Describe sensory memory
- large capacity, but rapid decay
- sensory association areas involved
Describe short-term (working) memory
- lasts for seconds to minutes
- severely limited capacity
- available to conscious awareness
- prefrontal cortex involved
Describe intermediate-term memory
- lasts for hours and days
- may be transferred to LTM through rehearsal
What are the two types of long term memory?
Explicit (declarative) and implicit (non-declarative)
Describe declarative memory
- involves hippocampus and medial temporal lobes
- neurons in hippocampus register info about the space surrounding an animal
- cognitive map of the external environment
What is synpatic plasticity?
Change in synaptic function in response to patterns of use
What is synaptic facilitization/sensitization?
Repeated APs result in increased Ca n terminal, increased NT release
What is synaptic depression/habituation?
Repeated APs deplete NT in terminal, decreased NT release
What was Eric Kandel’s model of choice?
Aplusia californica (Sea Hare)
Why did Kandel pick aplysia?
- small number of neurons
- large neurons
- culturable neurons that form circuits in vitro
- responses are visible and measurable
- respone triggered by several electrical synapses firing simultaneously
What was the main reflex Kandel studied?
Gill withrawal reflex
Describe the difference between habituation and sensitization.
- Habituation
- repeated stimulus leads to “ignore”
- “negative” memory - not stored
- Sensitization
- stimulus results in response
- results in consolidated memory
What is the simplest formation of implicit learning?
Habituation
Describe habituation in terms of neurons (aplysia?)
- size of EPSP by sensory neuon on motor neuron decreases in amplitude
- inactivation of calcium channels
- less Ca2+entering nerve terminal of presynaptic membrane
- less NT released
Describe sensitization in terms of neurons.
- large increase in amplitude of EPSP
- increase in amount of NT released
- amplification due to interneurons
Describe signalling by the interneurons (short term sensitization)
- excitatory interneurons release serotonin (5-HT)
- 2 serotonin receptors in Aplysia
- 5-HT2 like receptor
- PLC pathway
- 5-HT4,6,7 like receptor
- adenylate cyclase pathway
- 5-HT2 like receptor
Storage of long-term memory results in ___________ in the presynaptic termini.
Physical changes.
- Habituation
- retraction of presynaptic termini
- in aplysia, 35 fewer connections with motor neurons and interneurons
- Sensitization
- increase in number of connections
- in aplysia, 2 fold increase
What were the long term changes in habituation and sensitization in the aplysia?
- normal aplysia showed 1300 axon terminals on sensory neurons
- aplysia experiencing sensitization had 2800 terminals
- aplysia experiencing habituation had 800 terminals
Describe long term sensitization.
- cAMP binds to and activates CREB
- cAMP response element binding protein
- MAPK may also be involved
- CREB translocates to nuclues and increases gene expression of specific gene
- changes protein profile of synapse - changes in size etc.
What is the feedback loop involved in long term sensitization?
- one gene synthesized in response to CREB is ubiquitin hydroxylase
- degreade regulatory domain of PKA
- results in continuous activity of PKA
- Ks is continuously phosphorylated
- AP prolonged
- Ca influx almost permanent
- continued release of NT
What is BDNF?
Brain-derived neutrophic factor
- activated by NMDA receptor
- in aplusia, blocking BDNF - no long term memory
- corticosteroids decrease BDNF
- activates growth of dendritic spines
- role in generation/localization of new receptors
What test tested the spatial memory of vertebrates?
Morris water maze
What NT/receptor are used in learning pathways for vertebrates?
Glutamate
Does the learning pathway in vertebrates require an influx of Ca2+ into the post-synaptic cleft?
Yes
