BIOLOGICAL BASIS
THE DEVELOPMENT OF THE
BRAIN
Dr. Neil H. Schwartz
Lecture 3
Psy 353
TOP HEAVY
• At birth, the human brain weighs 25% of its
eventual adult weight.
• The brain accounts for 10% of the overall body weight of
a newborn.
• However, the infant brain is largely
underdeveloped, only able to perform
basic physiological functions.
• As newborns cannot yet control coordinated movement
nor perform the complex mental operations
characteristic of our species.
NEURONAL
DEVELOPMENT
• The nervous system is a communication system that
uses electrical-chemical signals that are transmitted
from one neuron, or specialized nerve cell, to another.
• There are 10 billion to more than 100 billion neurons in
the mature human brain.
• Each neuron is connected to hundreds to thousands of
other neurons via synapses.
PROLIFERATION,
MIGRATION, AND
DIFFERENTIATION
• Neurons go through three stages of development.
• Proliferation – Occurs during the prenatal period and is
characterized by cell division and mitosis.
• Migration – Once the cells are produced, the cells
move to their permanent location in the brain, where
thy collect with other cells to form the major parts of
the brain.
• Differentiation – Once cells reach their final location,
neurons begin to grow in size, producing more and
longer dendrites, and extending their axons farther from
the cell body.
SYNAPTOGENESIS
AND APOPTOSIS
• Synaptogenesis – Is the process of synapse formation. It
occurs rapidly during the early years of life and
continues throughout life, as the brain changes in
response to new information.
• However, the brain has many more synapses and
neurons than it needs, and the process of synaptic
pruning occurs, apoptosis or selective cell death.
MYELINATION
• Myelin – a fatty substance that surrounds the axons of
neurons and promotes faster transmission of electrical
signals.
• Advantages
• Fire more rapidly
• Lower sensitivity threshold
• Greater functional specificity – “less leakage”
THE ROLE OF EXPERIENCE
IN BRAIN DEVELOPMENT
• Specific experiences produce neural activity that
determine which of the excess synapses will survive.
• Experience-expectant processes – functions will
develop for all members of a species, given a speciestypical environment.
• Those neurons and connections that receive the speciesexpected experience live and become organized with
other activated neurons, and those that do not receive
such activation die. Experience (or lack thereof) changes
structure and organization in the brain.
• Example: visual nervous system development
THE ROLE OF EXPERIENCE
IN BRAIN DEVELOPMENT
• Experience-dependent processes – connections are
made due to the unique experiences that an individual
has.
• Overall, the overproduction of neurons enables an
individual to make connections and store information
that reflects one’s particular environment.
• Therefore, when certain experiences are not
experienced, and these certain neurons are not
activated, then the neurons die.
PLASTICITY
• Plasticity refers to the ability to change.
• Although the brain cannot produce any new neurons,
new synaptic connections can occur throughout life.
• Due to experience
• Through enriched environmental stimulation
• Research suggests that enriched animals have heavier
and thicker neocortexes, larger neurons with more
dendrites, and more synaptic connections.
PLASTICITY
• Brain damage
• Kennard Principle – if one must have brain damage, do
it early, for a young brain is more likely to recover
normal function than an older brain.
• However, when the damage is to an area of the brain
that is involved with more general cognitive functioning
rather than with a specific cognitive ability such as
language, the reverse is often true.
• Drugs