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Psychology 304: Brain and Behaviour

Lecture 18

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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?

Synapse formation occurs once axons and dendrites have reached their target locations.

Astrocytes are involved in the formation of synapses.

Synapses that do not function properly after formation are typically eliminated.

What are the phases of prenatal neurodevelopment? (continued)

4. Axon growth and synaptogenesis (continued)

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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.

Neurons compete for connections to target organs. Those neurons that form connections are exposed to life-preserving chemicals referred to as

neurotrophins.

The most well-studied neurotrophin is nerve growth factor.

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Neuron death is an active process. The absence of neurotrophins triggers a genetic program that causes the neuron to “commit suicide.”

6Apoptosis

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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

8Synaptic Rearrangement

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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 have developed 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.

• 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 enviroments.

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?