Twin Studies

Twin studies are studies that involve both monozygotic (identical) and dizygotic (fraternal) twins. The purpose of these studies is to measure the contribution and the effect of genetics, as opposed to environment, to a particular trait. They allow the effects of nurture which is environment and nature (heredity) to be investigated. The classical twin study relies on studying twins who are raised in the same environment like in a family and compares the similarities between identical twins who share all of their genes, with fraternal twins sharing only 50% of their genetics for a trait. By examining how often certain traits occur in identical and fraternal twins, we are able to estimate how much genes affect these traits. Researchers assume that any likeness between monozygotic twins is due to genetics. However, the modern twin studies specialize more on the pairs of identical twins who are raised apart, and therefore they do not share the same environment. An example of the modern twin studies is a psychological study called The Minnesota Study of Twins Reared Apart (MISTRA) which began in 1979, at a time when people supposed that intelligence and personalities were only influenced by the environment. The basic design of MISTRA relied on finding identical twins reared apart and seeing what traits they had in common. MISTRA had used more than 81 pairs of twins from which most of them were often separated right after infancy. For instance, genetically identical twins Jim L. and Jim S. were reared apart since infancy and were first reunited at age 39. Researchers found many interesting similarities between them like: both of them had had a dog called Toy. Each of them bit his fingernails and had headaches. Both Jims were first married to a woman called Linda and then to Betty. Each had worked at a gas station, smoked cigarettes and liked the same brand of a beer. Jim L. and Jim S. had even similar voices, gestures and mannerisms. By using twin studies we can estimate how much the particular trait is affected by genes. These studies also allow us to study the influences of genes on medical studies. Even though the twin studies might have many benefits, there are several limitations as well. The major disadvantage is that there are only a certain number of twins which means that twin studies do not represent the whole society. Therefore, the generalizability of the results may be limited. In the classical twin study, one of the main limitations is that as the twins are raised in the same environment we cannot really predict the effects of nurture on certain traits. On the other hand, a disadvantage of the modern twin studies is that the twins who were reared apart had often different personalities which must had been due to growing up in the different household then. Along with twin studies, there are many ethical issues too. In many cases, in order to conduct a psychological study, researchers decided to separate newborn twins. Sometimes, these twins weren’t even told of having a twin! So is it right to take a baby away from its parents and its twin in the name of science?

Genetics & Twins

Twin studies are studies that focus on the importance of environment and genetics as well as on the way they affect individual traits and behaviors. The classical twin study focuses on studying twins who are raised in the same environment (family). For the decades, researchers observe similarities for the particular trait between fraternal and identical twins and predict that the similarities between identical twins are due to same genes rather than environment. Modern twin studies also try to determine the effect of a person's share environment like family as well as the effect of a person's unique environment like individual events, on a trait.

Adoption studies are designed to evaluate genetic and environmental influences on phenotype.  They provide a model research where biological effects can be estimated. These studies are often very helpful in uncovering interactions between genes and environment in psychiatric and complex behavioral disorders.

MISTRA which stands for The Minnesota Study of Twins Reared Apart, is one of the most important and interesting psychological studies. This study overthrew the dogma that said intelligence and personalities were caused and mainly affected by the environment. It was designed to see how different monozygotic and dizygotic twins reared apart are. For this experiments 81 MZA and 56 DZA twin pairs were used. The twins had been separated mostly before age four. What they found was that similarities between the twins are due to genes and dissimilarities must be the result of the environment.

Stroke: An Assault on the Brain

1. Explain what happens to the brain when a stroke occurs.

The brain is damaged due to lack of blood. When the blood supply fails, nerve cells stop receiving oxygen and brain damage occurs.

2. Briefly explain the differences between the three different types of strokes.

a) Ischemic Stroke: is caused by a blood clot (thrombus) that occurs in an artery and blocks the flow of blood to a part of the brain. b) Hemorrhagic Stroke: it occurs when a blood vessel ruptures inside of the brain. c) Transient Ischemic Stroke: it's a mini stroke and it occurs when a blood clot blocks an artery for a short time.

3. Identify some of the most common risk factors - in other words, who is most likely to have a stroke?

There's two types of risk factors: controllable and uncontrollable. Controllable risk factors are high blood pressure, high cholesterol, smoking, alcohol use, diabetes and overweight. Uncontrollable risk factors are family history, age, gender, history of previous strokes.
 

4. What disabilities can result from a stroke?

Stroke may cause: problems with thinking, learning, memory, attention, paralysis (even on one side of the body), problems with understanding and speaking, emotional problems and pain.

5. What is brain plasticity and what does it mean in terms of recovering from a stroke? 

Brain plasticity is basically the ability of the brain to change, physically, functionally, chemically, throughout the life. Because of the brain plasticity, stroke patients who have lost the ability to speak or to move a limb have a chance to regain function after several weeks of convalescence (use of neuro-imaging techniques).

Sperry and Gazzaniga: The Split Brain Study

What does it mean for a person's brain to be "split"?

When a person's brain is split it means that corpus callosum which connects 2 halves of the brain is cut off.

What was the reason why this procedure was performed on patients?

When someone suffered from epilepsy (kind of a storm in the brain), doctors used to cut off corpus callosum to prevent spreading of epilepsy to the other hemisphere.

Explain one of the tests Sperry and Gazzaniga performed on these split brain patients. 

Their first patient was a soldier who had started having problems after a German soldier clocked him in the head with a rifle. After the operation Sperry and Gazzaniga ran an experiment in which this soldier was supposed to press a button whenever he saw an image. Researchers then flashed images of letters and other stimuli. For the stimuli delivered to the left hemisphere, the soldier simply pressed the button and said what he saw. It was different for the stimuli delivered to the right hemisphere. He couldn't verbally say what he saw but his left hand kept pressing the button every time an image appeared. 

What were the results of this test?

Left hemisphere is dominant for verbal processing that's why the patient's answer matched the word. The right hemisphere cannot share information with the left, so he couldn't say what he saw but he was able to draw it or press the button.

What is the reason that these results occurred?
The reason is that the brain is divided into many parts and every part of the brain has its own function. Each of the parts works independently.

What is the corpus callosum and what role does it serve in your brain?
It's a flat bundle of neural fibers that connects the left hemisphere of the brain with the right. It facilitates communication between two hemispheres.