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 loss of episodic memory – Events/People since operation  Location of new home  Rey figure: copy but not recalled  Semantic 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

retrograde anterograde 4 1945 1950 1955

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.

8 Start Position Goal 2 (2 moves) Goal 10 (5 moves)

Memento – Amnesia in Film Noir

 Guy Pierce

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 Sammy Jenkins

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

10 1945 1950 1955

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.

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Fornix (Squire’s Patient) Mammillary body (Korsakoff Patients) Hippocampal formation - HM

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).

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Scoville & Milner 1957 Corkin et al. 1997

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

18 1 2 3 4 5 6 7 8 9 10 Item Number

Amnesics show no primacy effect

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

19 1 2 3 4 5 6 7 8 9 10 Item Number

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

Long term memory Short term (working) memory

21 1 2 3 4 5 6 7 8 9 10 Item Number

Patient KF

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

1 2 3 4 5 6 7 8 9 10 Item Number 22

Potential Paradox

Can information get into long term memory if there is no short term memory?

Long term memory Short term memory

23 1 2 3 4 5 6 7 8 9 10 Item Number

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. Implicit/Explicit 2 independent systems 2. 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 1 st 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 1 st 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.

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Conclusion Double dissociation Explicit memory has some distinct processing from implicit memory.

‘Conceptual’ priming intact in MS, perceptual priming damaged

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

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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 Hippocampus atrophy Semantic Dementia Temporal lobe atrophy 34

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 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:

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Ventromedial PFC

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Ventrolateral PFC 39

Memory structure (Squire & Knowlton, 1994)

 Simplified from page 349 of Gazzaniga book Declarative memory (explicit) Nondeclarative memory (implicit)

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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

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

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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 t

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

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