Chapter 4 Neurons, Hormones, and the Brain 143are said to have hardwired brain differences that
explain, among other things, women’s allegedly
superior intuition and empathy, women’s love of
talking about feelings and men’s love of talking
about sports, women’s greater verbal ability, men’s
greater math ability, and why men won’t ask for
directions when they’re lost.
What are we to make of these arguments,
which are often presented with lots of fMRI images
and other pictures of the brain? Unfortunately,
ideology can get in the way of the answer. Some
people worry that the research can be used to jus-
tify sexist practices and discrimination, a legitimate
concern. Others argue, just as legitimately, that
ignoring the evidence is antiscientific and an im-
pediment to improving the lives and health of both
women and men (Saletan, 2011).
To evaluate this issue intelligently, we need
to ask two separate questions: Do the brains of
males and females differ, on average, in structure
or function? And if so, what, if anything, do the
differences have to do with men’s and women’s
behavior, abilities, ways of solving problems, or
anything else that matters in real life?
The answer to the first question is yes: Many
anatomical and biochemical sex differences have
been found in animal and human brains (Cahill,
2005; Luders et al., 2004). Some of these differ-
ences appear to be universal. An international
study combined fMRI data from 24 laboratories
and more than 1,000 people in seven countries,
from Australia to China to Finland. In every
country, men and women showed different pat-
terns of activity across the brain as a whole, even
when their brains were not doing mental work.
People of all ages, both sexes, and from all cultures
showed remarkably similar patterns of connectiv-
ity between particular brain regions, but there
were also some significant differences between
the patterns seen in men and women (Biswal
et al., 2010).
In addition, parts of the frontal lobes are
larger in women, relative to the overall size of
their brains, whereas parts of the parietal cortex
and the amygdala are larger in men (Goldstein
et al., 2001; Gur et al., 2002). Women also have
more cortical folds in the frontal and parietal
lobes (Luders et al., 2004). On average, men have
more cortical neurons than women do, and some
researchers speculate that this difference contrib-
utes to a sex difference in spatial abilities, such as
skill at mentally rotating objects (Burgaleta et al.,
2012). Finally, in men, the right amygdala keeps
getting input from the rest of the brain; in women,
the left amygdala gets that input. This difference
may predispose men and women to encode and
remember emotional information differently. In
men, better memory is associated with greaternot only between the ears and the auditory cortex
but also between the ears and the visual cortex.
Typically, experience strengthens the connections
between the eyes and the visual cortex, and be-
tween the ears and the auditory cortex, and prunes
away the other two types (Innocenti & Price, 2005).
The intriguing question, therefore, is what happens
in the visual cortex of blind people? Is it able to
respond to sound because it is not receiving sights?
To answer this question, researchers used PET
scans to examine the brains of people as they local-
ized sounds heard through speakers (Gougoux et
al., 2005). Some of these people were sighted and
others had been blind from their early years. When
they heard sounds through both ears, activity in
the occipital cortex, an area associated with vision,
decreased in the sighted people but not in the blind
ones. When one ear was plugged, the blind people
who did especially well at localizing sounds showed
activation in two areas of the occipital cortex; nei-
ther sighted people nor blind people with ordinary
ability showed that activation. What’s more, the
degree of activation in these regions was correlated
with the blind people’s accuracy on the task. The
brains of those with the best performance had ap-
parently adapted to blindness by recruiting visual
areas to take part in activities involving hearing—a
dramatic example of plasticity.
Conversely, when sighted people were blind-
folded for five days, their brains adapted to their
inability to see by temporarily recruiting visual
areas for tasks requiring hearing or touch (Pascual-
Leone et al., 2005). The visual areas of the brain
apparently possess the machinery necessary for
processing nonvisual information, but this machin-
ery remains dormant until circumstances require
its activation (Amedi et al., 2005). When people
have been blind for most of their lives, instead of
just five days, new connections may form, permit-
ting lasting structural changes in the brain’s wiring.
This research teaches us that the brain is a
dynamic organ: Its circuits are continually being
modified in response to information, challenges, and
changes in the environment. As scientists come to
understand this process better, they may be able to
apply their knowledge by designing improved reha-
bilitation programs for people with sensory impair-
ments, developmental disabilities, and brain injuries.
Watch the Video Special Topics:
The Plastic Brain at mypsychlabare There “His” and “Hers”
Brains? Lo 4.16
Many bestselling books have claimed that the “fe-
male brain” and the “male brain” are as dissimilar
as tomatoes and artichokes. Males and females