PS4529/30PS4529/30ApplicationsApplicationsof Cognitiveof CognitiveNeuroscienceNeuroscience

Consensus View of Long-Term Memory

ENCODING RETRIEVAL

Seeing Word

Hearing Word

MTL

MTL

MTL

MTL

A Specific Example

• The constructive memory framework (CMF)• Schacter, DL, Norman, KA, and Koutstaal, W.

(1998). The cognitive neuroscience of constructive memory. Annual Review of Psychology, 49, 289-318.

• Invokes multiple brain regions• Some involved in encoding and retrieval• Some involved in either encoding or retrieval

• Comprising multiple functions that must interact dynamically with one another

CMF Neuroanatomy

• The hippocampal formation ‘Indexing’ of episodes: exactly how is unknown Necessary both for encoding and retrieval Damage leads to dense retrograde and anterograde

amnesia

• The frontal lobes Strategic control over memory: exactly how is again

unknown! Damage leads to confabulations, delusions, heightened

false memory, source amnesia

• The entire ‘association’ neocortex Representation of experienced content Damage should lead to loss of specific content of prior

episodes

CMF Retrieval Functions

Retrieval ‘focus’

Access to the records of attended information via a retrieval cue (by hippocampal pattern completion)

Inhibition of irrelevant information

Re-activation of episodic content (held in the neocortex)

Monitoring/evaluating retrieval products (prefrontally mediated)

How Many Experiences Have you Had?

1

10

100

1000

10000

100000

1000000

10000000

100000000

1000000000

HOUR DAY WEEK MONTH YEAR DECADE

TIME

Num

ber

of e

piso

des

(log)

Conway’s SMS Model

The Self Memory System (SMS) has two principle components:-

• 1. Autobiographical knowledge base– organised specifically to support our

sense of self

• 2. The (working) Self– comprises a goal hierarchy, and various

other internal mechanisms

Autobiographical Knowledge Base

‘Self’

Episodic Memory tied to specific experiences

(e.g. the CMF)

Retrieval

Consolidation

Encoding

Self-relatedsemantic knowledge

Abstracted from specificexperiences

Goal Hierarchy

Take a peek inside yourself…

Conceptual Self

Self

Autobiographical Knowledge Base

semantic knowledge

Episodic Memory(CMF)

Key point: the SMS system is ‘goal-driven’

The SMS greatly extends the CMF

• Conway: “all daily experiences are destined to be forgotten”– Unless they support longer-term goals

• In the short term, accurate memories are vital– Where did I leave my keys

• In the long-term, coherence (between goals) is vital– The ‘Husband-Hermit’ or ‘Saint-Sinner’ dilemma

SMS Goals• Short term (e.g. daily)

– Take the car for a service…– Find the keys…– Post the letter…

Overriding principle: accuracy!

• Long-term– Get a job– Learn how to drive– Buy a house– Become a solitary religious hermit– Be a loving husband

• Overriding principle: coherence

But: there is an accuracy-coherence trade-off!

Potential for conflict!

How is the trade-off achieved?

• The goal hierarchy maintains a stable and coherent set of short and long term goals

Goal Hierarchy

Eat and drink (everyday)Keep warm (everyday)

Have a conversation (most days)Watch TV (particular times)

Find the car keys (in 5 minutes)Avoid tripping up (when I walk)

Post the letter (sometime today)Dentist appointment (this week)

Revise (next month)Obtain graduation ball tickets (next few

months)Find a less annoying partner (yesterday!)

Get a 2:1 (next couple of years)Loose weight (before going on holiday)

The SMS: key points

• New memories are not formed ‘automatically’ from our experiences– But, experiences are always encoded (e.g. as per the CMF).

• An ABM is formed (and retrieved) only when the (working) self interacts with the autobiographical knowledge base

– Such interactions are entirely goal-driven

• Hence, specific experiences will be forgotten unless they relevant to a goal - within the goal hierarchy

• Stable self-image emerges from the coherence imposed by the goal hierarchy, perhaps at the expense of accuracy

Autobiographical Knowledge Base

‘Self’

Episodic Memory tied to specific experiences

(e.g. the CMF)

Retrieval

Consolidation

Encoding

Self-relatedsemantic knowledge

Abstracted from specificexperiences

Is this: (1) A scientifically acceptable and (2) A forensically useful model?

Can ERPs reveal exactly what is happening in the brain while people remember their past?

cueonset

Ecphory/inhibition

MonitoringRetrieval Perception/attention

Patterncompletion/

Binding

‘selective attention’

Stimuli

Time 0.1 0.2 0.40.3 0.5 0.70 0.6

Constructive Memory Framework

Focussed Search

Retrieve / Inhibit Monitor

Stimuli

0Time - 1 3 4 65 7 92 8

Retrieval success!!Retrieval failure

ERP correlates of retrieval from long-term memory

Stimuli

Time 0.1 0.2 0.40.3 0.5 0.70 0.6

Ecphory?

