Memory

1
Memory

• Chris Rorden
• Anterograde Amnesia
• Short vs Long Term Memory
• Episodic vs Procedural Memory
• Confabulation

www.mricro.com
2
HM

• Severe epilepsy, treated with surgery to
  bilaterally remove medial temporal lobes.
• Operation 9/1953, 27 years old
• Tested 4/1955, age 29
• Reported date as 3/1953, age of 27
• No memories since operation
• IQ better than pre-op (112)
• Fewer seizures
• Profound failure to create new memories
• Cant find new home (after 10 mos.)
• Cant remember new people, names, tasks

3
HM

• Deficits
• Complete loss of episodic memory
• Events/People since operation
• Location of new home
• Rey figure copy but not recalled
• Semantic memory
• Language essentially frozen in 50s (Gabrieli et
  al. 1988)
• Exceptions ayatollah, rock n roll

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HM severe anterograde amnesia

• Anterograde amnesia since lesion
• Suggests encoding deficit
• Retrograde amnesia prior to lesion

anterograde
retrograde
Memory
1/9/1953
1945
1950
1955
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HM working memory

• Intact working memory
• Normal digit span (remembering numbers)
• Wickelgren (1968) showed rate of forgetting
  within normal range
• Unless interrupted (constant rehearsal)

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HM procedural memory

• Intact procedural memory
• Can learn new motor tasks
• Mirror tracing task (Milner 1962, 1965)
• Pursuit rotor tracing (Corkin, 1968)
• Implicitly familiar w testing equipment
• Anterograde amnesics can learn new piano pieces
  (Starr Phillips, 1970)

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HM implicit memory

• Perhaps procedural tasks tap implicit memory
  HM has deficit of explicit memory
• Milner et al (1968) showed HM learned Gollin
  incomplete picture task

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HM implicit memory

• HM has also implicitly learned Tower of Hanoi
  game (Cohen, 1984).
• Can not remember playing, but solves quickly.

Start Position
Goal 2 (2 moves)
Goal 10 (5 moves)
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Memento Amnesia in Film Noir

• Guy Pierce

• Sammy Jenkins

10
HM

• Temporally graded retrograde amnesia
• Old memories (childhood) OK
• Memories immediately before lesion lost
• Forgot death of favourite uncle in 1950
• Suggests consolidation takes time

Memory
1/9/1953
1945
1950
1955
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How long does consolidation require?

• Testing retrograde amnesia.
• HM photos of celebrities suggest retrograde
  amnesia spans decades, with more distant memories
  relatively preserved (Marslen-Wilson Teuber,
  1975)
• PZ Butters Cermak (1986)
• Wrote autobiography
• Test personal memories

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Medial Temporal Lobe Memory

• MTL patients
• Short term memory intact
• Old long term memory intact
• Suggests consolidation deficit
• Encoding deficit, retrieval intact
• See Warrington Weiskrantz for alternate view
• Unable to create new LTM
• LTM formation requires years?

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Anatomy

• Anterograde amnesia follows damage to medial
  temporal lobe or connected regions.
• MTL or diencephalic structures like thalamus and
  mamillary bodies
• E.G. NA had fencing foil in nose
• Accident in 1960
• Diencephalic damage
• Similar to HM, though less retrograde

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Anterograde Amnesia

• Similar deficits with damage anywhere in Papez
  circuit.

Fornix (Squires Patient) Mammillary
body (Korsakoff Patients)
Hippocampal formation - HM
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Hippocampus (T1 MRI)

• Folded shape seen in coronal image.
• Here healthy individual

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HMs lesion

• Surgeon report describes removal of entire
  hippocampus (Scoville Milner, 1957).
• Recent MRI (Corkin et al., 1997) study suggests
  posterior hippocampus is present (though
  atrophied).

