Module 47
The Major Psychological Disorders
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be involved in producing at least a susceptibility to or readiness for developing
schizophrenia. For example, the closer the genetic link between a person with
schizophrenia
and another individual, the greater the likelihood that the other per-
son will experience the disorder (see Figure 9 ; Brzustowicz et al., 2000; Plomin &
McGuffi n, 2003; Gottesman & Hanson, 2005).
However, if genetics alone were responsible for schizophrenia, the chance of both
of two identical twins having schizophrenia would be 100% instead of just under
50% because identical twins have the same genetic makeup. Moreover,
attempts to
fi nd a link between schizophrenia and a particular gene have been only partly suc-
cessful. Apparently, genetic factors alone do not produce schizophrenia (Franzek &
Beckmann, 1996; Lenzenweger & Dworkin, 1998).
One intriguing biological hypothesis to explain schizophrenia is that the brains
of people with the disorder may harbor either a biochemical imbalance or a structural
abnormality. For example, the
dopamine hypothesis suggests
that schizophrenia occurs
when there is excess activity in the areas of the brain that use dopamine as a neu-
rotransmitter. This hypothesis came to light after the discovery that drugs that block
dopamine action in brain pathways can be highly effective in reducing the symptoms
of schizophrenia. Other research suggests that glutamate, another neurotransmitter,
may be a major contributor to the disorder (Ohara, 2007; Stone,
Morrison, & Pilowsky,
2007; Howes & Kapur, 2009).
Some biological explanations propose that structural abnormalities exist in the
brains of people with schizophrenia perhaps as a result of exposure to a virus during
prenatal development. For example, some research shows abnormalities in the neural
circuits of the cortex and limbic systems of individuals with schizophrenia. Consis-
tent
with such research, people with schizophrenia and those without the disorder
show different brain functioning (see Figure 10 ; Bartzokis et al., 2003; Reichenberg &
Harvey, 2007; Reichenberg et al., 2009).
Further evidence for the importance of biological factors shows that when people
with schizophrenia hear voices during hallucinations, the parts of the brain respon-
sible for hearing and language processing become active. When they have visual
hallucinations, the parts of the brain involved in movement and color are active. At
the
same time, people with schizophrenia often have unusually low activity in the
brain’s frontal lobes—the parts of the brain involved with emotional regulation,
insight, and the evaluation of sensory stimuli (Stern & Silbersweig, 2001).
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