week 5 - experience dependent plasticity Flashcards
watch this lecture again - went too fast
Both LTD and LTP are NMDA dependent,
how can reverse effects share a mechanism?
figure this out
Describe cortical maps
topographic representation of some features of the outside world onto the cortical space of the brain
e.g mice have whisker maps where each whisker is topographically mapped on the cortex
we have the same with our visual field, in the striate cortex
tootell et al, 1982, showed if you show a pattern on the visiual field, activitation of the cortex will show this pattern
describe ocular dominance stripes
(macaque, blasdel 1992)
If you only show an image to someone in one eye (blocked the other eye) stripes of activation form in the cortex. If you get them to close the other eye different stripes of activation forms
the brain keeps the two inputs seperate in the cortex until they reach the layer 2/3 of the cortex ? check this
describe horton and hocking 1996
if you do the occular dominance experiment at birth you already see occular dominnance stripes
describe crowley and katz 2000 horrible animal ocular dominance experiment
remove the eyeball of the animal at different stages.
read up on this
describe retina inactivation in huberman et al 2003
ferret experiment
if you use a toxin from frog to prevent retina activation, before the eyes open, this blurs the boundary of ocular dominance stripes
this shows you need activity for left and right eye stripes to be well formed
how does ocular dominance relate to hebbian plasticity?
activity-dependent plasticity prior to eye opening segregates inputs with uncorrelated spontaneaous activity
how do you prove that hebbian plasticity is essential for this (iwasato et al 2000)
if you do the same experiment above but remove NMDA receptor the effect is blocked
Shows it is hebbian platicity becasue plasticity is NMDA dependent
what happens to the stripes post monocular deprivation? hubel and wisel 1977
post monuclar deprivation, the non-deprived eye takes over and the stripes get bigger for that eye
This is an example of experience dependent plasticity
What do recordings of individual neurons show us about activity dependent plasticity in the eyes
pre-deprivation most neurons take input from both eyes
post-monocular deprivation, neurons have a bias to the open eye
if you do this experiment with a NMDA receptor block, you prevent this shift
what do these studies show us?
*Relatively crude maps, such as retinotopic maps are
largely not determined by neural activity instead requiring
concentration gradients and molecular addresses
* More detailed maps such as those including ocular
dominance and orientation selectivity require activity
and experience
* Ocular dominance and binocular integration are severely
affected by monocular deprivation or strabismus but
largely unaffected by binocular deprivation
* Ocular dominance plasticity is a competitive process
explain orientation selectivity
review and explain
what is the effect of NDMA blocking on orientation selectivity?
the development of orientation selectivity is blocked by NMDA antagonist APV (bear et al, 1990)
what are orientation pinwheels?
there are some areas on the orientation selectivity map where the is areas of pinwheels where all orientations are next to each other
how might you exeperimentally limit experience of orientation? (tanaka et al 2007)
put goggles on the head of a kitten where either horizontal or vertical features are represented
how can you measure neural activity using calcium imaging?
take gfp (green flourescent protein) and snip it
combine it with calmodulin
everytime calcium binds to calmodulin it closes the gfp and it becomes flouresenct
this is great because calcium is a good proxy for neural activity
how can you prove orientation selectivity is experience dependent
if you put the goggles on the kittens early in life
then you look at the orientation maps (using calcium flouresence imaging),
kittens with goggles early in life show inhibition of orientation selectivity because of the googles
this is not the case using kittens late in life
this suggests orientation selectivity is experience dependent but there is a critical period for this
how does orientation selectivity change due to associative learning? as proof of experience dependent plasticity
you can train yourself to spot things in your visual fields
e.g a radiologist can spot a fracture in an x-ray when a normal person can’t
you can study this with fMRI, or using patch clamps or electrode recording in mice or monkeys
how does learning lead to improved stimulus representation in orientation selectivity
learning leads to improved stimulus representations:
- stimulus amplitude increases
- number of neurons reacting to stimulus increases
- neurons develop less misfiring to non-specific orientations. The ‘sharpness’ of the firing in relation to the specific orientation increases
change in sharpness with learning is outlined by schoups et al 2001
what other evidence is there for orientation selectivity learning through sharpening of responses?
mice go through virtual reality corridor
looking at how the neurons light up through calcium imaging
reward task - if you see veritical they learn to lick the stripes, if not they learn not to lick
post learning, the orientation selectivity response of the neurons had sharpened
poort et al 2002