Scoville Milner 1957
Corkin et al. 1997
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HMs lesion

• Corkin et al. (1997)
• bilaterally symmetrical
• medial temporal pole
• most of the amygdaloid complex
• most or all of the entorhinal cortex
• anterior half of hippocampal formation (dentate
  gyrus, hippocampus, and subicular complex)

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Memory primacy and recency

• People often remember the first few and last few
  items in long lists
• First words primacy most rehearsal
• Final words recency least interference
• Clearly easier you do not have to remember as
  long
• These are thought to reflect different processes

recall
1 2 3 4 5 6 7 8 9 10
Item Number
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Amnesics show no primacy effect

• Patients like HM remember last few words (when
  not interrupted)
• Recency effect intact
• Primacy effect gone no encoding benefit

recall
1 2 3 4 5 6 7 8 9 10
Item Number
20
Memory

• Are primacy and recency effects different
  processes
• Maybe recency is simply easier
• Evidence would come from patients who show an
  opposite pattern of effects
• Primacy intact
• Recency impaired
• These patients would provide a double
  dissociation

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Primacy and recency

• Short term (working) memory

Long term memory
recall
1 2 3 4 5 6 7 8 9 10
Item Number
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Patient KF

• Shallice Warrington (1970)
• Primacy effect intact
• Recency effect impaired
• Complements amnesic patients

recall
1 2 3 4 5 6 7 8 9 10
Item Number
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Potential Paradox
Can information get into long term memory if
there is no short term memory?

• Short term memory

Long term memory
recall
1 2 3 4 5 6 7 8 9 10
Item Number
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Does LTM require STM?

• According to Atkinson Shiffrin (1968)
• STM rehearsal leads to LTM
• Predicts that LTM will depends on STM
• Can not accommodate Shallice and Warringtons
  patient

Sensory (iconic) Memory
Short Term Memory
Long Term Memory
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Shallice Warrington (1970)

• S W suggest that short term and long term
  memory independent from each other.
• Short term memory not required for long term
  memory
• Very controversial model

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Baddeley working memory

• STM is encoded by system dedicated to input
• Verbal info phonological loop
• Visual info visuo-spatial scratchpad
• LTM is more modality independent

Phonological Loop
Visuo-Spatial Scratch pad
Phonological Loop
Long Term Memory
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A Implicit vs explicit memory

• MTL amnesics
• Explicit memory unable to create
• Implicit memory relatively intact
• So far single dissociation
• 2 possibilities
• Implicit/Explicit 2 independent systems
• Implicit simply easier, relies on residual
  processing of a single, partially damaged system
• Double dissociation would support claim of 2
  independent systems

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B Gabrieli et al. (1995)

• Patient MS
• 29 year old, right handed male
• Intractable epilepsy surgery removed right BA
  17,18, part of 19.
• Hemianopic (blind in left field)
• Compared to MTL amnesics and healthy controls.

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C Results

• Explicit memory task
• Shown 24 words, later shown 48 words (24 from 1st
  phase, 24 new foils) asked to say if words were
  previously seen.
• Amnesics poor.
• MS fine.

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D Conclusion

• Implicit memory word completion task
• Shown/Heard 24 words stick, later asked to
  complete 48 stems, 24 could be solved with items
  from 1st phase (sti__) and 24 unrelated stems
  (sta__).
• Healthy people show priming effect (faster if
  solution seen previously). This effect is much
  bigger if words were seen (physical match) rather
  than heard.
• Amensics show normal priming. Shows implicit
  memory.
• MS visual priming is no greater than auditory
  priming. Therefore, shows no extra benefit for
  physical match of stem and previously seen word.

Conclusion Double dissociation Explicit memory
has some distinct processing from implicit
memory. Conceptual priming intact in MS,
perceptual priming damaged
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Recollection vs Familiarity Memory

• Is implicit memory really preserved in MTL
  amnesics?
• Explicit tasks usually much harder
• Explicit Recall What was the picture I showed
  you earlier? Could have thousands of answers.
• Implicit Recognition Which of these two
  pictures did I show you only has two answers,
  and seeing the correct answer may jog memory.
• Is this a meaningful dissociation? (see Simons
  Spiers, 2003)
• Jon and YR have intact Recognition, but impaired
  recall
• Selective lesions to only hippocampus or fornix
• LG and PH have poor Recognition, even poorer
  recall
• Damage to hippocampus and surrounding
  parahippocampal regions
• Both groups show same pattern
• Not a double dissociation
• Harder task impaired for everyone

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Recollection vs Familiarity Memory

• Yonelinas et al. (2002) compare hypoxic patients
  (H, focal bilateral damage to hippocampus) to
  patients with unilateral but extensive damage to
  the hippocampus and surrounding tissue (H) and
  controls (C).
• For H group, recall correlated with recognition
  (below, left)
• Interaction between groups
• H poorer at familiarity (poor implicit)
• H poorer at recollection (poor explicit)
• Suggests Double dissociation is real

33
Semantic vs. episodic memory

• HM has impaired semantic and episodic memory
• Semantic Language frozen in 1950s (Gabrieli et
  al.)
• Episodic poor at remembering events.
• However, his lesions damage both hippocampus and
  surrounding temporal lobe.
• What about patients with more selective damage?

