1. Concepts and Significance

Question 1

what are the 3 different types of activity-dependent synaptic plasticity? Which of these is NOT synapse-specific? Which is reversible?

Answer 1

1. short term plasticity -> reversible
2. long term plasticity: LTP/LTD
3. homeostatic plasticity -> not synapse specific

Question 2

What is Hebbian plasticity?

Answer 2

the concept ‘fire together, wire together’: refers to the need for both pre- and post-synaptic activity to occur simultaneously for long-term synaptic modification (LTP/LTD) to occur.

Question 3

What is ‘associative’ and ‘synapse-specific’ in the context of LTP? Describe classical experiments to demonstrate synapse specificity and associativity of LTP

Answer 3

experiment: with hippocampal slice preparation and stimulation with electrodes of the schaffer-collateral pathway -> LTP can be observed to follow Hebbian learning rules:
1. specificity: only activated synapses are potentiated
2. associativity: both strong and weakly activated synapeses undergo LTP

Question 4

What does the NMDA-R detect as a co-incidence detector in LTP? How do the molecular properties of NMDA-R enable this?

Answer 4

NMDA-R is usually blocked by Mg -> inhibits all passage.
High-freq. stimulation -> coincident activity in pre- and post-synapse -> NMDA-R is bound to glutamate by pre- activation AND senses depolarization of of post- -> Mg is removed causing a Ca2+ influx through NMDA -> AMPA-R restribution -> LTP/LTD

Question 5

What evidence supports the idea that LTP represents the synapse level mechanism of memory?

Answer 5

loss-of-function evidence: hippocampal lesion mice cannot form spatial memory & altered hippocampal LTP (no NMDA-R in CA1 region) also impairs spatial memory. -> Evidence that hippocampal LTP is necessary for memory.

detectability: if learning involves LTP, changes in synaptic efficacy should be detectable following learning -> field-potentials are increased on some electrodes of multi-electrode array in CA1 area & AMPA receptor trafficking is detected with GFP.

gain-of-function evidence: artificial creation of LTP in certain synaptic patterns, should create a ‘false memory’ for an event that did not happen: reactivating DG contextual fear conditioning neurons with blue light -> freezing behavior in mice as memory recall sign, even though the memory was not replayed.

Question 6

explain the high functional diversity of central synapses:

Answer 6

neurotransmitter receptors differ in properties: excitatory/inhibitory, slow/fast, strong/weak and neurotransmitters themself differ in strong/weak and response to repeated activity: facilitation/depression.

Question 7

what is neuroplasticity?

Answer 7

the brains ability to reorganize itself by adding/removing connections -> on smaller scale: synaptic plasticity, the ability of neuronal connections to change their efficacy of transmission in response to previous activity & on larger scale: influences behavior by info transfer and computational outcome.

Question 8

what are different forms of learning:

Answer 8

1. non-associative learning: habituation & sensitization
2. associative learning: classical/pavlovian conditioning