Central Visual Processing II Lec13 Flashcards
Synaptic plasticity is the ability of a
synapse between two neurons to
change in ___ or ___
strength or effectiveness.
. Input from the LGN into V1 maintain ___ segregation and setup the OD columns in V1
monocular
Visual deprivation and
competition study
1 is a cell
that is completely dominated by ____ eye
input
contralateral
Visual deprivation and
competition study
, 7 is dominated by the ___ eye
ipsilateral
Visual deprivation and
competition study
__
is a binocular cell equally driven by either eye.
4
Visual deprivation and
competition
In the normal adult primate, how many 1,7,4s are there?
equal numbers of cells driven by each eye (i.e. the
numbers of cells with OD=1,2,3 about equal cells
with OD=5,6,7),
Experiment: monocular deprivation (MD)
- One eyelid is sutured soon after birth and it
remains closed for 6 months
after opening eyelid
what was the distribution of the OD scale?
all were either 1s or 7s meaning
t nearly all cells are driven by the eye that wasn’t
sutured close
Experiment: monocular deprivation (MD)
- One eyelid is sutured soon after birth and it
remains closed for 6 months and then open
all cells designated 1s and 7s
was this change permanent?
yes
Experiment: monocular deprivation (MD)
- One eyelid is sutured soon after birth and it
remains closed for 6 months and then open
all cells designated 1s and 7s
where in the brain were there changes?
in V1 itself, not in the retina, because
the eye, retina, LGN, optic radiations, etc were found
all to be normal.
what condition resutls from monocular deprivation
(all cells driven by eye that wasn’t sutured closed?)
amblyopia.
Intravitreal injection in one eye, of 3H-proline in a v1 monocular deprived and a v1 normal monkey
what changes were noticed in the cortex?
- Under monocular deprivation, the “good” eye (non-deprived) has taken over the territory normally
occupied by the other (occluded, deprived) eye
Normal OD columns exhibit a roughly equal ___ of
bands for each of the two eyes
width
Normal OD columns exhibit a roughly equal width of
bands for each of the two eyes, whereas in monocular deprivation, the deprived eye bands are much
___
thinner
critical period in humans
birth and 6-8 years
s (in a kitten, 6 months in a monkey, 6-8 years in a
human child).
A few ___ of deprivation
can permanently altered the development of the OD
columns during the critical period
days
The effects of a brief period of monocular deprivation
may be partially reversed if,
during critical period
- sutured eye is opened
- nonsutured eye is sutured
* allows it to regain its cortical territory
- Binocular deprivation (BD) during the critical period
seems to ___ the critical period somewhat
lengthen
- The binocular deprivation experiments show that the
effects of MD are not simply the result of “disuse”, but
instead indicate an
active competition
strabismus, as a
___ disorder
peripheral
amblyopia, as a ___
disorder.
central
Strabismus invovles the
extracocualr muscles
strabismus is caused by a a misalignment of the two
eyes preventing
proper binocular vision
what can strbismus lead to if occuring in the young
ambylopia
Amblyopia: (lazy eye), a central disorder resulting from
an imbalance or lack of visual coordination between the
two eyes during development
Amblyopia deficits include
poor vision or acuity in one eye
compared to the stronger eye
causes of Amblyopia: include
- strabismus
- refractive errors
- cataracts
Amblyopia is Characterized
by an abnormal development of connections in the ___
visual cortex
what eye does a patch go on in ambyopia? what can be a side effect?
on good eye
can cause poor bionuclar depth (stereopsis)
- Normal development requires both a match in strength of input from each eye AND a
coordination of
inputs
r alternation of two strong eyes, or amblyopia (one weak eye) USUALLY LEADS TO
poor stereopsis (depth vision)
Proper binocular visual development requires
- the proper convergence of the two eyes
- matching
* *refraction** and image quality
injection of 3h proline in one eye in adult reveals
ocular domiannce in v1
injection of 3h proline in one eye in the fetus reveals
no ocular dominance columns
strabismus in an adult can lead to
diplopia
Hebb’s hypothesis:
“Cells that fire together
wire together”
Experiments establishing, activity-based, Hebbian competition include:
- diff. between bincoular deprivation and monocular deprivation
- TTX silence retinal output supress MD
- GABA application silencing cortical cells supress MD
- Artificial electrical stimulation of the optic nerves after TTX injection in the eyes, synchronous or
asynchronous
what two experiments supressed moncular depirivation
injections fo TTX silencing retinal ouput (ganglion cells)
GABA in cotex blocking cortical cells
electrostim is applied synchronously to the two optic nerves, ___ OD columns form.
no segregated OD columns form.
electrostim is applied asynchronously to the two optic nerves, ___ OD columns form.
OD columns form
___ of NMDA receptors reduce ocular dominance plasticity and the refinement of
receptive-field properties
Antagonists
The overall concentration of NMDA receptors in the visual cortex peaks with the
critical period for
ocular dominance plasticity
The NMDA contribution to the visual response drops in layers ___ as ocular dominance
columns segregate.
4-6
Examples of adult cortical plasticity: (4)
- recovery from brain injury
- Rapid fill-in of the cortical representation after a retinal lesion, then axonal growth
- Analogous cortical reorganization of somatotopic maps under conditions of digit re-afferentation
- phantum limb
By depriving the sensory cortex of input what happened intially?
was silent in the region
deprived of input.
By depriving the sensory cortex of input what happened over time?
that cortical region
became active again, resulting in a shift in the
topographic maps
. The input
deprived cortex had “stolen” input from __ cortex,
using the same mechanisms of competition and plasticity
seen in the developing brain.
adjacent
activity in only one axon synapse may be insuffiecent to drive the post synaptic cell to threshold so it triggers ___ strengthening mechanism
hebbian
