Lecture 21: Memory and learning 2 Flashcards
What is memory stored as?
strength of connections between neurons in a network
How is memory localised in the brain?
distributed, rather than depending on single neurons
Where is a particular memory located?
usually located close to the region that responds to a specific modality
How does strengthening of synapses occur?
probably occurs via long term potentiation (LTP)
How does weakening of synapses occur?
via long term depression (LTD)
What is required for long term effect of strengthened synapses?
protein synthesis
Can individual neurons participate in several memories?
yes
When do synapses strengthen?
when the presynaptic terminals and post-synaptic neurons are active at the same time
When do synapses weaken?
when pre- and postsynaptic activity is not simultaneous
In which neurons does long term potentiation occur?
neurons which are active during a tetanus / conditioning stimulus
What is the post-synaptic mechanism of LTP?
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
What is CAMKII associated with?
postsynaptic density
What is CAMKII composed of?
rings of 10 subunits
What is the role of Ca2+-calmodulin?
disinhibits kinase activity
What is the role of CaMKII?
memory stored in a number of these molecules within rings that are phosphorylated
How is CAMKII activated?
autophosphorylates and phosphorylated CAMKII is active until dephosphorylated
What is another source of Ca2+ for plasticity other than NMDA receptors?
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
What is a major difference between sources of Ca2+ for plasticity?
timing of Ca2+ entry
What can back-propagating dendritic action potentials activate?
voltage-dependent Ca2+ channels
What does close association of back propagating action potentials and EPSPs lead to?
either LTP or LTD
depends on timing
What happens if an action potential precedes EPSP?
What happens if an action potential follows EPSP?
there will be LTD
there will be LTP
recording from two neurons at the same time
What happens when post-synaptic AP precedes EPSP?
total increase in Ca2+ is small which activates Ca2+-dependent phosphatase leading to LTD
What happens when NMDA-receptor mediated EPSP precedes post-synaptic AP?
increase in Ca2+ is much larger which activates CAMKII and leads to LTP
