Invitation to Psychology

142 Chapter 4 Neurons, Hormones, and the Brain

letters and sounds (Tang et al., 2006). In the words

of one researcher, “Much like the changing tide can

erode a footprint in the sand, so too can changed ex-

perience over time reshape brain activations. In this

sense, the brain can be seen as a ‘cultural sponge’ of

sorts, absorbing the regularities of our surrounding

physical and social environments” (Ambady, 2011).

Plasticity is especially dramatic in cases of

people with brain damage who have experienced

remarkable recoveries—such as individuals who

cannot recall simple words after a stroke but are

speaking normally within months, or who cannot

move an arm after a head injury but regain full use

of the limb after physical therapy. Their brains

have apparently rewired themselves to adapt to

the damage (Liepert et al., 2000).

Plasticity is also apparent in some people who

have been blind or deaf from birth or early child-

hood. In the period of rapid development after

birth, connections form not only between the eyes

and the visual cortex but also between the eyes and

the auditory cortex. Likewise, connections form

You are about to learn...

•    why the brain is considered to be “plastic.”

•    some findings and fallacies about sex

Psychology in the News

the Flexible Brain

Many people think of the brain as if it were some

fixed and unchanging organ, the same in everyone

and essentially the same at birth as at age 8, 18,

28, or 98. It is true that because we are all human

and most of us share common early experiences—

learning to talk, walk, deal with school and with

family members—our brains are fundamentally

similar in their basic organization. Yet we also

have differing experiences as a result of grow-

ing up rich or poor, male or female, nurtured or

neglected, and these experiences occur within a

particular culture that shapes our values, skills,

and opportunities. Such differences can affect the

brain’s wiring and how it is used.

experience and the Brain Lo 4.15

Our brains are not fully formed at birth. During

infancy, synapses proliferate at a great rate (see

Figure 4.12). Neurons sprout new dendrites, cre-

ating not just new synapses but also more com-

plex connections among the brain’s nerve cells

(Diamond, 1993; Greenough & Anderson, 1991;

Greenough & Black, 1992; Rosenzweig, 1984).

New learning and stimulating environments pro-

mote this increased complexity. Then, during

childhood, synaptic connections that are useful for

helping the child respond to the environment are

strengthened, whereas those that are not useful

wither away, leaving a more efficient neural net-

work. In this way, each brain becomes optimized

for its environment. This plasticity, the brain’s

ability to change in response to new experiences,

is most pronounced in infancy and early child-

hood, but it has a resurgence in adolescence and

continues throughout life, even into old age.

Many of the experiences that affect us—and

our brains—depend on the culture we live in, as

children and adults. When two cultures value

different skills among their members, when they

emphasize different approaches to acquiring com-

mon skills, or when they encourage bilingualism,

people’s brains may reflect those differences. The

patterns of brain activity during mathematical pro-

cessing are different in native Chinese speakers than

in native  English speakers. Both groups can learn

that 2 + 2 = 4, but their brains will take different

routes to get there, because of the different ways

that the Chinese and English languages process

plasticity The brain’s
ability to change and
adapt in response to
experience, by reorganiz-
ing or growing new neural
connections.

At birth3 months

6 months 15 months

Figure 4.12 getting Connected

Neurons in a newborn’s brain are widely spaced, but

they immediately begin to form new connections. These

drawings show the marked increase in the number of

connections from birth to age 15 months.