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64 Cards in this Set

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What is a deprivation experiment?
Where you deprive the nervous system of a stimuli and see what deficits develop.
What is Amblyopia?
A partial or complete loss of eyesight that is not caused by abnormalities of the eye.
What causes amblyopia if it is not an abnormality of the eye?
Abnormal visual experiences during development.
What is necessary for the correct and proper development of the nervous system?
Neural plasticity
What happens to the degree of plasticity as we develop?
It decreases
When does visual plasticity become depleted so that circuits are unchangeable
9 years old
What is Amblyopia?
Partial or complete loss of eyesight that is not due to an eye abnormality.
What can cause Amblyopia?
Abnormal visual experience during development.
What is a type of abnormal visual experience?
Complete visual deprivation obviously.
If someone who has been blind from birth is given an operation and suddenly they can see again, is that true?
No
Even if surgery could restore vision, would a person who had been blind from birth be able to see?
No
Why not?
Because you need the visual experience in order to develop the brain for vision.
What is the exception to this rule?
If vision loss occurred later in life - then there is the brain for it to be restored.
What is a monocular neuron?
One whose activity can be influenced ONLY by stimulation of one of the eyes
What are the 3 places where there are monocular neurons in the brain?
-Retina
-LGN
-Layer 4C of V1
What is a binocular neuron?
One whose activity can be influenced by stimulation of either eye.
What are binocular neurons in the cortex important for?
Integrating information from the 2 eyes to make a single 3D perception.
Where are the binocular neurons found?
In V1 cortex - primary visual
Do binocular cells in V1 cortex respond equally well to both eyes?
No, some are more responsive to stimulation of one eye over the other.
What is that called?
Ocular dominance
If a kitten's right eye is deprived from light for 2.5 months and then light is shone in the left eye, what cells will respond?
only monocular - not binocular; and only the monocular cells that respond to lite in the left eye.
What if that same kitten is not deprived of light, by putting a foggy contact lense on its eye?
It still won't develop binocular neurons or right monocular neurons.
What if it just has pattern deprivation?
Same results
What are "critical periods" in visual development?
The periods where abnormal visual experiences will permanently affect vision.
What is the GOOD thing about Critical periods?
If abnormal visual experiences occur AFTER them they won't cause a marked effect!
What is the result of depriving the eye of vision for 6 weeks, starting at 5 days old?
A marked shift in ocular dominance
What is the result of closing the eyes for a few days at the age of a few weeks old?
A marked shift in ocular dominance
What is the effect of closing the eyes for 5 years at the age of 4 months (which is equivalent to a 5yr old child)?
Little effect!
What do we conclude?
There is a critical period for eye development.
If an eye is covered for 9 days from birth and tested 4 years later will there be any reversal of the induced amblyopia?
No
If an eye is deprived for 5.5 weeks and then reversed for 6 months by patching the GOOD eye, will the amblyopic eye recover?
YES!
If an eye is deprived from birth for a year, then the deprival is reversed to the good eye, will the amblyopic eye recover?
NO - waited past the critical period.
So how can amblyopia be treated?
By reversal at the correct point in development, for the appropriate amount of time, and under a dr's watch
Why is it that you can't reverse amblyopia after the critical period?
Because all the neurons in the LGN that are responsible for giving input from the deprived eye DIE when not stimulated.
What is the most common cause of amblyopia?
Strabismus
What does Strabismus mean?
Nonparallel eyes; cross-eyes or wall-eyes
What are some causes of strabismus?
-Eye muscle abnormality
-Abnormal brainstem circuits that control eye movements
-Farsightedness
What are the 3 things that are involved in accomodation (near sightedness)?
1. Constrict pupils
2. Convergance
3. Ciliary muscle contraction
How can far sightedness cause amblyopia?
A farsighted person cannot accommodate correctly, so the out of focus image is read by the brain, which activates the eyes to keep converging - leads to strabismus.
What is the result of being cross-eyed (strabismus)?
Double vision
What does the brain have to do when a person is crosseyed?
Compensate for the double vision so the person can still function.
What are the 2 strategies for compensation of strabismus?
1. Alternation
2. Suppression
What is alternation?
Trading off between the eyes
What will vision testing in that person show if each eye is tested individually?
Normal!
But 3D vision is not normal.
What is Suppression? What does this technique of compensation result in?
The brain picks one eye and continuously suppresses the image from the other eye; results in blindness in the other eye
What should I remember about Suppression compensation for strabismus?
That it is one of the most common causes of visual loss!!!
How did investigators investigate strabismus in an animal model?
By cutting ocular muscles in kittens
What type of strategy do kittens tend to use for strabismus?
Alternating - use one eye/suppress one, then switch.
What is the vision in each eye used during alternation like?
Normal
What happens to most ocular neurons in the upper layers of V1 cortex as a consequence of strabismus?
They become monocular
So where is the change that causes strabismus?
In the CORTEX - NOT the eyes.
What do the cortical changes in strabismus have to do with?
The relationship between the stimuli in the two eyes.
What is Stripe rearing?
Exposing animals to only a certain orientation of stripes during development and changing the way their cortexes work.
What are 5 eye abnormalities that MUST be corrected early?
1. Cross eye
2. Cataracts
3. Corneal opacity
4. Differences in the refractive error between the 2 eyes
When wouldn't you treat these diseases?
In adults - it won't change much.
What is Hebb's model of a mechanism for neural plasticity?
Cooperation
What does Hebb's model of cooperation say?
That if Neuron A fires on Neuron C, the firing will strengthen their synapse.
What if neuron B fires on Neuron C as well?
That will strengthen the A-C connection too
What does Neuron B's strengthening of the A-C synapse mean will happen if Neuron B DOESN'T fire?
Then A-C might not be strong enough.
How does the cooperation model help us understand binocular neurons?
When one eye is deprived, the connection between the brain and the opposite eye makes the neuron only monocular instead of binocular
So how does amblyopia develop based on Hebb's model?
All the neurons become monocular for one eye and crowd out the other eye.
What does the competition model of a mechanism for neural plasticity show?
That the later you deprive an eye, the less competition is remaining in the visual cortex, so neurons in the deprived eye will persist.
What are 3 ways that appropriate connectings are made in the developing nervous system?
1. Genetic specification
2. Guided by experience
3. By random chance
What does genetic specification mean?
There is a complicated mechanism that tells axons from the ganglion cells to go to the LGN.