Invitation to Psychology

Chapter 11 Psychological Disorders 409

an environmental stressor to trigger the disease.

This model explains why one identical twin may

develop schizophrenia but not the other: Both

may have a genetic susceptibility, but only one

may have been exposed to other risk factors in the

womb, birth complications, or stressful life events.

winter month, and a very low birth weight (King,

St-Hilaire, & Heidkamp, 2010).

3

Biological events during adolescence. In ado-

lescence, the brain undergoes a natural prun-

ing away of synapses. Normally, this pruning

helps make the brain more efficient in handling

the new challenges of adulthood (Walker &

Tessner, 2008). But it appears that in schizophre-

nia, the brain aggressively prunes away too many

synapses, which may explain why the first full-

blown schizophrenic episode typically occurs in

adolescence or early adulthood. Healthy teen-

agers lose about 1 percent of the brain’s gray

matter between ages 13 and 18. But as you can

see in Figure 11.5, in a study that tracked the

loss of gray matter in the brain over 5 years,

adolescents with schizophrenia showed much

more extensive and rapid tissue loss, primarily

in the sensory and motor regions (Thompson et

al., 2001). “We were stunned to see a spreading

wave of tissue loss that began in a small region

of the brain,” said Paul Thompson, who headed

the study. “It moved across the brain like a for-

est fire, destroying more tissue as the disease

progressed.”

Thus, the developmental pathway of schizo-

phrenia is something of a relay. It starts with

genetic predispositions, which may combine with

prenatal risk factors or birth complications that

affect brain development. The resulting vulner-

ability then awaits the next stage, synaptic pruning

within the brain during adolescence. Then, accord-

ing to the vulnerability-stress model of schizo-

phrenia, these biological changes may interact with

10

Lifetime risk of developing schizophrenia

0

Unrelated person in

the general population

20 30 40 50 60

Child of one

schizophrenic parent

Child of two

schizophrenic parents

Identical twin

Fraternal twin

Sibling

FigURE 11.4 genetic Vulnerability to Schizophrenia

This graph, based on combined data from 40 European twin and adoption studies conducted over seven decades,

shows that the closer the genetic relationship to a person with schizophrenia, the higher the risk of developing the

disorder. (Based on Gottesman, 1991; see also Gottesman et al., 2010.)

FigURE 11.5 The Adolescent Brain

and Schizophrenia

These dramatic images highlight areas of brain-tissue

loss in adolescents with schizophrenia, over a five-year

span. The areas of greatest tissue loss (in regions that

control memory, hearing, motor functions, and attention)

are shown in red and magenta. The brain of a person

without schizophrenia (top) looks almost entirely blue

(Dr. Arthur W. Toga, Laboratory of Neuro Imaging, UCLA

School of Medicine).