Memory in Simple Organisms Flashcards
What is declarative memory?
Memory of facts
What is non-declarative memory?
Skills that we learn
What is a synaptotagmin?
A calcium sensor
All have different calcium sensitivities
Three pools of vesicles
Reserve or resting pool
Proximal pool
Readily releasable pool
AMPA receptor
Binds glutamate
Opens and massive Na+ influx
Leads to depolarisation
What does Phospholipase C do?
Increases Ca2+ concentration in the cytoplasm
NMDA receptor
Binds glutamate
When membrane depolarised, Mg2+ leaves receptor and receptor opens
Leads to calcium influx into the membrane
Advantages of simple systems
Usually large neuron size
Circuit complexity much simpler (easier to study)
Not as temperature-dependent as human neurons
Allow for mapping of neurons
What is habituation
A decrease in responsivity of a sensory system when it is stimulated many times
Sensitisation
When the nervous system responds to a particular stimulus more and more
Examples of habituation in humans
Eye blink reflex
Repetitive non-harmful stimulus presentation (living on a noisy road)
Visual attention
Emotional response (flying, exam stress)
Aplysia refelx
Withdrawal of the gill when siphon is touched (to protect the gill which is necessary for survival)
If you touch the siphon many times what happens?
The gill is withdrawn less, the reflex disappears
Habituation results from…
A reduced synaptic strength
When the synapse is stimulated many times, _____ vesicles are available for release, resulting in _____
Less
A smaller response
What happens in sensitisation?
L29, activated with electric shock, releases serotonin
Serotonin activates serotonin GPCRs which activate adenyl-cyclase
Adenyl-cyclase turns ATP into cyclic AMP and activates protein kinase A
PKA phosphorylates and inactivates K+ channels
This depolarises the membrane
Cell remains depolarised for longer, broader action potential, more vesicles released
Mechanism of Associative Learning
When neurons stimulated with conditioned stimulus, depolarisation occurs
This leads to Ca2+ influx which causes serotonin release
Ca2+ additionally activates adenyl-cyclase and causes more cAMP
Activates PKA which depolarises the membrane (through inactivation of K+ channels)
Needs simultaneous CS and UCS
Kemenes (2006) - key message
In addition to synaptic plasticity, there are other mechanisms which do not involve synapses directly
Kemenes (2006) - what was done?
Used Lymnaea
Single trial associative learning
Presented attractive stimulus (US; sucrose) and neutral stimulus (CS; amyl acetate)
Sucrose triggers feeding behaviour, amyl acetate doesn’t
After one trial, snail shows feeding behaviour to amyl acetate alone
Kemenes (2006) results
24 hours after single trial, long lasting depolarisation of CGC (cerebral giant cell)
This was the only change identified
Depolarisation lasted for weeks (14 days)
Depolarisation occurs after behavioural change occurs
Cerebral giant cell
Permits feeding behaviour
If it fires, feeding behaviour is permitted
If not, then it is not
Conclusion of Kemenes (2006)
Depolarisation of CGC neurone may be involved in long term memory
Depolarisation occurs after behaviour is observed, so not involved in short term memory
Long-term memory at least partially encoded at a site distant to the neurons producing a behaviour
