Ashley Messersmith Exam 2 Essay #1 ENGL 220
The asymmetrical cognitive abilities of the brains in human beings remain uncommitted until
about age 12 or 13 when the brain is lateralized. If the language center in the left hemisphere is
damaged when a child is eight it would be able to grow a language center in the other side of the
brain. It wouldn’t be as good, but it’d be there. If the same thing happened to a person after the
brain was lateralized, he or she would not have the versatility of being able to grow a language
center in the other side of the brain. Two genetically linked factors impact lateralization; gender
and handedness. First, females, unlike males, have some language lateralized in their right
hemispheres in addition to their left. This can work both to a female’s advantage and
disadvantage—aphasia would be a good example of this. Second, left-handers are not
necessarily contralaterally lateralized as is generally assumed. In fact, only about 15% are right
dominant, whereas, 40%+ are bilateral, and the rest are left dominant.
The first piece of evidence for lateralization patterns is aphasia which is a language disorder
resulting from damage to the brain; most likely in the left hemisphere. If a male and female both
experienced damage to the same part of the left hemisphere a female’s reaction would not be as
severe as that of the male because the female has some language lateralization in the right
hemisphere. However, if a male and female both experienced damage to the same part of the
right hemisphere, chances are that the female, unlike the male, may have a small case of
Aphasia.
The second piece of evidence for lateralization patterns is the Wada Test. The Wada Test is an
injection into the two veins at the back of the neck. An anesthetic is injected into one of the
carotid arteries, each of which is connected to a hemisphere, in order to identify which one is
connected with the language hemisphere. The language hemisphere is arrested within seconds of
the anesthetic’s injection. This test is a pre-surgery step that reveals which hemisphere should be
protected during an operation.
Electrode stimulation, a prelude to surgery, is the third piece of evidence for lateralization
patterns. Electrode stimulation provides a map of the brain. The skull cap is removed and a
cattle prod is inserted and injects electricity into the brain—measuring the electrical flow to the
brain. If it hits the speech center while the patient is speaking the patient becomes aphasic and
the surgeon can find where the speech centers are located. The patient must be conscious while
this happens. In a part where not much activity occurs, once it is touched, it hits a power surge
and starts going. Inactive centers when hit usually produce sounds, vowels, but cannot produce
anything substantial. There are no pain receptors in the brain so this is why electrode stimulation
may take place. An example of this would be from the movie Hannibal, where the Hannibal
feeds a guy his own brain but the guy remains alive.
Brain wave patterns are the fourth piece of evidence for lateralization patterns. Sensors are
placed around the head and measure electrical activity according to which hemisphere lights up.
Imagining tests, including rCBF, PET, SPECT, SQUID, and LEM, represent the fifth category of
evidence for lateralization patterns. The PET machine locates very small tumors, small injury to
bones, etc. It is sophisticated and very accurate. The rCBF measures blood flow and shows
where the language center is because the blood flow goes there. LEM reveals which hemisphere
is doing the processing. This is a less-than-accurate test that is free and can be taken by watching
which way the eyes of a suspect shift. If the eyes shift to the left when answering a question,
than according to contralateral control, the person is using the right hemisphere to answer which
hints that he is lying since the right hemisphere is responsible for controlling creativity and
imagination.
Bisected brain syndrome (split-brain), occurs when the corpus callosum that connects the
hemispheres is cut deliberately in surgery to stop epilepsy. This is not as common as it was 30
years ago because drugs are used more now. Cutting the corpus callosum keeps epilepsy from
spreading across hemispheres. Split-brain syndrome patients seem to be perfect subjects to study
in concerns of brain lateralization because neurologists can actually communicate with each
hemisphere individually. The uncontrollable hand is a common occurrence in those with
bisected brain syndrome. An example would be if the person were depressed. The right
hemisphere wants to die so the left hand (contralateral) starts to steer right, towards a cliff, but
then the left hemisphere, logic, kicks in and the right hand steers away. These two hemispheres
are not occurring simultaneously like in a normal person because the corpus callosum that
connects the two has been severed. Also, if a pear were placed in front of a split-brain patient’s
left visual field and he were asked what he saw he would say, “nothing” because communication
between his left and right hemispheres is not functioning.
Dichotic listening deals with a brain that is fully intact. According to dichotic listening tests,
REA is 2 to 1 times stronger in men than in women. When someone speaks “girl” into right ear
and “boy” into left ear, it is more likely that the person will say girl. Women may say “boy,”
however, because of the right hemisphere’s capacity for language. In women, when a word is
spoken in the left ear, she may process it faster. She cannot analyze information through the
right hemisphere, or articulate, but has an advantage because she can use her right hemisphere to
speed up the work of the left.