week 5 - experience dependent plasticity

Question 1

watch this lecture again - went too fast

Question 2

Both LTD and LTP are NMDA dependent,
how can reverse effects share a mechanism?

Answer 2

figure this out

Question 3

Describe cortical maps

Answer 3

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

Question 4

describe ocular dominance stripes
(macaque, blasdel 1992)

Answer 4

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

Question 5

describe horton and hocking 1996

Answer 5

if you do the occular dominance experiment at birth you already see occular dominnance stripes

Question 6

describe crowley and katz 2000 horrible animal ocular dominance experiment

Answer 6

remove the eyeball of the animal at different stages.

read up on this

Question 7

describe retina inactivation in huberman et al 2003

Answer 7

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

Question 8

how does ocular dominance relate to hebbian plasticity?

Answer 8

activity-dependent plasticity prior to eye opening segregates inputs with uncorrelated spontaneaous activity

Question 9

how do you prove that hebbian plasticity is essential for this (iwasato et al 2000)

Answer 9

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

Question 10

what happens to the stripes post monocular deprivation? hubel and wisel 1977

Answer 10

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

Question 11

What do recordings of individual neurons show us about activity dependent plasticity in the eyes

Answer 11

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

Question 12

what do these studies show us?

Answer 12

*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

Question 13

explain orientation selectivity

Answer 13

review and explain

Question 14

what is the effect of NDMA blocking on orientation selectivity?

Answer 14

the development of orientation selectivity is blocked by NMDA antagonist APV (bear et al, 1990)

Question 15

what are orientation pinwheels?

Answer 15

there are some areas on the orientation selectivity map where the is areas of pinwheels where all orientations are next to each other

Question 16

how might you exeperimentally limit experience of orientation? (tanaka et al 2007)

Answer 16

put goggles on the head of a kitten where either horizontal or vertical features are represented

Question 17

how can you measure neural activity using calcium imaging?

Answer 17

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

Question 18

how can you prove orientation selectivity is experience dependent

Answer 18

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

Question 19

how does orientation selectivity change due to associative learning? as proof of experience dependent plasticity

Answer 19

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

Question 20

how does learning lead to improved stimulus representation in orientation selectivity

Answer 20

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

Question 21

what other evidence is there for orientation selectivity learning through sharpening of responses?

Answer 21

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