Synaptic Plasticity And Memory

Question 1

What is the critical period?

Answer 1

-the time period in development when the genetically determined patterns of brain circuitry are particularly subject to environmental refinement

Question 2

What happens to the deprived eye in monocular deprivation?

Answer 2

It loses target space. There is competition with the other eye.

Question 3

What can you say about the consequences of alternation deprivation?

Answer 3

There will be no binocular cells and therefore no stereopsis

Question 4

What is the critical period length?

Answer 4

2-4 years

Question 5

What are the 2 important mechanisms at work in the formation of ocular dominance columns?

Answer 5

• competition for target space between fibers from the 2 eyes
• coopération between fibers from the same eye

Question 6

What does Hebb’s postulate for learning say?

Answer 6

Coincident activity in pre and postsynaptic elements of a synapse leads to its strengthening (increased efficacy)

Question 7

What mediates the strengthening of synapses in developing V1?

Answer 7

NMDA-receptor dependent mechanism

Question 8

What can you say about the NMDA receptor?

Answer 8

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

Question 9

What does the increase in intracellular Ca++ activate?

Answer 9

2nd messenger systems leading to strengthening of active synapses

Question 10

Why is NMDA receptor said to be a coincidence detector?

Answer 10

• 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

Question 11

Explain the formation of the corals pattern of connections between weeks 2-13

Answer 11

• 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

Question 12

Where is declarative memory formed?

Answer 12

Medial temporal lobe

Question 13

Where is non declarative memory (procedural memory) formed?

Answer 13

Cerebellum, basal ganglia

Question 14

What’s difference between retrograde and anterograde amnesia?

Answer 14

Retro: memory loss for events before the trauma

Antero: inability to form new memories following trauma

Question 15

What does the hippocampus do?

Answer 15

It is involved in learning and memory, including spatial learning and memory

Question 16

What is perseveration?

Answer 16

Repetition of choices even when they are incorrect

Question 17

Wh are the microcircuits of the hippocampus?

Answer 17

1. Perforant path: enthorinal cortex—>dentate gyrus
2. Mossy fiber pathway: dentate gyrus —>CA3
3. Schaffer collateral: CA3–>CA1 (place cells)

Question 18

What do the Place cells of the CA1 pyramidal neurons serve as?

Answer 18

Output of the hippocampus

Question 19

What influences the position of place field (place cells)?

Answer 19

External cues: landmarks in chamber

Internal cues: visual cues
Vestibular cues due to self motion

Question 20

What does navigation require?

Answer 20

A map of space and a compass to tell direction

Question 21

What are the cells responsible for the “compass”? Where are they located?

Answer 21

Head direction specific cells in the postsubiciculum

Question 22

What do rats use to code for head direction?

Answer 22

They use internal and external cues

Question 23

What are the three cells involved in spatial memory? Where are they each located?

Answer 23

• place cells: hippocampus (CA1)
• head direction cells (subiculum)
• grid cells (medial enthorinal cortex)

Question 24

What is LTP?

Answer 24

Long Term Potentiation

Question 25

What is required for LTP

Answer 25

Synapses must be active at the same time that the postsynaptic CA1 neuron is strongly depolarized

Question 26

How do you achieve necessary depolarization with a tetanus?

Answer 26

1. High frequency stimulation causes temporal summation

2. Enough synapses must be active to achieve spatial summation

Question 27

What is the postsynaptic cell depolarized by? (What causes the Mg2+ to remove itself?)

Answer 27

AMPA receptor

Question 28

What are the mechanisms of LTP in CA1?

Answer 28

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

Question 29

How do you induce LTD?

Answer 29

Synapses must be active at the same time that the postsynaptic CA1 neuron is weakly depolarized

Question 30

What are protein kinases and protein phosphatases each activated by? What do they each yield?

Answer 30

Kinases: high Ca2+ and yields LTP
Phosphatases: low Ca2+ and yields LTD