Download PSY393 Cognitive Neuroscience Memory

Overview
PSY393 Cognitive Neuroscience
Memory
• Introduction
• H.M.
• Short-term memory
• Sensory memory
• Short-term memory store
Donna Rose Addis
13 Nov 2003
• Long-term memory
• The model of long term memory
• Neuroanatomy of long term memory
Introduction
H.M.: Who is he?
• The most famous case of amnesia
• What is learning and memory
• Learning = acquisition
• Memory = persistence of learning
• Stages of learning and memory
• Encoding – study phase
• Storage – retention interval
• Retrieval – test phase
• Case details:
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Absence seizures started at 10 yrs old
Generalized seizures started at 16
Medication were not controlling seizures
At 27 yrs: Surgery to remove his medial temporal
lobe bilaterally
H.M.: Areas of brain damage
• Removal of bilateral medial temporal lobe
H.M.: Areas of brain damage
• Removal of bilateral medial temporal lobe
Hippocampus (1)
Hippocampus (1)
Parahippocampal
gyrus (2)
Parahippocampal
gyrus (2)
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H.M.: Areas of brain damage
• Removal of bilateral medial temporal lobe
H.M.: Who is he?
• Result of this surgery: Global amnesia
• Anterograde amnesia:
- unable to form new long-term memories
• Retrograde amnesia:
- unable to retrieve any memories from the 11 yrs
before his surgery
- Because of his seizures?
• BUT other aspects of memory are preserved,
Hippocampus &
parahippocampal
gyrus removed
• e.g., short term memory
• Dissociation indicates separate memory systems
Short-term memory
MEMORY
Short-term memory
STM: Sensory Memory
• Very short duration (seconds)
Long-term memory
• Decays rapidly – tested by partial report
• Capacity: ~ 12 items
Sensory memory
Iconic memory
Echoic memory
Short-term / working
memory
Visuospatial sketchpad
• Echoic memory:
- Sensory memory for auditory information (echo)
Phonological Loop
Central Executive
• Iconic memory:
- Sensory memory for visual information (afterimage)
STM: STM store
• Short-term Memory
• Duration: seconds to minutes
STM: STM store
• Ways of testing short-term memory
- Visual memory: Rey Complex Figure COPY
• Capacity: Magic number 7 ± 2 chunks
• Ways of testing short-term memory
- Visual memory: geometric figures that are
difficult to verbalize
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STM: STM store
STM: STM store
• Ways of testing short-term memory
- Visual memory: Rey Complex Figure RECALL
• Ways of testing short-term memory
- Verbal memory: stories, word pairs, word lists
• Serial position effect:
- Primacy vs. Recency effects
Primacy
STM: Serial Position effect
Recency
STM: Modal model
• Primacy effect
• (Atkinson & Shiffrin, 1968)
- more rehearsal, enters LTM
- Faster presentation rate = Ð primacy
• Recency effect
- Info still in STM, so dumped out
- Distractor at end of list = Ð recency
Sensory Inputs
Sensory memory
ATTENTION
Primacy
Recency
Short-term storage
REHEARSAL
Long-term storage
STM: Levels of Processing
• (Craik and Lockhart, 1972)
• Effectiveness of different encoding strategies
• Deeper encoding more effective
- e.g., Is it living?
