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Psychology 304:
Brain and Behaviour
Lecture 22
1
Development of the Nervous System
1. What are the phases of prenatal neurodevelopment?
(continued)
2. What developmental changes are observed in the
nervous system after birth?
3. How does early experience influence
neurodevelopment?
2
By the end of today’s class, you should be able to:
1. discuss the mechanisms involved in neuron death.
2. discuss the process and goals of synaptic
rearrangement.
3. discuss neurodevelopment in infancy through to
adolescence.
3
4. define the term “sensitive period.”
5. generate examples to illustrate the impact of early
experience on neurodevelopment.
4
What are the phases of prenatal neurodevelopment?
(continued)
5. Neuron death
 Large-scale neuron death (i.e., apoptosis) in various
parts of the brain is common throughout development
and adulthood.
5
 Neurons compete for connections to target organs.
Those neurons that form connections are exposed to
life-preserving chemicals called neurotrophins.
 The most well-studied neurotrophin is nerve growth
factor.
 Neuron death is an active process. The absence of
neurotrophins triggers a genetic program that causes
the neuron to “commit suicide.”
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Apoptosis
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6. Synapse rearrangement
 Following neuron death, some of the synapses
formed in earlier stages of development are eliminated
(through retraction of axons) and new synapses are
formed.
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Synaptic Rearrangement
9
Self-Test
Complete the following list of the chronological stages of
neurodevelopment.
1. Induction of the neural ____________.
2. Formation of the ____________ tube.
3. Cell ____________.
4. Cell ____________.
5. Growth of ____________.
6. Formation of ____________.
7. Neuron ____________ and synapse ____________.
10
What developmental changes are observed in the
nervous system after birth?
• With two exceptions, all of the neurons that will
compose the adult human brain develop by the 7th
month of pregnancy.
• Nevertheless, the brain grows substantially after birth.
• Postnatal brain growth results from synaptogenesis,
myelination of axons, and increased branching of
dendrites.
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• The rates of postnatal synaptogenesis and myelination
vary across brain regions.
• Once maximum postnatal synaptic density is achieved,
synaptic loss often occurs.
• The overproduction of synapses early in life is
thought to underlie the greater plasticity of the child’s
brain.
12
• The prefrontal cortex does not “mature” until late
adolescence.
• The relatively late maturation of this brain region is
thought to contribute to the impulsivity observed in early
adolescence.
13
How does early experience influence neurodevelopment?
• The effects of experience on neurodevelopment are
often time-dependent.
• Sensitive period: A period during which an organism is
highly responsive or sensitive to environmental
influences; a “window of opportunity” for experience to
markedly influence development.
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• Research on the effects of experience on
neurodevelopment has largely focused on sensory and
motor systems. This research has examined the impact
of sensory deprivation and sensory enrichment.
• Examples:
 Monocular and binocular deprivation in cats
 Children with cataracts.
 Rats reared in enriched environments.
 Children exposed to early music training.
15
Development of the Nervous System
1. What are the phases of prenatal neurodevelopment?
(continued)
2. What developmental changes are observed in the
nervous system after birth?
3. How does early experience influence
neurodevelopment?
16