Monitoring?

Implicit Memory?

Familiarity?

Donaldson, Allan and Wilding (2003)Mecklinger (2000)Rugg and Wilding (2000)

F-N400

LP effect

RF effect

Content only (versus failure)

Content and Context

LP effect magnitude X content relation

Using ERPs to investigate the notion of encoding-retrieval overlap

1. By manipulating the content of what is encoded and retrieved.

2. By manipulating the timing of encoding and retrieval, to make them coincide.

1. Manipulating Content

• Operationally define different classes of study episode

• Record EEG when instances of each class of episode are recollected

• Form ERPs to each class of recollected episode

• Contrast the magnitude and topography of ERPs for each class of recollected episode

Encoding and Retrieval in vivo…

Olfactory (Gottfried et al, 2004)

and within ‘sensory domain’ too (Woodruff et al., 2005)

MTL

Encoding

MTL

Retrieval

TIMEVisual

Auditory

MTL

Encoding

MTL

Retrieval

Do ERPs revealDo ERPs revealmodality specific retrieval processes?modality specific retrieval processes?

• Subjects SAW and HEARD words at study

• Performed a word-stem (e.g. MOT__) cued recall task

• ERPs were formed to stems completed with Studied SEEN items Studied HEARD items Unstudied NEW items

• ERP retrieval effects for each sensory modality:- SEEN – NEW difference HEARD – NEW difference

Allan, Robb and Rugg (2000), Neuropsychologia, 38 1188-1205.

No!ERPs are insensitive to

differences in modality at retrieval

Recall auditory episodeRecall visual episode

As retrieval ends…

As retrievalbegins…

ERP Modality Experiment: ConclusionsERP Modality Experiment: Conclusions

• Multiple retrieval processes, active at different times– Onset ~ 0.5s after retrieval cue!

• Retrieval of ‘visual’ and ‘auditory’ episodes involves common processes. No evidence for modality specific retrieval processes.

• ERPs reflect a ‘core component’ of retrieval? – Changes in neocortical activity driven by the

Hippocampus during early stages of retrieval (prior to modality specific activations)?

– Or: attention to retrieval products?

Episodic Memory Mechanisms

ConsolidationMechanisms

AttentionalControl

Encoding Storage Retrieval

AttentionalControl

SemanticRecords

PerceptualRecords

Binding

ContextSemanticRecords

PerceptualRecords

Binding

Context

• Gain precise control over the relative timing of events experienced in different modalities.

• Stress the system by forcing it to handle very rapidly changing inputs, to reveal what the temporal limits are.

• Examine resulting performance behaviourally

• And use high temporal resolution neurophysiological data to expose the underlying functional states

2. Can we simultaneously encode and retrieve?

Allan and Allen (2005), Journal of Neuroscience, 25, 8122-9130.

Does encoding temporarily stop when retrieval occurs?

How Many Experiences Have you Had?

1

10

100

1000

10000

100000

1000000

10000000

100000000

1000000000

HOUR DAY WEEK MONTH YEAR DECADE

TIME

Num

ber

of e

piso

des

(log)

Visual

Auditory

+/- 200msec period of stimulus onset asynchrony (SOA) jitter, in 10 time bins (41 – 194msec)

E == encode (animacy task)

R == retrieve (old/new recognition)

Key

Phase 1

Phase 2

Phase 3

E E E

R

E

R

E

R R R

3-Phase Dual-task Paradigm3-Phase Dual-task Paradigm

Stimulus-Onset Asynchrony (SOA)

Encode time-line begins

WILD

Retrieve time-line begins

Time controlled ‘jitter’

Expt. 1 SOA range: 50-200msecExpt. 2 SOA range: 50-2000msec

0

10

20

30

40

50

60

70

80

% c

orr

ec

t

Full Hit 71.85 62.66

DA Hit 72.03 49.38

Full CR 79.21 71.04

DA CR 76.88

phase 2 phase 3

Dual-task Performance (Expt. 1)Dual-task Performance (Expt. 1)

Effect of ‘ignoring’ retrieval cues

Retrieval under full attention

Retrieval under distractedattention

LP effect minimal/absent under DA, replaced by F-N400but no reliable topographic differences (Allan and Allen, 2005)

• Encoding stabilised at a temporal gap of ~600msec(see Expt. 2), i.e. just as the ERP effect begins.

– retrieval cue processing is complete.– neocortical trace reactivation has commenced.– so ‘automatic’ encoding of experience can begin again?

• Retrieval shows a subtle alteration towards reliance on familiarity

• Mode-shifting between encoding and retrieval in human memory is relatively sluggish

•The LP effect may reflect the attention paid to retrieval products, not the representational nature of those products

Conclusions

Next week -

Do these ERP effects objectively indicate the presence / absence of an episodic memory?