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Lecture 6

BIO SCI N110 Lecture 6: 6 Cortical Plasticity in the Developing Visual Cortex

Biological Sciences
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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
from V1
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-
deprived" eye
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
were smaller
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
identical results
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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