learning and memory. lecture outline hypotheses of learning and memory short-term memory long-term...
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Learning and Memory
Lecture Outline
• Hypotheses of learning and memory
• Short-term memory
• Long-term memory
• Learning and synaptic plasticity
Lecture Outline
• Hypotheses of learning and memory
• Multiple memory processes
• Multiple memory traces
• Multiple memory systems
• Short-term memory
• Long-term memory
• Learning and synaptic plasticity
Why are learning and memory important?
• To be able to adapt to changes in the environment
• Learning• Acquire and process information from the
environment.
• Changes the nervous system
• Memory• Ability to retain this information.
Hypothesized Memory Processes
Incoming informati
on
Performance
Retrieval
Working memory
Short-term storageEncodin
g
Long-term
storage
Consolidation
Sensory
buffers
Sight
Sound
Smell
TouchLoss of information
Multiple Trace Hypothesis of Memory
Se-ries1
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Sensory bufferShort-term memoryIntermediate-term memory
Time
Str
en
gth
of
mem
ory
tra
ceHigh
Low
Input
Multiple Memory Systems Hypothesis
• Memory can be divided into categories that reflect the type of information being remembered.
• Each system primarily employs a distinct brain region.• Declarative Hippocampus • Procedural Basal Ganglia• Emotional Amygdala • ‘Working With’ Memory Prefrontal Cortex
Sensory memory
• Large capacity, but rapid decay.
• Sensory association areas involved.
• Example: Your mother is lecturing you and you aren’t paying attention, however, if asked, you can repeat the last sentence she said.
High
Low
Input
Short-term memory(Working memory)
• Lasts for seconds to minutes.
• Severely limited capacity.
• magical 7 ± 2 – digits, letters, etc.
• Available to conscious awareness.
• Prefrontal cortex involved.
• Example: remember a phone number. between looking it up and dialing.
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Time
Stre
ngth
of m
emor
y tra
ce
Sensory buffer
Short-term memory
High
Low
Input
Intermediate-term Memory
• Lasts for hours and days.
• May be transferred to LTM through rehearsal.
• Example: remembering where you parked your car.
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Time
Str
engt
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mem
ory
trac
e
Sensory buffer
Short-term memory
Intermediate-term memory
High
Low
Input
STM and Forgetting
Decay theory• memory fades away with time, unless there
is rehearsal.
Interference theory• memory for other material interferes with
information we are trying to remember.
Decay Theory of Forgetting
100%Rehears
al
Day 1 Day 2 Day 7 Day 30
• Example: reviewing notes after class.
Am
ount
of
info
rmati
on
• memory fades away with time.• unless there is rehearsal.
Interference Theory of Forgetting
• Example: studying versus cramming.
0
20
40
60
80
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Per
cent
Cor
rect
Massed Learning
Spaced Learning
• Better recall when presentation of information is spaced.
Massed
Spaced
Interference Theory of Forgetting
BOOK CAP HAWK BALL LETTER BIRD CAN SHIRT LION DOOR
• Better recall for items presented first (primacy) and last (recency) in a list.
Mechanisms of Primacy and Recency
Primacy: • Memory system has enough resources
to transfer items at the beginning of a list into LTM.
Recency: • Items at the end of the list are still in
STM and are therefore available for recall.
1. BOOK 2. CAP 3. HAWK 4. BALL 5. LETTER 6. BIRD 7. CAN 8. SHIRT 9. LION10. DOOR
Hypothesized Memory Processes
Incoming informati
on
Performance
Retrieval
Working memory
Short-term storageEncodin
g
Long-term
storage
Consolidation
Sensory
buffers
Sight
Sound
Smell
TouchAttention
Rehearsal
Factors Affecting Primacy and Recency
• A distractor task at the end of a list interfered with recency, but not primacy.• Interrupts rehearsal.
• A faster presentation rate interfered with primacy, but not recency.• Increases load and effects transfer of information
from STM to LTM.
• Changing the length of delay between training and testing interfered with both primacy and recency.
Effect of Delay on Primacy and Recency
Series140
60
80
100Test immediately
Test after short delay
Test after long delay
Serial Position of Memory Item
Perc
en
t C
orr
ect
PrimacyRecency
Consolidation
• Hippocampus and amygdala involved.
• Memories are subject to modification during reactivation and reconsolidation.
• Memories are more likely to reflect how person perceived the event, rather than what actually happened. • Confidence is not correlated with accuracy.• Implications for eyewitness accounts, repressed
memories of abuse.
Story so far…
Learning and memory involves multiple processes, traces and systems.
• Processes• Encoding, consolidation and retrieval.
• Traces• Sensory, short-, intermediate- and long-term.
• Systems• Declarative, procedural, emotional, ‘working-
with’.
Long-term memory
• Lasts for months and years.• Takes a long time to consolidate.
