ease have decreased glucose metabolism in the brain
and decreased cerebral blood flow. Some persons with
schizophrenia also demonstrate decreased cerebral
blood flow. Figure 2-7 compares the images obtained
from CAT, MRI, and PET scans.
Limitations of Brain
Imaging Techniques
Although imaging techniques such as PET and SPECT
have helped bring about tremendous advances in the
study of brain diseases, they have some limitations:
- The use of radioactive substances in PET
and SPECT limits the number of times a per-
son can undergo these tests. There is the risk
that the client will have an allergic reaction
to the substances. Some clients may find
receiving intravenous doses of radioactive
material frightening or unacceptable. - Imaging equipment is expensive to purchase
and maintain, so availability can be limited.
A PET camera costs about $2.5 million; a
SPECT camera costs about $500,000. - Some persons cannot tolerate these proce-
dures because of fear or claustrophobia. - Researchers are finding that many of the
changes in disorders such as schizophrenia
are at the molecular and chemical levels
and cannot be detected with current imag-
ing techniques (Karson & Renshaw, 2000;
Malison & Innis, 2000).NEUROBIOLOGIC CAUSES
OF MENTAL ILLNESS
Genetics and Heredity
Unlike many physical illnesses that have been found
to be hereditary such as cystic fibrosis, Huntington’s
disease, and Duchenne’s muscular dystrophy, the ori-
gins of mental disorders do not seem to be that simple.
Current theories and studies indicate that several
mental disorders may be linked to a specific gene or
combination of genes but that the source is not solely
genetic; nongenetic factors also play important roles.
To date, one of the most promising discoveries is
the identification of two genetic links to Alzheimer’s
disease: chromosomes 14 and 21. Research is contin-
uing in an attempt to find genetic links to other dis-
eases such as schizophrenia and mood disorders. This
is the focus of ongoing research in the Human Genome
Project, funded by the National Institutes of Health
and the U.S. Department of Energy. This interna-
tional research project, started in 1988, is the largest
of its kind. It has identified all human DNA and con-
tinues with research to discover the human charac-
teristics and diseases each gene is related to (encod-26 Unit 1 CURRENTTHEORIES ANDPRACTICE
Figure 2-6.Example of axial (horizontal) PET scan of male patient
with Alzheimer’s disease, showing defects (arrowheads) in
metabolism in the regions of cerebral cortex of brain.