Why Testosterone is Essential for Engineering a Male Brain 207
in shaping brain morphology, evidence also suggests that fetal testosterone
and the AR are important in shaping male behavior, both during its early
organization and its later activation in adulthood. Although aromatization
may account for many sex differences in behavior, research suggests that tes
tosterone and ARs play a critical role in a variety of behaviors ranging from
sexual to cognitive. These include spatial memory and anxiety‐related behavior.
Spatial Memory
In general, human males outperform females in spatial memory performance.
These gender differences have been ascribed to the organizational effects of
testosterone, since neonatal castration of males or administration of testoster
one to newborn females eliminates this observed sex difference. This also fits
into the “extreme male brain” hypothesis we have detailed in Chapter 5. The
biochemical conversion of testosterone to estrogens (called aromatization)
may be particularly important in the development of the sex difference, since
neonatal administration of estrogen masculinizes spatial ability in female rats.
However, this may not be the only mechanism. In fact, other evidence suggests
that perinatal AR expression during early stages of gestation activation may
also play a role in enhancing male spatial memory performance. Isgor and
Sengelaub [120] found that prenatal estrogen treatment did not masculinize
performance, whereas treatment with testosterone did. In addition, in experi
mental animals, males administered AR antagonists prenatally showed poorer
performance than control males, eliminating the sex difference in this behav
ior, play fighting and aggression, and sexual/social behavior.
Anxiety‐Related Behavior
Anxiety is a psychological, physiological, and behavioral state induced in
animals and humans by a threat to well‐being or survival, either actual or
potential. It is characterized by increased arousal, expectancy, autonomic and
neuroendocrine activation, and specific behavior patterns. The function of
anxiety‐related behavior is to facilitate coping with an adverse or unexpected
situation. Pathological anxiety interferes with the ability to cope successfully
with normal life tasks. Anxiety‐related behavior appears to be a result of
predisposing factors, including gene–environment interactions during the
early developmental period as well as life events. In humans, anxiety disorders
are estimated to affect about 1 in 5 people and there are striking sex differences
in the prevalence of these disorders.
Social anxiety disorders are more prevalent in women than men and women
tend to receive the majority of diagnoses for specific phobias (e.g., panic
disorder, post‐traumatic stress disorder, fear of spiders, fear of heights, etc.).
Differences in circulating sex hormones, estrogen and testosterone, are likely
