Transcript Learning and Memory

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

Retrieval
Incoming
information
Working
memory
Sight
Sound
Smell
Touch
Performance

Sensory Encoding
buffers
Short-term
storage
Long-term
storage

Consolidation
Loss of information
Multiple Trace Hypothesis of Memory
Strength of memory trace
10
High
Sensory buffer
Short-term memory
Intermediate-term memory
Long-term memory
9
8
7
6
5
4
3
2
1
Low
0
Input
Time
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
High
• 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.
Strength of memory trace
10
9
Sensory buffer
8
7
6
5
4
3
Low
2
1
0
Time
Input
Short-term memory
(Working memory)
• 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.
High
Strength of memory trace
• Lasts for seconds to minutes.
Sensory buffer
Short-term memory
Low
Input
Time
Intermediate-term Memory
• May be transferred to LTM through
rehearsal.
• Example: remembering where you
parked your car.
High
Strength of memory trace
• Lasts for hours and days.
Sensory buffer
Short-term memory
Intermediate-term memory
Low
Time
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
• memory fades away with time.
• unless there is rehearsal.
Rehearsal
Amount of information
100%
Day 1 Day 2
Day 7
• Example: reviewing notes after class.
Day 30
Interference Theory of Forgetting
• Better recall when presentation of information is spaced.
100
Percent Correct
Massed Learning
80
Spaced Learning
Massed
60
40
20
0
• Example: studying versus cramming.
Spaced
Interference Theory of Forgetting
• Better recall for items presented first (primacy) and last (recency) in
a list.
BOOK
CAP
HAWK
BALL
LETTER
BIRD
CAN
SHIRT
LION
DOOR
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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
BOOK
CAP
HAWK
BALL
LETTER
BIRD
CAN
SHIRT
LION
DOOR
Hypothesized Memory Processes
Performance
Retrieval
Incoming
information
Working
memory
Sight
Sound
Smell
Touch
Sensory
buffers
Encoding
Attention
Short-term
storage
Long-term
storage
Consolidation
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.
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
• Episodic
• Semantic
Non-declarative
• Procedural
• Perceptual
• Conditioning
• Non-associative
High
Strength of memory trace
Declarative
Low
10
Sensory buffer
Short-term memory
Intermediate-term memory
Long-term memory
9
8
7
6
5
4
3
2
1
0
Time
• Lasts for months and years.
• Takes a long time to consolidate.
Input
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
• association between stimulus-stimulus.
• hippocampus is involved.
• 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).
How general is this effect?
Mechanism for Classical Conditioning:
Hebbian learning
If a synaptic connection is repeatedly active at the same time a postsynaptic 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.
Perceptual Memory:
Priming
• 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.
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
Series of connected movements that become automatic with practice.
Other examples: how to tie a shoe lace, ride a bike, drive a manual
transmission, play piano.
Emotional Memory:
Conditioned Fear
• Association between stimulus-valence (pleasant-unpleasant).
• Amygdala is involved.
• Little Albert
• Conditioned to fear rats – hammer hitting metal.
• Extended to other furry animals and objects.
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
Memory can be subdivided into multiple categories
• involve distinct brain regions.
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
Long-term potentiation
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.
Synaptic plasticity
• LTP strengthens existing synapses and creates new ones.
• Important for recovery of function post stroke.
Presynaptic density
Before LTP
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 organism
A) 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 is
A) 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 hypothesis
B) law of effect
C) all-or-none principle
D) Hebb rule
E) law of summation
4) The ability to recall a series of events is referred to as
A) 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 in
A) 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.