WEEK 5 - The Cellular basis of learning and memory Flashcards
Learnign
the process of acquiring new information
what were the three conditions involved in the rat study regarding the effect of the environment on the brain
standard condition - normal cage
impoverished (or isolated) condition - less things in cage
enriched condition - more thingsi n cage
what was the findings of the rat study regarding the effect of the environment on the brain
rats in the enriched condition had heavier and thicker cortexes. larger cortical synapse and also increased growth in dendrites
what is environmental enrichment?
the brain grows and changes as a consequence of the environment. Evidence suggests long-term changes in brain structures occur as a result of experience
non-associative learning?
inolves a single stimulus presented once or repeated
associative learning
learning about connections or relationships between events
what are the two types of non-associative learning?
habituation and sensitization
what is habituation
decreased response to repeated presentations of a stimulus
sensitization
prior strong stimulation icnrease response to most stimuli
what is involved in non-assicative learning in aplysia californica
the sea-slug show a grill withdrawl response when water is squirted at its syphon. repeated stimulation decreases in the size of the response thus habituation. a small shock to tell the tail enhances the size of the response to subsequent water squirts thus sensation
what is the theory involved with associative learning?
classical and operant conditioning
classical conditioning
a neutral stimulus is paired with another stimulus that elicits a response. eventually the neutral stimulus by itself will elicit the response. associative leanring because association is learned between two previously unrelated stimuli
who was responsible for classical conditioning?
PAVLOV
operant and instrumental condition,
where an association is made between behaviour and the consequence of the behaviour. it is a form of associative learning where an action is learned between an action and its consequence
what did pavlov believe?
conditioning strengthened connections between the CS and the UCS center in the brain
what is the switchboard metaphor?
new connections are plugged between differeny areas
what did karl lashley do?
set out to test whether new connections are plugged in between differeny areas by searching for engrams, pr physical representations of what had been learnt in rat brain
what did karl lashley hypothesize?
that a knife cut should abolish newly learned response
what were the results of karl lashley’s experunent?
not consistent with switchboard metaphor. i.e location of cute did not matter. what did matter was the extent of lesioning and the complexity of the task
what did karl lashley propose in regards to his findings?
the mass action principle
what is the mass action principle?
suggests that the proportion of the brain that is injured is directly proportional to the decreased ability of memory functions. In other words, memory cannot be localized to a single cortical area, but is instead distributed throughout the cortex
what was involved in the stdy of how synaptic events underlie simple learning in invertebrates?
habituation and sensitization
what is habituations involvement in storing information in the neurons system of aplysia californica?
results in a change in the synapose between the sensory neurons and the motor neurons, sensory neurons fail to excite motor neurons as they did previously
what is sensitization involvement in storing information in the neurons system of aplysia californica?
changes as identified in synapse included:
serotonin release from a facilitating neuron blocks potassium channels in presynaptic neuron.
prolonged release of transmitter from that neuron results in prolonged sensitization
what did donald hebb say?
“cells that fire together wire together”
what is hebbian synapse?
occurs when the successful stimulation of a cell by an axon leads to the enhanced ability to stimulate that cell in the future.
why does the enhancement in the hebbian synapse occur?
becuase of simultaneous activity in the presynaptic and postsynaptic neurons
what are hebbian synapses critical for?
many kinds of assicative leanring
what did Bliss & Lomo demonstrate?
long term potentiated in the rabbit hippocampus occues when one or more axons are bombarded with a dendrite with stimulation (tetanus stimulation) leaving the synapose “potentiated” for a period of time and the neuron is more responsive
what is LTP
long term potentiated
what are the properties of LTP that suggest it as a cellular basis of leanring and memory?
specificity, associatibity
specificity in regard to LTP?
only synapses of a cell that have been highly active become strengthened
associativity in regard to LTP
pairing a weak input with a strong input enhances later responses to a weak input
since LTP exhibits specificity and associativity, what seems plausible?
a plausible mechanism for instantiate Hebbian learning
Long-term potentiation
an activity dependent enhancement of synaptic efficacy
long-term depression
is a prolonged decrease in response at a synapose that occurs when axon have been active at a low frequency (oppositve of LTP)
what do the biochemical mechanisms of LTP depend on?
changes in glutamate synapses primarily in the postsynaptic neuron (Excitatory)
where do the changes the LTP depend on occur?
several types of receptor sites including the ionotropic receptors
what are the ionotropic receptors where the changes the LTP depend on occur?
