Schizophrenia

Schizophrenia researchers have two major theories about the way that genes play a role in causing schizophrenia. Both theories assume that inherited genes cause the brain of a person with schizophrenia to develop in an abnormal way. According to one theory, the person develops an abnormal brain structure, meaning that the shape and size of certain parts of the brain may be different from those in a normal brain.

The other theory suggests that the activity of certain chemicals in the brain, called neurotransmitters, may be abnormal. Neurotransmitters carry messages to different parts of the body They play an important role in emotions, movement, learning, and memory.

Brain Structure and Activity

Scientists have developed several techniques for taking pictures of the brain. One of these techniques, called MRI (magnetic resonance imaging), uses magnetic fields and radio waves to produce pictures of the brain. Another technique is called PET (positron emission tomography). This technique uses radiation to measure how much activity is occurring in certain parts of the brain.

Studies using MRI and PET have found differences between the brains of people who have schizophrenia and people who do not. Researchers have reported that certain structures in the brain may be smaller in schizophrenia sufferers and that the spaces between structures (called ventricles) may be larger. Also, studies using PET have found that certain parts of the brain are less active in people with schizophrenia than in healthy people.

The story is not so simple, however. Brain structure abnormalities have not been found in all individuals with schizophrenia (that is, there are people with schizophrenia whose brains appear to have the same structure as that of a healthy person). In addition, some similar brain abnormalities have been found in patients who are not suffering from schizophrenia but have other disorders, such as bipolar disorder and Alzheimer's disease.

Some studies suggest that certain differences in brain structure and activity might be linked with specific schizophrenia symptoms. For example, people who have disorganized speech are likely to have abnormalities in one area of the brain, and people who have mostly negative symptoms are likely to have abnormalities in another.

This type of research is still relatively new. As technology improves and machines that produce clearer pictures of the brain and its functioning are developed, it is likely that the role of brain abnormalities in schizophrenia will become clearer.

Neurotransmitters

Schizophrenia researchers believe that at least some of the symptoms of schizophrenia may be caused by having too much of a neurotransmitter called dopamine in the brain. Several observations led to this theory. First, drugs called amphetamines, which cause a rise in dopamine levels in the brain, can cause a person to have symptoms that look like those of schizophrenia. Second, if a person who suffers from schizophrenia takes a drug that increases dopamine levels in the brain, his or her symptoms often become worse. Third, it is now known that drugs that are helpful in reducing schizophrenia symptoms block dopamine action. See chapter five for more information about drug treatments for schizophrenia and how they work.