that there is a reduction in the plasticity of these circuits after a sensi-
tive period has ended.
There are parts of the brain that are capable of continuing renewal
and development in normal circumstances. One region of the brain
that has been extensively studied in respect to renewal is the hip-
pocampus, which is important in respect to memory.
In a detailed analysis of neurons and their connections, it was
found that, at birth, the axons, dendrites, and synapses in the brain
are not extensive, but at the age of 6 years, the neuron connections
and synapses are extensive. By age 14 years, the synapses are less
extensive.
The connections between neurons are strongly influenced by stim-
ulation. Hebb (1949) referred to this process of the wiring and sculpt-
ing of the brain as “neurons that fire together, wire together.” The
formation of long-lasting synaptic connections is dependent upon
the frequency of the stimulation of the receiving neuron. Frequent
stimulation leads to activation of genetic pathways in the brain
which produce proteins that strengthen synapses.
The LHPA (Stress) Pathway
The LHPA pathway has major effects on physical and mental health.
In discussing the stress response, two terms are often used—the limbic
system, and the hypothalamus-pituitary-adrenal (HPA) pathway or
axis.
The term limbic system was originally used to relate to the center
for emotions. Since the concept was introduced, there is evidence
that two structures in the limbic system of the brain (hippocampus
and amygdala) play important roles in emotion, behavior, and mem-
ory and are inseparable from the stress response. The stress pathway
is considered by many to involve the limbic system and includes the
amygdala, the hypothalamus, the pituitary gland, the adrenal gland,
and the hippocampus. The stress pathway also involves the auto-
nomic nervous system.
One set of nerves projecting from the amygdala reaches parts of
the midbrain and brain stem which control the autonomic nervous
Scientific Underpinnings of the Importance of ECD in a Global World 51