PS4529/30 Applications of Cognitive Neuroscience
Consensus View of Long-Term Memory ENCODING RETRIEVAL Seeing Word Hearing Word 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 l Indexing of episodes: exactly how is unknown l Necessary both for encoding and retrieval l Damage leads to dense retrograde and anterograde amnesia The frontal lobes l Strategic control over memory: exactly how is again unknown! l Damage leads to confabulations, delusions, heightened false memory, source amnesia The entire association neocortex l Representation of experienced content l Damage should lead to loss of specific content of prior episodes
CMF Retrieval Functions l Retrieval focus l Access to the records of attended information via a retrieval cue (by hippocampal pattern completion) l Inhibition of irrelevant information l Re-activation of episodic content (held in the neocortex) l Monitoring/evaluating retrieval products (prefrontally mediated)
Conways 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-related semantic knowledge Abstracted from specific experiences
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-related semantic knowledge Abstracted from specific experiences 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?
ERP correlates of retrieval from long-term memory
Stimuli Time 0.10.20.40.30.50.700.6 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 TIME Visual Auditory MTL Encoding MTL Retrieval
Do ERPs reveal 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 l Studied SEEN items l Studied HEARD items l Unstudied NEW items ERP retrieval effects for each sensory modality:- l SEEN – NEW difference l 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 retrieval begins…
ERP 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 Consolidation Mechanisms Attentional Control EncodingStorageRetrieval Attentional Control Semantic Records Perceptual Records Binding Context Semantic Records Perceptual Records 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?
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 EEE R E R E RRR 3-Phase Dual-task Paradigm
Stimulus-Onset Asynchrony (SOA) Encode time-line begins WILD Retrieve time-line begins Time controlled jitter Expt. 1 SOA range: 50-200msec Expt. 2 SOA range: 50-2000msec
Effect of ignoring retrieval cues Retrieval under full attention Retrieval under distracted attention LP effect minimal/absent under DA, replaced by F-N400 but 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?