Episodic Memory

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Episodic Memory

• Episodic memory is the form of memory that
  allows an individual to recollect happenings from
  his or her past. (Tulving, 1992)?
• Where does EM fit in the taxonomy of Memory
  systems?

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Old Taxonomy of memory(Tulving 1972)?
Types of memory working long-term (shor
t-term)? explicit, declarative implicit
episodic semantic procedural perceptual
(event) (fact) representional Tulving,
Endel (1972). Episodic and semantic memory.
Organization of memory. In E. Tulving and W.
Donaldson. New York, Academic Press.
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Baddeley's (2000, 2003) memory model
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2 senses of 'episodic'

• 1. Episodic memory task
• 2. Episodic memory system

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1. The episodic memory task

• If it is not possible to retrieve information
  other than through recollecting a specific
  episode, a task is considered an EM task.
• By this rule, conventional recall of and
  recognition tasks, in which the rememberer must
  produce the name, or identify as 'old', a copy of
  an item encountered on an earlier occasion in a
  particular situation, are classified as
  episodic. (Tulving, 1983, 55)?

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Varieties of EM tasks

• Free recall Name the items in the study list
• Seriall recall Name the items in their serial
  order
• Paired-associate task What was the associate of
  the presented item?
• Cued recall task Name the item from the list
  which is prompted by a retrival cue (e.g., rhyme,
  category)?
• Yes/No recognition task Have you seen item X
  before?
• ...
• --gt Each of these tasks can be described in
  terms of the subject's earlier personal
  experience. This is why they are classified as
  episodic memory tasks. (Tulving, 1992)?

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2. Episodic memory system

• What is the neurocognitive system sustaining EM?
• Such a neurocognitive system is supposedly
  specific to EM as opposed to other memory
  systems, e.g., semantic or procedural memory.
  Only by virtue of an intact brain system
  specialized for this purpose can we access EM.

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Time-scales of EM

• The typical EM tasks only tap on specific
  sections of the entire EM system, namely those on
  a micro- or medium time scale.
• The entire system also includes more long-lasting
  EM such as Long-term episodic memory sometimes
  called autobiographic memory, i.e., memories of
  (significant) personal past experiences such as
  1st schoolday, marriage, accidents, etc.

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The novel Episodic Memory System

• The old EM Model of Tulving has been revised in
  the course of time. The change was conditioned,
  among others, by studies on young patients with
  anterograde amnesia due to hippocampal pathology,
  who, nevertheless, were able to acquire
  declarative (semantic) knowledge
• Endel Tulving and Hans J. Markowitsch (1998)
  Commentary. Episodic and Declarative Memory. Role
  of the Hippocampus. Hippocampus 8, 198-204.
• Vargha-Khadem, F., Gadian DG, Watkins KE,
  Connely, A, Van Paesschen W., Mishkin, M. (1997)
  Differential effects of early hippocampal
  pathology on episodic and semantic memory.
  Science, 277, 376-380.

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Affected Episodic MemorySpared Semantic Memory

• Such a dissociation argues against a unitary view
  of hippocampus as subserving both episodic and
  semantic M. (as, e.g., proposed by Squire)?
• Tulving claims, with Varga-Khadem, that the
  hippocampus is solely concerned with EM whereas
  other parts of the Medio-temporal lobe are
  associated with declarative memory.
• He comes up with a new division between
  declarative, semantic, and episodic M.

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The SPI Model (Tulving and Markowitsch 1998)?
SSerial encoding Pparallel storage Iindependent
retrieval - Information gets into the EM system
only via SM (serial) - Information is both
stored semantically and episodically
(parallel)? - Informatin from both systems are
independently retrieved. Due to the implicature,
there is no way in which SM could be affected but
EM is not however, EM can be affected but SM
is not
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Similarities between declarative and episodic
memory
12 common features
9 specific features

• Semantic Declarative Episodic Memory

Declarative Memory shares 12 properties with
Episodic M 9 properties are unique to Episodic M
Semantic M is the language-related form of
Declarative M.
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12 common features of declarative and EM. Both
systems are...

• 1. large and complex, highly structured
• 2. take multimodal input
• 3. characterized by similar, fast, encoding OP
• 4. representational,
• 5. propositionally describable, symbolic
• 6. have truth value
• 7. accessible and expressible flexibly
• 8. serve as basis for inferences

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12 common features continued...

• 9. Ops are context-specific
• 10. Ops are cognitive (not behavioral)?
• 11. products can be but do not have to be
  expressed in overt behavior
• 12. interact closely with other brain/behaviour
  systems (language, emotion, reasoning)?

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Uniqueness of EM9 distinctive features. EM is...

• 1. a system that makes possible remembering of
  previous experiences
• 2. The only form of memory oriented towards the
  past
• 3. associated with autonoetic consc awareness
• 4. includes but goes beyond (sem.) knowledge of
  the world remembering gt knowing
• 5. its relations to semantic M are
  process-specific (see Serial Parallel
  Independent, SPI-Model)?

