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 species-
expected 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