Lecture 21: Memory and learning 2

Question 1

What is memory stored as?

Answer 1

strength of connections between neurons in a network

Question 2

How is memory localised in the brain?

Answer 2

distributed, rather than depending on single neurons

Question 3

Where is a particular memory located?

Answer 3

usually located close to the region that responds to a specific modality

Question 4

How does strengthening of synapses occur?

Answer 4

probably occurs via long term potentiation (LTP)

Question 5

How does weakening of synapses occur?

Answer 5

via long term depression (LTD)

Question 6

What is required for long term effect of strengthened synapses?

Answer 6

protein synthesis

Question 7

Can individual neurons participate in several memories?

Answer 7

yes

Question 8

When do synapses strengthen?

Answer 8

when the presynaptic terminals and post-synaptic neurons are active at the same time

Question 9

When do synapses weaken?

Answer 9

when pre- and postsynaptic activity is not simultaneous

Question 10

In which neurons does long term potentiation occur?

Answer 10

neurons which are active during a tetanus / conditioning stimulus

Question 11

What is the post-synaptic mechanism of LTP?

Answer 11

glutamate excites AMPA-Rs and unblocks NMDA-Rs for next EPSP -> Ca2+ entering via NMDA-Rs activates Ca2+ dependent kinases which phosphorylate AMPA-Rs and cause insertion of AMPA-Rs into postsynaptic membrane -> Ca2+ can also enter via voltage-gated Ca2+-channels

Question 12

What is CAMKII associated with?

Answer 12

postsynaptic density

Question 13

What is CAMKII composed of?

Answer 13

rings of 10 subunits

Question 14

What is the role of Ca2+-calmodulin?

Answer 14

disinhibits kinase activity

Question 15

What is the role of CaMKII?

Answer 15

memory stored in a number of these molecules within rings that are phosphorylated

Question 16

How is CAMKII activated?

Answer 16

autophosphorylates and phosphorylated CAMKII is active until dephosphorylated

Question 17

What is another source of Ca2+ for plasticity other than NMDA receptors?

Answer 17

dendritic action potentials open voltage-dependent Ca2+ channels in dendritic spines
Ca2+ also released from intracellular stores e.g. metabotropic glutamate receptor causes Ca2+ release from ER

Question 18

What is a major difference between sources of Ca2+ for plasticity?

Answer 18

timing of Ca2+ entry

Question 19

What can back-propagating dendritic action potentials activate?

Answer 19

voltage-dependent Ca2+ channels

Question 20

What does close association of back propagating action potentials and EPSPs lead to?

Answer 20

either LTP or LTD

depends on timing

Question 21

What happens if an action potential precedes EPSP?

What happens if an action potential follows EPSP?

Answer 21

there will be LTD
there will be LTP
recording from two neurons at the same time

Question 22

What happens when post-synaptic AP precedes EPSP?

Answer 22

total increase in Ca2+ is small which activates Ca2+-dependent phosphatase leading to LTD

Question 23

What happens when NMDA-receptor mediated EPSP precedes post-synaptic AP?

Answer 23

increase in Ca2+ is much larger which activates CAMKII and leads to LTP