32 Part One Children in Today’s World
Heredity and
Environment Interact
Scientists now know that
heredity and environment work
together to develop the brain.
Heredity affects how many neurons
a baby will have throughout life.
All these neurons will be present at
birth. In addition, half of a person’s
80,000 genes are involved in brain
growth and development. These
genes cause cells to divide and
grow. They are also responsible
for basic wiring between the axons
and dendrites before birth. When
the baby is born, he or she will
have about 50 trillion synapses in
the brain. These synapses are the
ones the baby must have to survive
outside the mother’s body.
Unlike a computer that is built
and then turned on, the brain starts
working even before it is fi nished.
The basics are present at birth, but
the baby’s brain continues to grow
after birth. When stimulated, the
axon sends electrical impulses to
the dendrites of other cells. These
messages help the brain form more
synapses (connections) between
the neurons. Repeating a positive
experience causes the impulses to
be sent again, which strengthens
the connection.
The brain can use a stronger
connection more easily than a weak
one. Over time, the brain continues
to strengthen used pathways, but
begins to weed out the unused
pathways. This process is called
pruning. Healthy pruning allows
the remaining connections to
become strong. This increases the
speed and effi ciency for often-used
brain signals. Too much pruning
means the person will not be able to
develop certain needed skills and
abilities. Pruning begins in the very
fi rst years of a child’s life and is
almost completed by age 10 years.
In this system of wiring,
the environment is crucial. Rich
sensory experiences create new
dendrites, which build new networks
for learning. Examples of rich
experiences are getting a hug, hearing
music, learning a skill, and exploring
a toy. In the fi rst year of life, the
number of synapses increases to more
than 1,000 trillion. This allows for the
rapid rate of learning among babies
and young children.
Windows of
Opportunity
Timing is an important concept
when it comes to brain development.
The entire brain is not wired at one
time. Genes control the general
order and timetable in which regions
of the brain develop. Each region
has a specifi c function, such as
processing a person’s movement,
language, memory, emotions, or
Brain Development
Rich sensory experiences strengthen and
refi ne the brain’s wiring. A lack of stimulation
can prevent some connections from forming
and cause pruning to other connections. In fact,
early experiences have such a dramatic effect
on brain wiring they can increase or decrease
the fi nal number of synapses by as much as
25 percent. The effects this has on future learning
potential are lifelong. What does this say about
the importance of caring for babies and young
children? What effects can effective caregiving
have on the future of your community,
country, and the world? What results
might ineffective caregiving have?