Roger Sperry`s Classic Experiment (1940`s)

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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
tectum
retina
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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 p
mechanical trails that growing axons follow to their destinations.
Pioneer axons
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
The remaining ones systematically project over the entire tectum.
Optic tectum
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If one lesions 1/2 the tectum & nerve cut...
retina
The retinal ganglion cells projected systematically over the remaining half tectum.
Optic 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 2005
February 2
Minds and Brains, Winter 2005
February 2
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Minds and Brains, Winter 2005
February 2
The case of Tom and Philip...
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