-Newborns spend half of their sleeping hours in active sleep, also called REM
sleep (for the rapid eye movements that occur during it).
-Infants older than 6 months spend only 2530% of their total sleep in REM
sleep, which more closely resembl
-Primitive reflexes typically disappear during the early months of infancy.
-For instance, the grasping reflex becomes weak by 4 months and is replaced by
voluntary grasping. These primitive reflexes are controlled by the lower,
subcortical areas o
-In the past, we might have answered that the brain was fully developed by the
end of infancy, or even by the end of pregnancy.
-Today, however, the answer is that brain development is never truly complete.
The brain is responsive to experien
-As the nerves and muscles mature downward and outward, infants gradually
gain control over the lower and the peripheral parts of their bodies.
-The orthogenetic principle is also evident in early motor development.
-A young infant is likely to
-Although neurons come in many shapes and sizes, they have some common
features. Branching, bushy dendrites receive signals from other neurons, and the
long axon of a neuron transmits electrical signals to other neurons or, in some
-Boys larger musculature may give them an advantage over girls in activities that
-But larger muscles cannot ex- plain why girls are less active. Gender-role
socialization may be partly responsible.
-As girls mature sexually a
-Treatment with synthetic growth hormones can lead to near-expected adult
height if administered earlywell before the start of puberty
Children born small for their gestational age are often shorter as adults.
-Some of these children may a
-One important feature of the developing organization of the brain is the
lateralization, or asymmetry and specialization of functions, of the two
hemispheres of the cerebral cortex.
-Instead of developing identically, the functions control
Growth in Adolescence
-Thelen showed that it simply requires more strength to make the walking motion
standing up (as in the stepping reflex) than to make it lying down (as in kicking).
She demonstrated that babies who no longer showed the stepping motion
-Human growth and development is an incredibly complex process, influenced by
both genetic and environmental factors.
-If you lack adequate nutrition, for example, you may not realize your full growth
-And con- sider the case of ch
Genetics and Brain Behavior
-But genes are not the only influence an individuals experiences are also
crucial to brain development.
-Thus, the brain, especially early in its formation, has great plasticity; that is, it is
responsive to the individuals exp
-Estrogen increases dramatically at puberty, stimulating the production of growth
hormone and the adolescent growth spurt, much as testosterone does in males.
-It is also responsible for the development of the breasts, pubic hair, and fem