As I was reading the text I came upon a section that I thought to be quite fascinating.
It talked about people who have a brain that functions like two different people inside
of the brain. This is of course the Split-Brain Personality. As I studied this topic in
more detail I found it to be quite broad and yet very detailed. I found that I needed a
dictionary to be able to read all of the medical journals and books that are out there,
to be able to understand what it was exactly, that I was reading. But with a little
study and research I found that this is a precise science that is still largely full of
mysteries.
The study of hemispheric asymmetry with in the cerebral cortex had long been a
fascination with the human race. The ancient Aztec cultures used to perform a type of
brain surgery on humans. This is evident from the human remains that we find with
incisions and piece's missing of the skull. Whether or not these primitive surgeries
were successful is unknown. The earliest way for man to observe the brain was by
noticing brain damage to a particular area of the brain that was damaged. Such
observations were first recorded some 5,000 years ago (Myers,1995). The most popular
case is that of Phineas Gage a railroad worker that had severe frontal lobe damage. This
happened when a rail road spike was shot through his head by a piece of dynamite.
Miraculously he lived through the experience, but with a severe change in his
personality. From this physiologists learned that personality was largely controlled
from this point namely by removing a persons inhibitions.
For the most part the brain has been a mystery that is waiting to be opened. The last
two decades have witnessed a period of research on the human cerebral functions
comparable to the great era of discovery initiated by Broca in 1861(Young, G,.
Segalowitz, S,. Corter, C,. Trehub, S,.1983). We have leaned more in the past 20 years
about the brain and it's hemispheric asymmetry than we had learned in combined previous
history.(Kosslyn, 1993). Most of this new work has been devoted to the study of cerebral
functions in adults, but recently there has been a growing interest in infants and young
children most especially among the study of hand preference. About 10 percent of the
human population in left-handed(Myers,1995). By looking at ancient writings this
right-hand preference has seemed to develop right from the start of the human race. It
also is apparent that from ultrasound devises that about 9 in 10 fetuses suck the right
hand's thumb(Myers,1995). This would lead us to believe that handedness was an inherited
trait. Their was a man by the name of George Michel, who in 1981 did a survey of new
born babies and what side of their bodies they liked to lay their heads. He found that
about two-thirds of 150 babies preferred to have their heads turned to the right while
about only one-third laid their heads to the left. In a follow up survey Michel found
that almost all of the right-sided babies were starting to reach with their right hand
and again one-third of the left sided babies were reaching with their left
hand(Myers,1995). In contrary, it is also found that handedness is one of the few genes
that are not shared by genetically identical twins. So what is it exactly that develops
handedness? Some speculate that the handedness of a person is evident in the brain and
in its specialization concerning hemispheric asymmetry. Tests reveal to us that about
ninety-five percent of right-handers process speech primarily in the left
hemisphere(Myers,1995). While the study has found that left handed people are more
likely to be a little more diverse or ambidextrous in their hemispheric asymmetry. But
as we had learned in the first chapter is this a correlation or a causation? I
personally feel that it is a correlation and not a causation. The brain is a very
flexible and delicate instrument. It has the ability to adapt and change with different
stimuli. The brain in left handed people I feel is just adapting to the use of a left
hand preference and that is why it is more likely to be ambidextrous
I would now like to talk about the asymmetry of the hemispheres. First, I will talk
about the left side of the brain and then I will talk about the right. For well over a
hundred years neuropsychologists have proposed that the left hemisphere plays a special
role in both the production and perception of language(Hellige,1993). It has often been
said that the left hemisphere is dominant for linguistic or verbal processing. This does
not mean that the right does not have linguistic or verbal skills but merely suggests
that the left is more capable and therefore more likely to process the language. This
conclusion was reached after observation of people with language disorders that occurred
after a left hemisphere was damaged. It is now a well documented fact that aphasia (the
acquired loss of language) is far more likely after left-hemisphere than after
right-hemisphere injury and that specific symptoms depends on which regions of the left
hemisphere are injured(Hellige,1993). Studies of patients with unilateral brain injury
have led to estimates that the left hemisphere is dominant for speech in approximately
ninety-five percent of right-handed adults, with the right hemisphere being dominant for
speech in the other 5 percent of right-handed adults(Hellige,1993). Such results
demonstrate that the integrity of certain areas within the left hemisphere is necessary
for the production of speech and certain other language related activities. Inside of
the left hemisphere is a spot called the Broca's area(Myers,1995). This area is named
after a French physician named Paul Broca. He reported in 1865 that damage to this area
left a person unable to form words, but were still able to sing songs and still could
comprehend speech. One would think that these two things are the same, but according to
Broca's observation this is not so. Consequently this particular area was named after
him. Latter another discovery was made by a man named Carl Wernicke. He discovered that
if damage occurred to a specific area in the left temporal lobe this left people able to
form words, but unable to make any sense of the words that they are saying(Myers,1995).
