Question

1. Describe a visual field experiment involving a patient who has undergone the split-brain procedure. Answer should include at least one example of a question this person would not be able to answer under these conditions.
2. what role does an isotope plays in Positron Emission Tomography (PET)? Can you include an example for better clarification.

Answer 1

Split-brain surgery, also known as corpus calloscotomy, is a drastic way of alleviating epileptic seizures, the occurrence of sporadic electrical storms in the brain. The procedure involves severing the corpus callosum, the main bond between the brain’s left and right hemispheres. After a split-brain surgery the two hemispheres do not exchange information as efficiently as before. This impairment can result in split-brain syndrome, a condition where the separation of the hemispheres affects behavior and agency.

Michael Gazzaniga and Roger W. Sperry are the first to study split brains in humans.They found that several patients who had undergone a complete calloscotomy suffered from split-brain syndrome. In patients with split-brain syndrome the right hemisphere, which controls the left hand and foot, acts independently of the left hemisphere and the person’s ability to make rational decisions. This can give rise to a kind of split personality, in which the left hemisphere give orders that reflect the person’s rational goals, whereas the right hemisphere issues conflicting demands that reveal hidden desires.

Case Study

Gazzaniga and Sperry's reaearch on split-brain is being considered as one of the successful reaserch. One of their child participants, Paul S, had a fully functional language center in both hemispheres. This allowed the researchers to question each side of the brain. When they asked the right side what their patient wanted to be when he grew up, he replied "an automobile racer." When they posed the same question to the left, however, he responded "a draftsman." Another patient pulled down his pants with the left hand and back up with the right in a continuing struggle. On a different occasion, this same patient's left hand made an attempt to strike the unsuspecting wife as the right hand grabbed the villainous limp to stop it. Split personality is a rare consequence of a split brain. In some cases, impaired inter hemispheric communication leaves personality intact but still allows people to use the two hemispheres to complete independent intellectual tasks.

The hemisphere interaction can be studied using devices that measure the electric or magnetic fields surrounding the skull. Unlike split-brain surgery these techniques are non-invasive. A team of researchers from UC Santa Barbara, led by Gazzaniga, recently tested information transfer using MEG. Language is processed in areas of the temporal lobe on the left side of the head. When you read with your left eye, the information first ends up in the right hemisphere and must be transferred to the left hemisphere via the corpus callosum to be processed. To test the efficiency of the hemispheric transfer the researchers showed a randomized list of words and nonsense words to the left or right eye of a number of research participants. They then measured how effectively the subjects would be able to distinguish words from nonsense words. The study showed that subjects were significantly more efficient in determining the nature of the string of letters when the information was fed directly to the left hemisphere via the right eye. Apparently the brain has difficulties processing information that has had to travel long distances. The researchers didn't compare both-eye exposure to single-eye exposure. At first glance, it may seem that it would be an advantage to get information from both eyes. However, one can also imagine that hemispheric transfer has a hampering effect on language processing.

POSITRON EMISSION TOMOGRAPHY

A POSITRON EMISSION TOMOGRAPHY (PET) scan is a type of nuclear imaging test that shows the metabolic activities of your brain. In other words , we can say PET shows energy Usage of the Brain.While X-ray, CT, and MRI scans look at the anatomy of your brain,It gives your information regarding working of brain .It integrates two technologies to view your body: computed tomography (CT) and a radioactive material called a tracer. The tracer is what allows doctors to see how your body tissues absorb and use different chemicals in real time.

Before the PET scan, a tracer is injected into your bloodstream (similar to a contrast agent in CT or MRI scans). Once the tracer is absorbed in your body, a ring-shaped scanner is positioned over the body area. The tracer is radiolabeled, meaning it emits gamma rays that can be detected by the PET scanner. The computer collects the information emitted by the tracer and translates it into two-dimensional cross-sections. The radioisotopes used in PET to label tracers are 11C, 13N, 150, and 18F (carbon, nitrogen, oxygen and 18F used as a substitute for hydrogen). These radioactive forms of natural elements will pass safely through your body and be detected by the scanner. Various drugs and other chemicals can be labeled with these isotopes. The type of tracer used depends on what your doctor wants to measure. For example, if your doctor is looking at a tumor, he or she might use radio labeled glucose (FDG) and watch how it is metabolized by the tumor.

PET scanning allows doctors to measure a range of activity including blood flow, blood volume, oxygen usage, tissue pH (acidity), glucose (sugar) metabolism, and drug activity. PET is very useful in watching the activity of cancerous tumors. Because malignant cells grow at such a fast rate, they metabolize more sugar than normal cells and can give your doctor a glimpse into how aggressive a tumor is or how its growth is slowed by treatment therapies.

Another common use for PET is for pre surgical evaluation of medically uncontrolled seizures. By detecting metabolic changes in the brain, the surgeon can pinpoint the non functioning area of the brain causing seizures.

HOW IT WORKS

First, you will receive an injection of a small amount of radioactive tracer. You'll be asked to rest for about 30-45 minutes until the tracer reaches your brain (2 hours to be absorbed by bone). Next you'll lie comfortably on a table that moves slowly through the PET scanner. Be sure to remain as still as possible so that the machine can take accurate pictures. Depending on the information your doctor needs, you may be asked to perform certain tasks like read or speak to activate specific areas of your brain.

Once the scan is complete, you can leave. Be sure to drink plenty of fluids to flush out any tracer left in your body.