Synaptic Plasticity And Memory Flashcards
What is the critical period?
-the time period in development when the genetically determined patterns of brain circuitry are particularly subject to environmental refinement
What happens to the deprived eye in monocular deprivation?
It loses target space. There is competition with the other eye.
What can you say about the consequences of alternation deprivation?
There will be no binocular cells and therefore no stereopsis
What is the critical period length?
2-4 years
What are the 2 important mechanisms at work in the formation of ocular dominance columns?
- competition for target space between fibers from the 2 eyes
- coopération between fibers from the same eye
What does Hebb’s postulate for learning say?
Coincident activity in pre and postsynaptic elements of a synapse leads to its strengthening (increased efficacy)
What mediates the strengthening of synapses in developing V1?
NMDA-receptor dependent mechanism
What can you say about the NMDA receptor?
It is both a ligand and voltage gated ion channel.
Ligand: glutamate
Voltage gate: Mg++ block of channel af a resting Vm
Once opened, the NMDA channel allows for Ca2+ and Na+ to enter
What does the increase in intracellular Ca++ activate?
2nd messenger systems leading to strengthening of active synapses
Why is NMDA receptor said to be a coincidence detector?
- Channel opened only when both pre and post synaptic elements are synchronously active (Hebbian learning)
- Presynaptic cell is active - it’s releasing glutamate
- Postsynaptic cell is active - it’s depolarized and therefore Mg++ block in NMDA receptor is removed
- Na+ and Ca++ enter the postsynaptic cell
- Increased intracellular Ca++ initiates a cascade of events leading to increased synaptic strength
Explain the formation of the corals pattern of connections between weeks 2-13
- Initially there is a coarse map As both eyes try to generate a retinotopic map in the single layer 4C
- Activity dependent processes of cooperation and competition follow Hebb’s rule: sharpens terminal segregation
- End up with a precise retinotopic map and also segregation of L and R eye influences in layer 4C
Where is declarative memory formed?
Medial temporal lobe
Where is non declarative memory (procedural memory) formed?
Cerebellum, basal ganglia
What’s difference between retrograde and anterograde amnesia?
Retro: memory loss for events before the trauma
Antero: inability to form new memories following trauma
What does the hippocampus do?
It is involved in learning and memory, including spatial learning and memory
What is perseveration?
Repetition of choices even when they are incorrect
Wh are the microcircuits of the hippocampus?
- Perforant path: enthorinal cortex—>dentate gyrus
- Mossy fiber pathway: dentate gyrus —>CA3
- Schaffer collateral: CA3–>CA1 (place cells)
What do the Place cells of the CA1 pyramidal neurons serve as?
Output of the hippocampus
What influences the position of place field (place cells)?
External cues: landmarks in chamber
Internal cues: visual cues
Vestibular cues due to self motion
What does navigation require?
A map of space and a compass to tell direction
What are the cells responsible for the “compass”? Where are they located?
Head direction specific cells in the postsubiciculum
What do rats use to code for head direction?
They use internal and external cues
What are the three cells involved in spatial memory? Where are they each located?
- place cells: hippocampus (CA1)
- head direction cells (subiculum)
- grid cells (medial enthorinal cortex)
What is LTP?
Long Term Potentiation
What is required for LTP
Synapses must be active at the same time that the postsynaptic CA1 neuron is strongly depolarized
How do you achieve necessary depolarization with a tetanus?
- High frequency stimulation causes temporal summation
2. Enough synapses must be active to achieve spatial summation
What is the postsynaptic cell depolarized by? (What causes the Mg2+ to remove itself?)
AMPA receptor
What are the mechanisms of LTP in CA1?
1) Ca2+ entering through NMDA receptor activates calcium dependent protein kinases
2) kinases change effectiveness of existing postsynaptic AMPA receptors by phosphorylating them
3) kinases stimulates insertion of new AMPA receptors into the membrane
How do you induce LTD?
Synapses must be active at the same time that the postsynaptic CA1 neuron is weakly depolarized
What are protein kinases and protein phosphatases each activated by? What do they each yield?
Kinases: high Ca2+ and yields LTP
Phosphatases: low Ca2+ and yields LTD
