roger sperry’s classic experiment...
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Roger Sperry’s Classic Experiment (1940’s)
Frog behavior: Dangle a lure frog will grab it with its tongue.
Roger Sperry’s Classic Experiment (1940’s)
Frog visual system
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Minds and Brains, Winter 2005 January 28, 2005
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How do neurons know were to go??? Roger Sperry (1963)
Chemoaffinity Hypothesis:
Postsynaptic surface has chemical tags that direct the neuron to its proper location
In vitro experiments
retina
tectum
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It does not account for...targets transplanted to novel positions sometimes innervate the incorrect target.
Some axons follow the same circuitous route to their target in every member of a species, rather than growing directly to the target.
Not enough genes to account for a different chemical tag for every neuron to reach its proper location.
Blue Print Hypothesis...
The undeveloped nervous system contains specific chemical or
Pioneer axons
pmechanical trails that growing axons follow to their destinations.
Experiment: Pioneer axons in fish destroyed, subsequent axons of the same nerve never made it to their target.
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Chick Spinal Cord: Muscle Innervation
???
Topographic Gradient Hypothesis
retina tectum
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retina
Optic tectum
If one lesions 1/2 the retina & nerve...retina
Optic tectumThe remaining ones systematically project over the entire tectum.
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If one lesions 1/2 the tectum & nerve cut...
retina
Optic tectumThe retinal ganglion cells projected systematically over the remaining half tectum.
Diffuse pattern of synaptic contact
Early stages of development
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Focused pattern of synaptic contact
After synapse rearrangement has occurred
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What happens when...
Mechanisms of neural reorganization...
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Minds and Brains, Winter 2005February 2
Minds and Brains, Winter 2005February 2
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Minds and Brains, Winter 2005February 2
The case of Tom and Philip...
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