An example of this is when a patient, with this particular part of the brain damaged, was
asked to describe a pitcher of two boys stealing some cookies behind a woman's back, he
would say, "mother is away her working her work to get her better, but when she's looking
the two boys looking the other part. She's working another time"(Myers,1995) This area
was later named after this man and is now known as Wernicke's area. Although damage to
the left hemisphere is more likely to cause language disturbance than is damage to the
right hemisphere, if left brain damage occurs in childhood recovery may be dramatic and
virtually complete. The recovery in these cases is thought to be the result of rapid
assumption of language processing in the right hemisphere(Young etal.,1983) When aphasia
is associated with a stroke in adulthood, recovery is often a slow and incomplete
process. Aphasiologists question whether this form of recovery is the result of gradual
left to right switching language dominance, or rather the reorganization of the left
hemisphere. Evidence is in favor of the latter. A man by the name of Kinsbourne, who in
1971 did a study on aphasic patients and language compensations. He staged serial
unilateral intracarotid amobarbital injections on two right-handed aphasic patients. A
third patient had a left side injection only. Left-side injections did not result in
speech arrest, but arrest of all vocalization occurred with the right-side
injections(Perecman,1983). For Kinsbourne, these results indicate that in these cases
dominance for residual language had shifted to the right.
I will now talk about different aspects of the right hemisphere. The right hemisphere
has a little less organized principles and the processing elements are not as defined
but nonetheless a valuable resource which will often go untapped or underutilized by the
average person. In general, the right hemisphere controls the emotions of a
person(Perecman,83pg69). In fact there is a theory now that negative emotions are
created by the right hemisphere and the positive ones are done by the left.
Neuropsychologists have found that motion picture sequences viewed with the left visual
field are judged more negative than those viewed with the right field. Questions
concerned with negative, rather that positive, produce greater leftward eye movements.
Facial motor asymmetries are more likely to be biased to the left side for negative
expressions, such as anger, sorrow, or disgust. Where the right side is more likely to
favor the positive expressions (Perecman,1983). But in the contrary, studies have found
that damage to the right parietal region impairs the identification and production of
both positive and negative emotions, even if they are both conveyed verbally. Similar
studies have found that there is no difference in the asymmetry of facial expressions
when conveying emotions of negative or of positive nature. (Perecman,83pg70). Although
some controversy exists as to the relative contribution of each hemisphere to the
perception of emotion. The majority of experimental studies with normal subjects have
found a right hemispheric superiority for processing a diversity of emotional stimuli
including music, and facial expressions. Tonal sequences, invoking both positive and
negative moods, are rated more quickly and accurately as well as judged more emotional
when listened to on the left ear in contrast to that of the right. The left visual field
can also detect emotions of a particular face more quickly as well as more accurately
than that of the right visual field.
I, myself am more of a right brain person. The tests that we have taken in class and
all previous tests that I have taken tell me this. I think that this is why I make
decisions more based on my emotions rather than on logic. This correlates with traits of
most right-brained people. This paper has taught me a lot in the field of the brain.
Such different aspects of the brain is what make each person distinctly different and
human.
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