Ch 11 - Jeff Standen

harmed by certain experiences.
In the case of depression, the disorder has been linked to
biological factors such as genetic inheritance and
imbalances in neurotransmitter chemicals and hormones.
Genetic inheritance
According to the biological model, the presence of certain
genes can predispose people to psychological disorders. In
other words, certain genes can make people more
vulnerable to disorders. Three types of studies - family
studies, adoption studies and twin studies - have provided
evidence to support this view.
Family studies In this type of study, the family tree of a
person with a psychological disorder is traced to see if the
disorder 'runs in the family'. Family study evidence suggests
that a person is ten times more likely to suffer from a mood
disorder such as depression if a parent or sibling (brother or
sister) has a similar disorder (Weissman, 1987). The problem
with these studies is that families tend to share home
environments and this, rather than genetic inheritance, may
cause disorders to run in the family.
Adoption studies These studies compare people who have
been adopted with their biological and adoptive parents.
Since they were raised apart from their biological relatives,
similarities with their biological relatives would indicate
genetic influences. In terms of depression, most studies
show a higher rate of depression in their biological relatives
- up to 20% of those relatives suffered from the disorder
compared with 5-10% of their adoptive relatives, which is
the rate for the general population (Harrington et al., 1993).
The problem with evidence from adoptive studies is that
unless the children have been adopted at or near birth, they
have shared part of their life with their biological families.
As a result, they may have learned abnormal behaviour
from their biological parents. Again, it is difficult to separate
genetic and environmental factors.
Twin studies These studies investigate how likely it is that
pairs of twins share the same disorder. They compare
identical (monozygotic) twins who have the same genes and
fraternal (dizygotic twins) who share around 50% of their
genes. If genes are a factor in psychological disorder, then
we would expect a higher proportion of identical twins to
share a disorder. A number of studies have confirmed this.
For example, a study based on nearly 200 pairs of twins
found that when an identical twin had depression, there was
a 46% chance that the other twin would also have the
disorder. The figure for fraternal twins was 20% (McGuffin
et al., 1996).
However, twins not only share all or many of their genes,
they also share much of their environment. Even when
raised apart, they often live in the same neighbourhood, go
to the same school, and spend time together. Again, it is
difficult to separate genetic and environmental influences. In
addition, samples of identical twins raised apart are small,
so making it difficult to draw firm conclusions.
Biochemistry
The biological model suggests that psychological disorders
may be due to an imbalance of chemicals in the nervous
system and the endocrine system. In other words, there may
be too much or too little of certain neurotransmitter
chemicals and hormones. These biochemicals affect mood
and behaviour. (See Chapter 7, pp 94-98, for a discussion of
neurotransmitters and hormones.)
Neurotransmitters One theory links depression to low levels
of the neurotransmitters serotonin and noradrenaline.
However, the relationship between neurotransmitters and
depression is complex - more research is needed to
discover the exact biochemical mechanism of the disorder
(Barlow & Durand, 1999).
Hormones People suffering from depression often have high
levels of the hormone Cortisol. Cortisol is sometimes
referred to as a 'stress hormone' because it is produced in
times of stress. The high levels of Cortisol are not surprising
as many depressive episodes are preceded by stressful
events. Given this, the high levels of Cortisol may be a result
rather than a cause of depression - they may be produced
as a response to stress rather than causing the disorder (Ladd
et al., 1996).
Treatment and the biological model
The biological model states that psychological disorders are
caused, at least in part, by biological factors. This suggests
that treatment should address those factors. Many of the
suggested treatments aim to change bodily functioning and
alter biochemical levels.
Drug treatment A range of drug treatments have been
developed which alter the body's biochemistry. For
example, Prozac, an antidepressant drug, increases the level
of the neurotransmitter serotonin. Antidepressants such as
Prozac appear to be effective in 65-75% of cases. This
suggests that depression is, at least in part, due to chemical
imbalances.
However, drugs can have negative side effects. For
example, Prozac, can cause insomnia, headaches and
gastrointestinal disorders. And drugs can lead to physical
addiction, especially if taken in high doses over long
periods of time (Comer, 1998).
Gene therapy The Human Genome Project, which aims to
map the complete genetic makeup of human beings, has
been underway since 1990. However, gene therapy for
genetically based disorders has hardly begun. One day,
individually tailored genetic engineering may liberate those
at risk from inherited disorders.
However, the evidence suggests that genes alone do not
cause psychological disorders. They simply increase the
probability that individuals will develop disorders. The