4 Memory

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Memory •

Chris Rorden •

Anterograde Amnesia • •

•

Short vs Long Term Memory Episodic vs Procedural Memory

Confabulation

www.mricro.com

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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

Can’t find new home (after 10 mos.) Can’t remember new people, names, tasks

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HM  Deficits  Complete –

Events/People since operation Location of new home Rey figure: copy but not recalled

 Semantic –

loss of episodic memory

memory

Language essentially frozen in 50’s (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

1/9/1953

Memory

retrograde

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

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HM  Temporally – – –

Old memories (childhood) OK Memories immediately before lesion lost Forgot death of favourite uncle in 1950 Suggests consolidation takes time 1/9/1953

Memory

–

graded retrograde amnesia

1945

1950

1955

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How long does consolidation require?  Testing –

HM: photos of celebrities suggest retrograde amnesia spans decades, with more distant memories relatively preserved (MarslenWilson & Teuber, 1975)

 PZ – –

retrograde amnesia.

– 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 (Squire’s 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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HM’s 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

Corkin et al. 1997

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HM’s 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

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Item Number

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9 10

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Amnesics show no primacy effect like HM remember last few words (when not interrupted)  Recency effect intact  Primacy effect gone: no encoding benefit % recall

 Patients

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Item Number

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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

% recall

Long term memory

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Item Number

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Patient KF & Warrington (1970)  Primacy effect intact  Recency effect impaired  Complements amnesic patients % recall

 Shallice

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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

% recall

Long term memory

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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 Warrington’s 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: 1. 2.

–

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 –



LG and PH have poor Recognition, even poorer recall –



Selective lesions to only hippocampus or fornix 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

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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

Semantic Dementia

Hippocampus atrophy

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’.

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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 –

poor episodic memory.

 SD – –

patients 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

Memory structure (Squire & Knowlton, 1994)

 Simplified

from page 349 of Gazzaniga book

Declarative memory (explicit)

Nondeclarative memory (implicit)

Events (episodic)

Facts (semantic)

Procedural

Perceptual

Experiences particular to time/place

World/word, language knowledge, conceptual priming

Motor, cognitive skills

Perceptual priming

MTL, PFC

MTL, PFC

Basal ganglia, cerebellum

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.

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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

Example of spontaneous confabulator  58-year

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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).