BIO SCI N110 Lecture 6: 6 Cortical Plasticity in the Developing Visual Cortex
Course CodeBIO SCI N110
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Mon | 5.6.19 Cortical Plasticity in the Developing Visual Cortex
What is cortical plasticity?
Definition and historical background:
• Definition: cortical plasticity is the process by which the developing cortex modifies its own
functional organization following changes in the environment
Historical background (1950s-60s)
• Scientists knew that info from the environment was important for proper brain development
• Kittens raised in the dark become practically blind (not reversible)
• Delaying cataract surgery in babies leads to blindness (but not in adults)
• … but we didn't know why or how that happened
Hubel and Wiesel deprivation experiments and their implications to basic and clinical research
The Eye Deprivation Experiments
• Experimental design
• Hubel and Wiesel tried to create an animal model for amblyopia
• Partial or complete loss of vision from an eye that otherwise appears normal (or
out of proportion given minor structural problems of the eye)
• They closed one eye in kittens (few days old) and waited ~3 months before recording
• A similar experiment was later performed on very young monkeys to confirm the
• Binocular cells: Review from last lecture
• 7 categories of ocular-dominance
• Consequences of closing one eye on V1 cells
• Most of the binocular cells (classes 2-6) become monocular, responding to the "non-
• Not that surprising given the long duration of the deprivation (~3 months)
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• Duration of deprivation is an important factor
Question: where in the visual pathway is the abnormality?
• A: anatomical results showed that the eyes were normal, but that the LGN was abnormal
• LGN layers obtaining input from the deprived eye were paler (less dense) and their cells
Question: could the cat see with the eye that was deprived?
• A: cats could not see from the previously closed eye (but the eye was otherwise normal)
Question: was it light or form deprivation?
• A: it was form deprivation rather than light deprivation
• Fitting an eye with an opaque lens, which transmitted light but no visual pattern, led to
Question: was the age at which the eye was closed important?
• A: age of closure was very important!
• There is a critical (sensitive) period after birth when the deprivation is effective
• There are different durations of critical periods for different animals (e.g. ~4 months in
cats, ~1.5 months in monkey, and ~4-5 years in humans)
• Different parts of the visual system can show different critical periods (e.g., the P system
vs the M system)
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