- Elaborative – relate info to previous knowledge
• Shallow encoding not as effective
- (e.g., font size)
- Processing only surface features
• Not consistent with modal model
• Getting info into LTM not just about how long you hold
it in STM, but how you process it
STM: Lesion evidence
• Patient H.M.: Spared STM, Impaired LTM
• Can repeat and remember 5 digits as long as he isn’t
distracted from rehearsing
• BUT this information doesn’t get into LTM
• Described as “marooned in the moment”
• Patient E.E.: Impaired STM, Spared LTM
• Tumour in inferior parietal/superior temporal cortex
• Impaired STM, preserved LTM
Double
Dissociation
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Long-term memory: Explicit Memory
• Episodic memory (Tulving, 1972)
MEMORY
Short-term memory
Long-term memory
Explicit memory
(Declarative memory)
Episodic
Semantic
(events)
(facts)
• Specific personal
experiences from
particular time & place
LTM: Explicit Memory
- Personally experienced events
- Specific time and place – context
- Conscious awareness that it is our personal past,
we remember that we did that, we can recollect
details about the context
- e.g., remembering when you first held your
baby sister
• General Knowledge
LTM: Explicit Memory
• Semantic memory
(Tulving, 1972)
- Facts we know about the world
- Lacks contextual information
- Even if we remember the episode we acquired the
fact, the fact itself is distinct
- e.g., knowing that Mr. Tim Hortons was a hockey
player for the Leafs
LTM: Explicit Memory
• Semantic Dementia
- Damage to the anterior inferior temporal cortex
- Impaired semantic memory: Impaired at naming
objects, can’t tell you about famous people or
events
- Spared episodic memory
• Consider these patients and K.C.:
Double
Dissociation
LTM: Explicit Memory
• Patient K.C. (Rosenbaum et al., 2000)
- Damage to his hippocampus bilaterally (motorbike
accident)
- Spared semantic memory, e.g., defining words
- Spared personal semantic memory, e.g., names of
work friends
- Impaired episodic
memory: e.g., cannot
recall any specific
episodes at work
or with those friends
LTM: Testing Explicit Memory
• Recall versus Recognition
- Recall: e.g., tell me what words were on the list
- If a patient can’t recall a memory, it could mean
either they just can’t retrieve it, or there is no
memory there to retrieve
- Recognition: e.g., was DEFINE on the list? Y/N
- We are providing direct cues to the information
- Even if their retrieval processes are not working
effectively, if the information is there, they will be
able to recognize it
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LTM: Testing Explicit Memory
LTM: Testing Explicit Memory
• The Remember-Know paradigm
• The Remember-Know paradigm: Patient Jon
- Can test whether someone has an episodic or
semantic memory of some information
- “I remember when ….” vs. “I know that ……”
- E.g., a famous name such as “Princess Diana” or
“Margaret Thatcher”
- Answer Remember if you can actually remember a
personal episode connected to her
- Answer Know if you know who this person is, but
can’t remember a specific episode
LTM: Testing Explicit Memory
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Hippocampal damage as a baby
Some personal events he could remember
Some he was only knew about
Greater activation of his residual hippocampus
when retrieving “remembered” events versus
“known” events
LTM: Testing Explicit Memory
• Verbal and Visual memory
- Verbal memory: word-pairs and stories after
a delay
- Visual memory: Rey complex figure after
delay
TRY IT!!
• Verbal & visual memory (encoding & retrieval)
- Verbal memory: supported by the left MTL
- Visual memory: supported by the right MTL
- e.g., temporal lobe epilepsy patients with damage
to :
- Left medial temporal lobe = difficulties mainly
with verbal memory
- Right medial temporal lobe = difficulties mainly
with visual memory
Double
Dissociation
LTM: Explicit Memory
LTM: Explicit Memory
• Anterograde memory
• Anterograde memory
- Memory for information since the brain injury
- Represents ability to form new LTMs
• Retrograde memory
• Retrograde memory
- Memory for information presented before the brain
injury
- Represents ability to retrieve older LTMs
- Temporally graded or flat gradient
Retrograde
Amnesia
INJURY
temporal gradient
- Memory for information since the brain injury
- Represents ability to form new LTMs
Anterograde
Amnesia
- Memory for information presented before the brain
injury
- Represents ability to retrieve older LTMs
- Temporally graded or flat gradient
Retrograde
Amnesia
time
flat gradient
INJURY
Anterograde
Amnesia
time
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LTM: Explicit Memory
Long-term memory: Implicit Memory
• Often get some degree of both, e.g., H.M.
• Why? Depend to some extent on the same
brain structures (e.g., hippocampus)
• Patient M.L.: Isolated retrograde amnesia
- Severe retrograde amnesia
- Initially had anterograde amnesia but this resolved
quickly
MEMORY
Short-term memory
Long-term memory
Explicit memory
Implicit memory
(declarative memory)
(non-declarative memory)
Procedural
Memory
Perceptual
Representation
System
Classical
Conditioning
Non-associative
learning
Dissociation
LTM: Implicit Memory
LTM: Implicit Memory
• Implicit memory typically outside of awareness
• Procedural memory
- Learning skills; e.g., riding a bike, mirror-drawing
2nd day
3rd day
Number of errors
1st day
• Perceptual priming
- Being primed to use certain information
- Shown a list of words such as DEFINE
- Later given stems and asked to complete it with
the first word that comes to mind:
- e.g., DEF Î Most likely to give DEFINE even if
you can’t explicitly remember that word being on
the list
Attempts each day
LTM: Implicit Memory
LTM: Implicit Memory
• Is implicit memory impaired in amnesia?
• Classical conditioning
- Pavlovian conditioning
- conditioned stimulus paired with an unconditioned
stimulus
• Non-associative learning
- e.g., habituation or sensitization
- Often when explicit memory is impaired, implicit
memory remains intact
• Patient H.M.: Mirror drawing
- Got faster each time, made less errors
- Indicates he was “learning” this task
- BUT each time, he had no explicit memory that he
had ever seen this task before
• Patient H.M.: Priming
- Completed word stems with words from the list
even though he had no explicit memory for them
being on the list
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LTM: Implicit Memory
• Are there patients showing the opposite?
