Essay/Term paper: Hemispheres of the brain

Essay, term paper, research paper:  Biology

Hemispheres of the Brain


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.