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Right vs Left

jrieders's picture

Up until the early 1960’s the left brain was thought to be superior to the right brain. It apparently held the sole capacity for language, higher volitional movement, and arithmetic reasoning. It was thought that the right brain lacked consciousness, and was even termed “retarded” relative to its counterpart. These conclusions were largely based on studies of patients with left hemisphere damage. At this time observations of commissurotomy or “split brain” patients, were made by Roger Sperry, Joseph Bogen, and Phillip Vogel, that shed new light on the independent functions of the right and left cerebral hemispheres, their capability to interact, and the brain’s ability to compensate for damage. A commissurotomy is the surgical severance of the corpus callosum and other nervous tissues that connect the left and right hemisphere of the brain, which is given to patients with severe epilepsy as a last resort to prevent debilitating brain damage. After a recovery period, it is extremely difficult to tell that someone has undergone such a surgery, and the left and right brain continue to interact through lower regions of the brain and something like guesswork. These patients provide unique insight because stimulus can be isolated to either the right or left side by stimulating only the left or right side of the body. This allowed researches to make clearer observations on the functions of the right and left hemispheres.
By isolating stimulus to the left eye scientists were able to determine that the right brain could read relatively simple words, understand complicated spoken language, and match images to words. Some patients were even able to spell out short words when given letters. Aside from these simple tasks, the right brain was found to excel when given spatial, imaginative, or descriptive tasks such as map making or distinguishing musical chords. It was found that the reverse was true of the left brain, that it could only accomplish simple spatial and descriptive tasks, but excelled in complex verbal and mathematical tasks. This polarity, also seen in animal studies, supported the presumption that the right brain was indeed singly accomplishing its task, but additional information provided by human studies further supports this presumption. When the patients were given follow up verbal (i.e. left brain) questions about information that was successfully processed by the right brain, they were completely unable to provide answers and could not recall the cognitive events surrounding the information and tasks. In other words, it seems very much that the right and left hemispheres are two separate entities working together only by physical connection or mutual sensory reception.
The issue then was what to think of the old left brain lesion data, which showed that people suffering from left hemisphere damage were not able to complete any of the simple linguistic tasks that split brain patients could. Did epilepsy somehow affect the typical left sided distribution of language? Sperry observed that when the right and left brain were connected, if there was damage to the left brain, linguistic ability in either the left or right brain was destroyed. However, if the hemispheres were separated, both sides exhibited linguistic ability. He hypothesized that as long as the two sides of the brain are connected, they will continue to act as one entity and carry out their respective responsibilities. But if they are separated the influence of the opposite hemisphere is disrupted, and latent ability can be tapped. This latent ability does not necessarily come without a price, in one example a student born without a corpus callosum tested above average in verbal ability and his speech ability was found in both hemispheres of the brain. Yet he tested well below average in spatial and non-verbal tasks, suggesting that speech ability in the right brain took the place of some of his spatial perception ability. This of course is only one example, and perhaps this student was simply bad at geometry!
Another interesting observation of left-right hemisphere interaction came from tasks that involved emotions. While tasks involving concrete cognitive function could be relegated and confined to each hemisphere, tasks designed to test self/social awareness could not be pinpointed to a specific region. Moreover, the information processed and the generated outputs seemed to bleed from one side to the other. For example, if a picture of a family member was shown to the left visual field (i.e. the right brain), the left side of the brain was later able to guess what the stimulus was. This leakage was associated with the lower brainstem, which raises new questions about the nature of emotions and consciousness as the lower brainstem is associated with the most basic functions necessary for survival.
While this research debunked the old theory of left brain superiority, showing that the left and right brain both have compatible and essential responsibilities and capabilities, it brings up many new questions. Further research on children who have undergone commissurotomy, as well as research on individuals born without the corpus callosum, would help to uncover the mechanisms and adaptive nature of the brain. Furthermore, these new conclusions allow for us to consider the way we observe the brain. As Sperry suggests, in the future we will not simply consider right versus left, but rather up versus down, front versus back, and the world of difference in between.

Work Cited
Sperry, Roger. Some Effects of Disconnecting the Cerebral Hemispheres. Science VOL. 12, September 24th, 1982:1223
(the same article, which was his Nobel Lecture, can be found at
Senders, Garman, Anderson, Johnson. Split Brain Consciousness. (2/25/08)
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Paul Grobstein's picture

left/right, up/down

I wonder how much of the current left/right story actually is an up/down story, ie one that has to do mostly with a I-function/rest of nervous system distinction? That would be worth exploring further.