α-Amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors.
AND
N-methyl-D-aspartate (NMDA) receptors.
what is the process of LTP mechanisms in regard to hippocampal neurons?
o Repeated glutamate excitation of AMPA receptors depolarizes the membrane
o The depolarization removes magnesium ions that had been blocking NMDA receptors (NMDA receptor is action is voltage-dependent)
o Glutamate is then able to excite the NMDA receptors, opening a channel for calcium ions to enter the neuron
what does specificity require?
BOTH glutaminergic binding at the receptor (receptor relase at the pre-synaptic cell) and depolarisation of the post synaptic cell (to remove Mg2+block)
what triggers further changes in the process of LTP?
entry of calcium through the NMDA channel
what happens when more AMPA receptors are built?
dendritic branching is increased
what do the responses in the LTP in Hippocampal neurons increase?
later respnsiveness of the dendrites to incoming glutamate
what as another cause of LTP?
presynaptic neuron
what changes occur as a result of post synaptic cell stimulation?
release of the retrograde messeger transmitter that travels back to the presynaptic cell
what changes occur as a result of the release and travelling of the retrograde messenger transmitter
o Decrease in action potential threshold
o Increase neurotransmitter release of
o Expansion of the axons.
o Transmitter release from additional sites.
physiological changes at synapse may do what?
store information
what can changes be in regard to information storage in the newvous system?
presynaptic or post synaptic or both
what can changes include when storing information in the nervous system?
increased neuotransmitter release, or effectiveness or receptors
how can synaptic changes be measured?
physiologicall and may be presynaptic post synaptic or both
What is the relation between LTP and memory function?
their temporal properties are consistent with eachother
what did the Morris water maze find?
genetically modified mice with no NMDA receptors in the CA1 field of the hippocampus are unable to learn how to solve the maze
what was the experiment that relates to behavioural induction of LTP?
the rats in the different conditions of environemtn
what is the RIBOT gradient/temporal gradient of retrogade amnesia?
more remote memories tend to be spread where as more recent memories are lost
what is the first important explanation for temporal gradients in amnesia?
older memories become more semantic like and less episodic with the passing f time because they get rehearsed more often. They become mroe like stories than memries (Cermak & O’Connor)
what is the second important explanation for temporal gradients in amnesia?
the hippocamps has a time-limited role and the more consolidated the memory the less dependent on the hippocampus it is (Squire)
what is the difference between dementia patients and amnesic AD patients?
dementia patients can remember recent but not old events, and amnesic AD patients is the opposite
Somantic
can remember recent vents but not older events
Alzheimer’s or amnesia
can remember remote events by not revent events
what is the standard model of declarative system consolidation?
- consoliation
2. retrieval at different stages of consolidation
what are the different stages of consolidation?
- ecoding
- retrieval of non-consolidated memory
- retrieval of a consolidated memory
what is the initial storage of memory trace
pattern of connections between hippocampal and cortical neurons
what evidences supports the idea that memories are transferred from the hippocampus?
a longer time-course for system consolidation than for synaptic plasticity supports this
what does the protein synthesis inhibition following learning show?
synaptic consolidation is complete within 1 hour
what is the effect of leisoning the rat;s hippocapus on?
a learned response dimities of diminishes over time since learning. this takes a number of days
what is MTL and the neocortex?
complementary learning systems
what is structured and fast plasticity good for?
the online encoding of events as they happen
what are the benefits of structured and fast plasticity for online encoding of events?
sparse encoding, autoassociative, content addressable and recurent feedback loops
what do recurrent feedback loops allow?
binding across time and the reconstruction of previously learned patterns
what does the neocortex learn during consolidation of memoies?
generalize concepts, princoples, facts etc slowly through interleaved representation of the same event many times in the content of small changes of synaptic efficacy
what does recurrent connectivity in the hippocampal formation instantiate?
auto-associative memory systems
