposite eye, the cat was unable to identify its path to food and had to relearn the entire maze (Gazzaniga 1967). In an experiment conducted on split brain patients by D.
Zaidel, pictures of faces were distorted by moving facial structures such as the nose or mouth to places were they did not belong. For example, the mouth would be moved to the position where the nose should be. The pictures were shown to split brain patients with a specialized lens that only allowed a single hemisphere to interpret the information. When patients were shown images through the left hemisphere view and asked to point to a structure on the face, such as the nose, the patient was able to correctly identify the nose on the distorted image.
When viewing the image through the right hemisphere view and asked to point to a structure on the face the patients responded by pointing to the position where the nose, or other structure, should be on the face instead of where the structure had been moved to in the distorted image. This study represents that the left hemisphere processes information in a literal manner while the right hemisphere processes in a more relational manner (Zaidel, 1994).
Experiments done at the Split Brain Institute conducted on a split brain patient has concluded that the left hemisphere of the brain controls the conscious aspect of human behavior while the right hemisphere is capable of interpreting stimuli but not able to make its analyses known either verbally or consciously. The method of the experiment entailed the patient look at a fixed point on a screen as images were flashed either on the left or right side of the visual field.
The images were shown only long enough to be perceived by the eye closest to that visual field and the images were spaced in such a way that no overlap could occur in peripheral perception by the opposite eye. This experimental method ensures that stimuli are received by only a single hemisphere of the brain. The results of this experiment are illustrated in Table 1. In manipulation one the patient is flashed the image on the left or right visual field and then asked what he saw. In manipulation two the patient is flashed the image, asked what he saw, and then asked to retrieve an object from behind a screen where the patient cannot see.
Table 1. Manipulation 1| Visual Field| Hemisphere| Understanding| Verbalize| Item Retrieved| The word “sophisticated”| Left| Right| No| No| N/A| | Right| Left| Yes| Yes| N/A| The math problem 40/10| Left| Right| No| No| N/A| | Right| Left| Yes| Yes| N/A| An image of a heart| Right| Left| Yes| Yes| N/A| Manipulation 2| Visual Field| Hemisphere| Understanding| Verbalize| Item Retrieved| The phrase “a dangerous anaconda”| Left| Right| Yes| No| A toy snake| | Right| Left| Yes| Yes| A toy snake| The math problem 1+2| Left| Right| yes| No| Three sausages| | Right| Left| Yes| Yes| The number 3|
An image of an ice cream cone| Left| Right| Yes| No| An Ice Cream cone| The data suggests that the right hemisphere is able to understand visual cues, but is not able to manipulate verbal language. The left hemisphere is able to use verbal language to bring visual cues into the conscious of a patient with split-brain. The right hemisphere may not be able to verbalize, but it is able to read. The fact that the right hemisphere is not illiterate suggests that it is not completely oblivious to language.
A hypothesis to the reason for this is that the right hemisphere may not be able to produce speech. Further investigation could be done to the origin of the brain region that controls the vocal chords. Also, MRI scans could be used to monitor the active regions of split-brain patients while talking. To further the understanding of split-brain processing two experiments could be carried out to test the comprehensive language skills of the right and left hemisphere. The patient would be blindfolded so only one eye and, hence, one hemisphere is allowed process the information.
First, the patient is shown an image and verbally asked a question pertaining to the image and asked to circle the answer written on a provided piece of paper. Second, the patient is shown a different image and asked to read and answer a simple multiple choice question pertaining to the image. The patient would be asked to do this with the hand corresponding to the processing hemisphere. An example would be to show a split-brain patient with one eye blindfolded a picture of a pig and ask “what is shown? the answer would be to circle “pig. ” The results should demonstrate that both hemispheres are able to read and comprehend written information. This hypothesis is stemmed from the research by the Split Brain Institute that both hemispheres can comprehend written stimuli. The human brain has evolved as two separate functional units; each with its own specialized curriculum. A dense bundle of neurons, the corpus callosum, has also evolved to bridge the gap between the right and left hemisphere.
A human is perfectly capable of living a fully functional life without the connecting bridge; which begs the question of why the connection even formed. The answer has been shown through research on split-brain patients that demonstrate that while the hemispheres can function independent of one another the distinct tasks performed by each is performed with better success when coupled together. References Bainbridge, David. Beyond the Zonules of Zinn: a Fantastic Journey through Your Brain. Cambridge, MA: Harvard UP, 2008. 67-72. Print. Bruyer, Raymond. The Neuropsychology of Face Perception and Facial Expression. Hillsdale, NJ: L. Erlbaum Associates, 1986. Print. Carlson, Neil R. , and Neil R. Carlson. Foundations of Behavioral Neuroscience. 8th ed. Boston: Allyn & Bacon, 2011. 287. Print. Gazzaniga, M. (1967). The spilt brain in man. Scientific American, 217(2), 24-29. Retrieved from PsycINFO database. Johnson, Steven. Mind Wide Open. New York: Scribner, 2004. Zaidel, Dahlia W. Neuropsychology. 2nd ed. San Diego: Academic, 1994. 1-5. Print.