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A Graham et al. 2000

• Graham et al. suggest double dissociation
• Early Alzheimer's patients
• Semantic dementia patients

Alzheimers Patient Hippocampus atrophy
Semantic Dementia Temporal lobe atrophy
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B Test stimuli

• A Semantic naming task (phone)
• Correct answer phone.
• Memory tested 30 minutes later
• B Episodic memory task (perceptually identical)
• Correct answer I saw a phone earlier
• C Episodic memory task (perceptually different)
• Correct answer I saw a phone earlier.

36
C Semantic naming

• Semantic dementia patients have difficulty naming
  items.
• AD patients are fine at this task.

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D Episodic memory

• AD patients
• poor episodic memory.
• SD patients
• OK with identical items
• Poor with perceptually different (especially if
  unable to name item in picture naming phase).

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E Conclusions

• Suggests semantic and episodic memory may be
  separate.
• Hippocampal formation encoding episodic memories
• Temporal lobe storage of semantic memories.
• Additional support from Vargha-Khadem (1997), who
  reports 4 patients with selective hippocampal
  damage all show impaired episodic but intact
  semantic memory.
• Note all sustained hippocampal damage early in
  life, so does not necessarily generalize to adult
  brain.

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Memory Prefrontal Cortex (PFC)

• PFC damage results in
• Disinhibition
• Impulsiveness
• Disorganization
• Memory deficits
• Other deficits can hide memory problems
• Less pure than MTL amnesia

• Note oribtofrontal cortex subdivided
• Ventromedial PFC
• Ventrolateral PFC

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Memory structure (Squire Knowlton, 1994)

• Simplified from page 349 of Gazzaniga book

Declarative memory (explicit)
Nondeclarative memory (implicit)
Events (episodic) Experiences particular to
time/place MTL, PFC
Facts (semantic) World/word, language knowledge,
conceptual priming MTL, PFC
Procedural Motor, cognitive skills Basal ganglia,
cerebellum
Perceptual Perceptual priming Association cortex
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Interaction of different brain regions

• Lesions in animals and functional imaging suggest
  network of regions work together to encode
  memory.
• Beyond scope of neuropsychology course.

42
Spontaneous confabulation

• Confabulation syndrome
• Spontaneously produce confabulations (no need to
  make things up, no external trigger)
• Convinced of accuracy of their confabulations
• Acted on confabulations (indication of conviction)

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Double dissociation

• Spontaneous and provoked confabulation
  dissociate Schnider et al. (1996), Brain 119,
  1365-1375.
• Spontaneous confabulation
• Generate false memories without prompting
• Often whole gist of memory is false
• Provoked confabulation, false recognition
• Can be seen in healthy adults
• Accidentally report having seen word earlier in
  list if it is similar to previous word
• Errors with small details of overall story

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Example of spontaneous confabulator

• 58-year old woman
• Aneurysm of anterior communicating artery.
• Reported needed to go home to feed her baby
• Her baby was 30 years old

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Case 2

• 48 year old tax accountant
• Traumatic damage to orbitofrontal lobe
• Left hospital convinced taxi was waiting to take
  him to meeting
• Consistently thought he had business meeting

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Reflections

• Ideas tend to be internally consistent but
  inaccurate.
• Careful testing shows they are disoriented,
  confuse date and time.
• When confronted, often search for explanations
  but fail to adapt their ideas
• Patient in Berne convinced he was in Bordeaux.
• Admitted view from window inconsistent with
  belief.
• Did not change belief.

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• Most confabulations about present
• Plausible
• Traced to actual events
• Usually accurate regarding old memories
• Majority eventually stop confabulating despite
  permanent brain injury

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Eliciting confabulations

• Individual is asked if they saw an image before
  earlier in run.
• Do not report having seen image if you only saw
  it in a previous run.

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Eliciting confabulations

• Both amnesics and confabulators do poorly at
  remembering if they have seen an item before.
• Amnesics forget previously seen items.
• Confabulators report having seen an image from
  previous set in current set.
• Problem with context, not recognition per se.

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Anatomy of confabulations

• Patients who spontaneously confabulate tend to
  have orbitofrontal damage (aka damage to the
  ventromedial PFC).