Lecture #6 - Prof. Julie Gros-Louis PDF

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Prof. Julie Gros-Louis...

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PSY:2401:0AAA Lecture #6 Genetics Nervous System, Brain and Behavior 

Stages of nervous system development

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Developmental Processes

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The Importance of Experience

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Brain Damage and Recovery

Six Stages of nervous system development 1. Cell Production (proliferation) ---> neurogenesis 2. Cell Migration ---> neurogenesis 3. Cell Differentiation 4. Synapse Formation ---> synaptogenesis 5. Cell Death 6. Synapse Rearrangement ---> synaptic pruning

Cell Migration 1. Spatial Layering a. New cells push old cells out (old on top of new) b. Or new cells migrate to the outside (new on top of old) 2. Chemical signals 3. Ride the "glial rail" a. Neurons climb up glial rails b. One of the most common ways that cells move

Cell Differentiation 

Depends on: Parent cells

o  o

Where the cells originated Location

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Where they are now Chemical signals

o

Synapse formation (synaptogenesis) 

Cells elongate at their axons to form connections (synapses) with other cells Not actual connections, just close proximity

o 

Each cell forms multiple synapses

Cell Death . . . Why? 

Perhaps a result of cell overproduction o

Not all cells receive nutrients - those that don’t may die

o

Not all cells are active - cells that are not may die

o

Almost like a failsafe, make enough so that if some don’t make the connections that are needed there are plenty to hop in and make that connection

Synapse rearrangement 

2 main types: After cell death, remaining cells make new synapses

o  o

Elongate and spread out Synapses that aren't active are "pruned" (lost)

[copied from Prof. notes]

The BIG Question 

How does the pattern of neural development relate to changes in behavior? To answer this, we need to know a few basics about the brain and how it works…

o 

Cortices/lobes: different lobes serve different functions (though massive interconnections)

o

One proposal: the changes that occur across the 6 stages of neural development provide global constraints on how experience can shape the brain 

Examine changes in grey matter = the "working" tissue in cortex 

Developmental changes in gray matter… 

Early over production followed by pruning (more mature connections)

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BUT this doesn’t happen uniformly across the brain… 

Perceptual and motor areas first to be pruned

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Then areas involved in spatial orientation and language

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Last are areas involved in higher cognition and "executive function"

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Patter of brain maturity is consistent with trends in behavioral development

Experience and the Brain 

Although global constraints are important, brain shows amazing plasticity or flexibility Experience-expectant plasticity

o 

The brain expects normal input so that it can form normal connections

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Is accompanied by vulnerability 

If not available, development will be impaired 

E.g. both eyes typically have similar input during development - if occlude one, do not get typical development

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Sensitive periods 

A key element is timing

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Period when species-typical experience is optimal to achieve species-typical functioning 

o

Timing of occlusion will have differing effects

Experience-dependent plasticity

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[copied from Prof. notes] 

Somatosensory cortex 

Merzenich and Jenkins 

Owl monkeys

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Identified which neurons fired when fingers stimulated

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2 fingers received extra stimulation (1.5 hrs/day for 109 days)

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Competition and selection 

Neurons are very flexible 

Left hemisphere for language, right will be very active and take over if left damaged in childhood

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Experience matters

This is a really good thing!

o

Don’t need to "program" behaviors ahead of time!

o

Brain/child can learn stuff on the fly

Experience and the brain 

Another reason plasticity is good: potential for recovery after brain damage Recovery depends on:

o 

Extent of the damage

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Aspect of brain damage developing at time of damage

o

Timing of damage critical 

"worst time" is during prenatal development (neurogenesis and neural migration)

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"best time" is during infancy and early childhood (synapse generation and pruning)...