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Psychology 304: Brain and Behaviour

Lecture 22

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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?

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1. discuss the mechanisms involved in neuron death.

2. discuss the process and goals of synaptic rearrangement.

By the end of today’s class, you should be able to:

3. discuss neurodevelopment in infancy through to adolescence.

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5. generate examples to illustrate the impact of early experience on neurodevelopment.

4. define the term “sensitive period.”

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5. Neuron death

Large-scale neuron death (i.e., apoptosis) in various parts of the brain is common throughout development and adulthood.

What are the phases of prenatal neurodevelopment? (continued)

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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.”

7Apoptosis

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Following neuron death, some of the synapses formed in earlier stages of development are eliminated

(through retraction of axons) and new synapses are formed.

6. Synapse rearrangement

9Synaptic Rearrangement

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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 ____________.

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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.

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• The prefrontal cortex does not “mature” until lateadolescence.

• The relatively late maturation of this brain region is thought to contribute to the impulsivity observed in early adolescence.

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• The effects of experience on neurodevelopment are often time-dependent.

How does early experience influence neurodevelopment?

• 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

Rats reared in enriched environments.

Children exposed to early music training.

Children with cataracts.

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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?