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9 distinctive features continued

• 6. develops later than semantic M in young
  children (ca. 4 yrs)?
• 7. is more vulnerable (change, amnesia, age)?
• 8. probably unique to humans (?)?
• 9. associated with selective and unique cortical
  activity

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Memory systems for Sem M and Dec M

• EM
• Hippocampus
• Frontal Lobes, esp. right-frontal for specific
  episodic retrieval mode or retrieval attempt

• Decl M
• Rest of Medio-Temporal Lobe,e.g., perirhinal
  cortex

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The scope of Episodic Memory

• It took biological evolution a long time to build
  a time machine in the brain, and it has managed
  to do it only once, but the consequences have
  been enormous By virtue of their mental control
  over time, human beings now wield powers on earth
  that in many ways rival or even exceed those of
  nature itself. It is difficult to imagine a
  marvel of nature greater than that. (Tulving
  2002, p 20).

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Episodic MemoryAn event-related functional
neuro-imaging perspective

• Michael D. Rugg and Richrd N.A. Henson (2002), In
  n Amanda Parker, Edward L. Wilding, and Timothy
  J. Bussey (Eds.), The cognitive neuroscience of
  memory. Encoding and retrieval. Psychology
  Press.3-37

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Event-related fMRI (efMRI)?

• efMRI allows for detecting the brain's response
  to brief stimuli, the 'events'.
• It detects the Blood Oxygenation Level Dependent
  (BOLD) haemodynamic response to neural activity.
• Spatial resolution millimetres
• temporal resolution hundreds of milliseconds

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Main Experimental Paradigm

• Yes-No recognition task
• Learning phase Subjects in the scanner are
  presented with a list of words
• Test phase Subjects are presented with a new
  list including 'old' words but also 'new' words.
  Their task is to indicate which of the words are
  'old' and which are 'new'
• During learning and test, their brain is scanned
  and regional blood oxygenation level is assessed

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3 possible confounds

• 1. Preretrieval vs. Postretrieval processes
• Preretrieval attempt to use a cue to retrieve
  info
• Postretrieval cognitive Ops after retrieval,
  e.g., maintenance in WM or evaluation
• 2. Process Impurity
• Hardly any retrieval task is process-pure, e.g.,
  performance on word-stem cued recall is the
  result of both Episodic M and implicit M
• 3. Item- vs. State-related brain activity
• Item-specific Activation reflects properties of
  the S
• State-specific Activation reflects general
  engagement in a particular task

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3 possible confounds

• -gt Problem Due to these confounds, one can never
  be sure what has caused activation in a
  particular brain area
• However, through efMRI, these confounds have been
  diminished

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Research Questions and procedures

• Which brain areas support Episodic M?
• Which are engaged in successful retrieval vs.
  Retrieval attempt?
• Which are engaged in distinguishing old vs. new
  words?
• Are there different sites for Remember/Know?
• Procedure Yes/No recognition task
• Variant Yes/No task with 'Remember' vs.
  'Know'-judgements
• Remember whether a word was judged old on the
  basis of recollection of some aspect of the study
  episode (context)?
• Know whether it was judged old solely on the
  basis of an acontextual sense of familiarity

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Brain regions sensitive to retrieval success in
Episodic Memory

• 1. Prefrontal Cortex
• 2. Medio-temporal Cortex (Hippocampus, limbic
  system)?
• 3. Parietal Cortex

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Main regions sensitive to retrieval success in
recognition studies

• 1. Left-anterior Prefrontal Cortex (PFC), Brodman
  Area (BA 10)?
• 2. left inferior and superior parietal cortex (BA
  39/40)?
• 3. precuneus (BA 7/19/31) (part of the limbic
  system, above the subparietal sulcus)?

http//spot.colorado.edu/dubin/talks/brodmann/bro
dmann.html
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Other regions sensitive to retrieval success in
recognition studies

• 4. right anterior PFC (BA 10)?
• 5. left and right dorsolateral PFC (BA 9/46)?
• 6. left ventrolateral PFC (BA 47)?
• 7. right inferior and superior parietal cortex
  (BA 39/40)?
• 8. posterior cingulate (MTL) (BA 23/31)?

http//spot.colorado.edu/dubin/talks/brodmann/bro
dmann.html
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Functional significance of activation

• Prefrontal Cortex, left anterior PFC (BA 10)
• More active for 'remember' than for 'know'
  responses for correctly recognised old items
• In this area, too, related 'lures' (semantically
  similar new words) are correctly rejected
• --gt this brain area governs successful retrieval
  of stimuli with a highly episodic character.
• In other studies, left anterior PFC is also
  active when requesting a 'source' judgement for
  new items.

