Understanding Psychology (10th Ed)

SOLVING THE PUZZLE OF SCHIZOPHRENIA: BIOLOGICAL CAUSES 
Although schizophrenic behavior clearly departs radically from normal behavior, its 
causes are less apparent. It does appear, however, that schizophrenia has both bio-
logical and environmental origins (Sawa & Snyder, 2002). 
Let’s fi rst consider the evidence pointing to a biological cause. Because schizo-
phrenia is more common in some families than in others, genetic factors seem to 
FIGURE 8 
This unusual art was created by an individual suff ering from severe mental 
disturbance.
Study Alert
In Type I schizophrenia, posi-
tive symptoms (in which 
hallucinations, delusions, 
and emotional extremes 
are present) are dominant; 
in Type II schizophrenia, negative 
symptoms (characterized by an 
absence or loss of normal functioning) 
are dominant.
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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).