• Patient M.S.: Priming
- Damage to the right occipital lobe
- Impaired on priming tasks, but spared explicit
memory
• Parkinson’s disease: Procedural memory
- Damage to the basal ganglia
- Impaired on skill learning; also habituation
LTM: Neuroanatomy
• What regions of the brain support LTM?
• What role do they play?
• What’s the evidence?
• Lesion cases
• Neuroimaging
Double
Dissociation
LTM: Role of the medial temporal lobes
• Medial temporal lobes
- H.M. was the first case to highlight the importance
of the MTL in forming new memories and
retrieving old memories
- Anterograde amnesia
- Retrograde amnesia (temporal gradient)
So, the MTL is important in LTM …
... But what does it do?
LTM: Role of the medial temporal lobes
• Medial temporal lobes and encoding:
- Forms links between information (Eichenbaum, 1991)
- e.g., between items (banana – dog)
- e.g., between an item and its context (the word
DEFINE was in list 2)
- Detects novel stimuli (Tulving et al., 1994)
- Activates more when encoding information we
haven’t seen before
- Continuously records experience (Moscovitch, 1992)
LTM: Role of the medial temporal lobes
• fMRI: MTL is active during successful encoding
Wagner et al., 1998
LTM: Role of the medial temporal lobes
• What is the role of the MTL in LTM?
1. Consolidation hypothesis (Squire)
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When just encoded, memories are dependent
on the hippocampus for retrieval
-
After a while, they become “consolidated”,
i.e., independent of the MTL, dependent on
the cortex
-
Explains temporal gradients: information not
yet consolidated cannot be retrieved once
hippocampus is damaged
Retrograde
Amnesia
INJURY
Anterograde
Amnesia
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LTM: Role of the medial temporal lobes
• What is the role of the MTL in LTM?
LTM: Role of the medial temporal lobes
• fMRI: Retrieving details of episodic memories
1. Consolidation hypothesis
2. Multiple Trace Theory (Nadel and Moscovitch, 1997)
-
Hippocampus important in retrieval of ALL
truly episodic memories
-
Explains flat retrograde amnesia
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What about temporal gradients?
- Older episodic memories often become
semantic and so don’t need the
hippocampus for retrieval
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The hippocampus is an integrator of context and
recollective details of episodic memories
When we retrieve memories with more details,
the hippocampus is more active
R
Addis et al. (in press)
LTM: Role of the Prefrontal Cortex
• MTL not the only region involved in LTM
• Prefrontal cortex also play important role
• Summarized in the HERA model (Cabeza et al)
-
LTM: Role of the Prefrontal Cortex
• Encoding: Left Prefrontal Cortex
-
Hemispheric Encoding/Retrieval Asymmetry
-
LTM: Role of the Prefrontal Cortex
• Retrieval: Right Prefrontal Cortex
-
Important in processing supporting retrieval
- e.g., strategies used to search for a memory
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Post-retrieval processing, e.g., verification
-
Right PFC damage: Confabulation (“honest lying”)
- Often produce “memories” that are actually
composites of different real events and
aspects of semantic memory
- WHY?
- Compensation for lack of episodic detail
- Lack of verification
- Inability to inhibit responses
Supports the use of encoding strategies
Impaired frontal functioning: e.g., older adults:
- Tend to use shallow encoding strategies
- Show poorer performance on encoding tasks
Successful encoding shows greater activation of
left PFC (Wagner et al., 1998)
LTM: Role of the Diencephalon
•
Damage to regions such as dorsomedial thalamus
and mammillary bodies causes amnesia
- Similar to MTL amnesia
- Impaired explicit / spared implicit memory
•
Causes of damage:
- Alcoholism and thiamine deficiency:
Korsakoff’s syndrome
- Strokes
- Fencing foils (case N.A.) and snooker cues
(case B.J.) entering the brain via the nostril
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LTM: Role of the Diencephalon
•
Summary: Important memory dissociations
What role does the diencephalon play?
(Hodges and McCarthy, 1993)
• Short-term vs. long-term memory
-
• Explicit vs. implicit memory
-
Case P.S.: Stroke in DM thalamus
Severe retrograde amnesia
Link between frontal lobes (search strategies)
and posterior neocortex (stored memory traces)
Damage = disconnection syndrome
Can’t use search strategies to search through
memory traces
• Semantic vs. episodic memory
• Anterograde vs. retrograde memory
• Verbal vs. non-verbal memory
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