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Functional significance continued

• Prefrontal Cortex, right anterior PFC (BA 10)
• According to Tulving (Tulving Markowitsch
  1998), right anterior PFC is active when the
  brain is in the 'retrieval mode' 'a mental state
  in which environmental events are treated as
  retrieval cues, and retrieved episodic memories
  are experienced auto-noetically' (i.e.,
  consciously)?
• --gt rather state-related, not item-related
• Alternatively both item-related and active in
  retrieval success
• also engaged in post-retrieval processes correct
  classified old words instigate a delayed
  long-lasting positive wave over the right frontal
  scalp

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Functional significance continued

• Prefrontal Cortex, right anterior PFC (BA 10)
• Problem Right anterior PFC shows atypical ERP
  responses, esp. delayed response latencies (after
  3s) and prolonged time-course of activation.This
  pattern has been called 'right frontal ERP
  old/new effect'

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Functional significance continued

• Dorsolateral PFC (BA 9/40)?
• active when task demands exceed simple
  recognition, e.g., introspective judgements on
  recognition decisions (low vs. High confidence)
  are requested or judgement true/false,
  irrespective of old vs. New items
• active in correct rejection of new words having
  been assembled from parts of old words
• --gt responsible for post-retrieval processes
  including monitoring

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Functional significance continued

• 2 different kinds of retrieval processes
• 1. left anterior PFC (BA 10)?
• active in successful retrieval of old words
• 2. Dorsolateral PFC (BA 9/40)?
• operates on the products of a retrieval attempt
  regardless of the amount or the nature of the
  information retrieved (old and new)?

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Functional significance continued

• left ventrolateral PFC (BA 47)?
• --gt sensitive for encoding of semantic and
  phonological stimuli
• --gt engaged in successful cue processing, if cues
  receive a sufficiently full semantic analysis
• --gt task specific engaged in direct recognition
  but also in indirect priming memory

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Functional significance continued

• Lateral and Medial Parietal Cortex (BA 39/40)?
• mainly left-lateralized, mainly in the inferior
  part (BA 40) than in the superior part (BA 7,
  parietal gyrus)?
• more active for remember gt know judgements
• --gt correlate of successful recognition of items
  with episodic character, irrespective of
  retrieval task
• In ERP studies, this correponds to 'left parietal
  old/new effect' which consists in a positive
  shift after 400-500 ms post-stimulus and which is
  maximal over the left-parietal scalp

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Functional significance continued

• Medial Parietal Cortex (BA 40)?
• well-recognized role in visual imagery if this
  area is active in successful recognition, this
  proves the visual demands of visual imagery in
  episodic memory retrieval processes

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Functional significance continued

• Medial Temporal Lobe (MTL)?
• Only 3 of the many efMRI studies report
  retrieval-related activation of the hippocampus
  and adjacent medio-temporal cortex, esp. for
  items likely to have exhibited strong episodic
  memory.
• --gt hippocampal activity is related to (strong)
  episodic M

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Functional significance continued

• (MTL), Hippocampus
• Contradiction why is the hippocampus not
  generally involved in these episodic M tasks?
• --gt the standard Yes/No recognition task is NOT
  process-pure, i.e., recollection of old items can
  be mediated by acontextual general facilitatory
  effects without hippocampal activation (2nd
  picture blue)which is especially geared to
  contextual information in episodic recall
• Familiary is processed in the perirhinal cortex
  (ventral and anterior to hippocampus, 2nd
  picture pink)?

http//research.psychol.cam.ac.uk/csnlab/index_fi
les/research.htm
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Functional significance continued

• (MTL), Hippocampus
• Contradiction why is the hippocampus not
  generally involved in these episodic M tasks?
• --gt could be a restriction of efMRI to detect
  such metabolic changes
• --gt could be that hippocampus is involved in both
  encoding ('new' words) and retrieval ('old'
  words) so that no difference in activation is
  found and hence hippocampus does not figure
  prominently in these kinds of tasks although it
  is actually highly involved

http//research.psychol.cam.ac.uk/csnlab/index_fi
les/research.htm
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References

• Baddeley, Alan D. (2000) The episodc buffer a
  new component of working memory? Trends in
  Cognitive Sciences, 4, 417-423.
• Baddeley, Alan D. (2003) Looking back and
  looking forward. Nature Reviews Neuroscience, 4,
  829-839.
• Rugg, Michael D. And Henson, Richard N.A. (2002)
  Episodic memory retrieval An (event-related)
  functional neuroimaging perspective. In Amanda
  Parker, Edward L. Wilding, and Timothy J. Bussey
  (Eds.), 3-37
• Tulving, Endel (1983) Elements of episodic
  memory. Oxford Clarendon Press.
• Tulving, Endel (1992) Episodic memory. In Larry
  Squire (ed.), Encyclopedia of learning and
  memory. NY Macmillan Publishing Group, 161-63
• Tulving, Endel (2002) Episodic Memory From Mind
  to Brain. Annual Review of Psychology, 53 1-25.