Plasticity of the Somatosensory system

Question 1

In people missing an arm, why when you touch their face they are able to feel as though their arm is being touched?

(2 marks)

Answer 1

• It’s a maladaptation
• MRI shows there’s no hand representation - but that if you stimulate the face region you find it has expanded into the hand representation
• Intracortical connections between the two areas

Question 2

What was found when two fingers were sown together?

(1 mark)

Answer 2

• Areas in cortex responded to more than one digit - unsual
• So - areas in cortex exist that will respond to cells with 2 digits

Question 3

Where does information from the whiskers project to? (cellular)

(2 marks)

Answer 3

• Information arrives from layer 4 and project vertically up and down the barrel columns
• And then laterally in pyrimidal cells

Question 4

If you cut all the whiskers on an animal and left one where would the strongest response be seen?

(2 marks)

Answer 4

• Strongest response in to D1 stimulation in D1 barrel
• Weaker ones in surrounding barrels

Question 5

What will be seen in terms of barrels if you allow the animal to walk around with just one whisker?

(1 mark)

Answer 5

Area for D1 whisker in cortex expands so will see D2 barrel respond just as well.

Question 6

Are the connections between barrel colums horizontal or vertical?

(1 mark)

Answer 6

Horizontal - and radiate out from individual barrel columns into neighbouring ones

Question 7

What was found when recordings were done in layer 2/3 whiskers?

(4 marks)

Answer 7

• Layer 2/3 cells respond very quickly
• Neighbouring barrel cells respond slower
• Due to a delay - information comes into neighbouring barrel and only relayed over by polysynaptic connections
• Proven by making lesion in barrel and lose slow latency responses from surrounding barrels

Question 8

How is information between the columns generated?

Answer 8

Intracortically

Question 9

How else can you prove the why there is a delay between the passing of information between barrels?

(3 marks)

Answer 9

• USe a GABA agonist (green lines) and you’ll lose responses in barrel
• Or block entire cortex with GABA and lose all responses
• But then locally activate GABA antagonist and record the response

Question 10

What happens if you get a lesion in the D1 barrel in an animal with SWE?

(2 marks)

Answer 10

• If it expands, it is due to the intracortical connections
• Therefore should lose all of expanded representation in barrels surrounding the D1 barrel column

Question 11

What happens when you destroy the D1 barrel in an animal with SWE?

(4 marks)

Answer 11

• Normally animal would be 2.5 x more sensitive to D1 whisker than normal
• But as you destroy D1 barrels response detirioates and start to lose response (everywhere?) around same time as D1 whisker destruction
• Shows plasticity is taking place entirely intracortically and the pathways between the barrels are important for transmitting potenitated representation of the spared whisker

Question 12

How do layer 4 cells project to allow thte travel of information?

(1 mark)

Answer 12

Diverge and project diagonally into neighbouring columns

Question 13

What is the protocol for making LTP and LDP in the different layers of the mouse?

(2 marks)

look up n go over answer??

Answer 13

• Stimulate with electrode in layer 4 and produce small current iont layer 2/3 - LTP
• Reverse this process so that the post synaptic potential happens before so get LDP

Question 14

Why does LTP occur?

(2 marks)

Answer 14

• NMDA R activation which causes Ca²⁺ to enterthe post ynaptic spine
• This induces AMPA R to eb inserted into the membrane and the more AMPAR the stronger teh synaptic transmission between pre and post synaptic terminals

Question 15

How does CamKII autophosphorylation take place?

(4 marks)

Answer 15

• NMDAR is actived by pre-synaptic glutamine which causes depolarisation of the membrane
• Ca²⁺ comes through and NMDAR and binds to calmodulin which binds to CamKII
• CamKII then phosphorylates AMPAR which leads to CamKII insertion into the membrane
• CamKII also phosphorylates itself (autophosphorylation) allwoing its activity to last a long time and so it can continue the process of synapse strengthening

Question 16

What is seen in the T286A mutant when LTP induction is attempted?

(2 marks)

Answer 16

• Map doesn’t show expansion like the one in WT
• No potentiation of intracortical pathways because no synaptic LTP and therefore no experience dependent on plasticity that occurs normally

Question 17

How is the number of cortical spines increased?

(3 marks)

Answer 17

• Whisker deprivation in form of chessboard pattern shown to increase filopedia turnover and simultaneously increase turnover of spines with stable morphology
• Changes in spine couopled with pre-synaptic terminal
• Depression occurs if only one is removed