High
Low
Input
Declarative• Episodic• Semantic
Non-declarative• Procedural• Perceptual• Conditioning• Non-associative
Declarative memory
• Knowledge we have conscious access to. • Often referred to as explicit memory.
• Episodic• Personal experiences / events etc.
• Canoeing on Lake Winnipeg, surfing in San Diego.
• Often referred to as autobiographical memory.
• Semantic• Conceptual knowledge
• “Where is Lake Winnipeg, where is San Diego?”
• “How do you canoe, how do you surf?”
Classical Conditioning
• Unconditioned stimulus (US)• stimulus (puff of air) that
produces UR.
• Unconditional response (UR) • reflex (eye blink) to US.
• Conditional stimulus (CS) • an arbitrary stimulus (tone)
paired closely in time with an US.
• Conditioned response (CR) • behaviour (blinking) now occurs
in response to CS (without need for US).
• association between stimulus-stimulus.• hippocampus is involved.
How general is this effect?
Mechanism for Classical Conditioning: Hebbian learning
If a synaptic connection is repeatedly active at the same time a post-synaptic neuron fires, then this will lead to changes in the structure or chemistry that strengthen the connection.
Non-declarative Memory
• Performance informed by implicit knowledge.
• Perceptual memory• Priming
• Procedural memory• Operant / instrumental conditioning
• Emotional memory• Conditioned fear response
• Non-associative memory • Habituation / sensitization
Perceptual Memory: Priming
• An alteration of response to a stimulus as a result of prior exposure.
• Can last for hours.• Not dependent on level of processing.• Reduced (but not eliminated) when presentation and
test modalities are different.• Perceptual short-term memory involves the sensory
association cortices.
Perceptual Memory: Priming
Procedural Memory: Instrumental / Operant Conditioning
Pressing a button provides a reward. • Increases the likelihood that the animal will press
the button again.
Procedural Memory: Instrumental / Operant Conditioning
• Association between stimulus-response.• Stimuli following a behaviour can be either:
• Reinforcing: perceived as positive.• Punishing: perceived as negative.
• Basal ganglia are involved.
Procedural Memory: Motor Learning
Other examples: how to tie a shoe lace, ride a bike, drive a manual transmission, play piano.
Series of connected movements that become automatic with practice.
Emotional Memory: Conditioned Fear
• Little Albert• Conditioned to fear rats – hammer hitting
metal.• Extended to other furry animals and
objects.
• Association between stimulus-valence (pleasant-unpleasant).
• Amygdala is involved.
Emotional Memory: Conditioned Fear
• Nothing lasts forever! • If CS is repeated without US often enough, then the
CR disappears (extinction).
Non-associative Memory: Habituation
• Ignore incoming information that is not relevant.• Most basic form of learning.
• Even worms can do it.• Tap response
C. elegans
Short-term memory• Prefrontal cortex,
sensory association areas
Declarative long-term memory
• Hippocampus
Procedural long-term memory
• Basal ganglia, motor association areas, cerebellum
Emotional long-term memory
• Amygdala
Memory can be subdivided into multiple categories• involve distinct brain regions.
A long-term increase in the excitability of a neuron to a particular synaptic input caused by repeated high-frequency activity of that input.
• EPSP’s are summated as successive EPSP’s occur and before past EPSP’s have dissipated.
Long-term potentiation
Synaptic plasticity
• LTP strengthens existing synapses and creates new ones.
• Important for recovery of function post stroke.
Before LTP
Presynaptic density
After LTP
Synaptic structure
Before LTP After LTP
Take Home Message• Memory is multifaceted.
• Many processes, traces, systems and brain regions involved.
Review Questions
1) In classical conditioning, an organismA) learns the consequences of a specific behavior.B) identifies and categorizes objects.C) shows a species-typical behavior in response to a previously unimportant stimulus.D) is able to recognize objects by the sounds they make.E) forms an association between a response and a stimulus.
2) You are listening to a song on the radio while doing your homework. The phone rings. Your mother has called to tell you that your favorite uncle has died after being hit by a car. Three months later, you again hear the same song and suddenly feel very sad. In this example, the unconditional response isA) the voice of your mother as she relays the bad news.B) listening to the song.C) your feeling about the song prior to the phone call.D) your feeling about your uncle before he died.E) feeling sad when your mother calls with the bad news.
Review Questions
3) The ________ states that a weak synapse will be strengthened if its activation occurs at the same time that the postsynaptic neuron fires.A) perforant path hypothesisB) law of effectC) all-or-none principleD) Hebb ruleE) law of summation
4) The ability to recall a series of events is referred to asA) serial memory.B) spatial learning.C) perceptual learning.D) episodic learning.E) observational learning.
5) Intense electrical stimulation of axons within the hippocampal formation results inA) long-term potentiation of postsynaptic neurons.B) axoaxonic inhibition of presynaptic neurons.C) recurrent inhibition of the stimulated axons.D) long-term potentiation of presynaptic neurons.E) B and C are correct.