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Consolidation
A time-dependent process by which a new memory becomes stabilized after initial acquisition.
Cellular/synaptic consolidation.
Occurs within first few hours after learning. Involves changes to synaptic connectivity
Systems consolidation
May take months or years to complete. Gradual establishment of memories in neocortex, independent of hippocampus.
MULLER & PILZECKER (1900)
Introduced term “consolidation” – Memories are initially fragile and sensitive to disruption (interference) Over time they become strengthened and resistant to interference and are integrated into a network of pre-existing memories.
ROLE OF SLEEP IN CONSOLIDATION: DEBATE
Passive protection against interference or active consolidation? 1. Temporary protection against interference => no lasting benefit 2. Protects against interference so consolidation can proceed more efficiently than during wakefulness => lasting benefit 3. Active consolidation of declarative memories => lasting benefit.
SLEEP AND CONSOLIDATION •Ellenbogen et al. (2006)
Sleep following learning of AB pairs (e.g., BLANKET-VILLAGE) protected memory against interference from AC pairs (e.g., BLANKETRUBBER).
4 groups. Group 1 learned AB, slept and then was tested. Gorup 2 learned AB, slept, learned AC and then tested on AB. Group 3 and 4 did the same thing but stayed awake
STANDARD MODEL OF CONSOLIDATION
Experience initially encoded in parallel in hippocampus and cortical areas. Reactivation of hippocampal network reinstates the activity in cortical networks. Repeated replay of original experience across hippocampal-cortical networks leads to strengthening of cortico-cortical connections… …allowing new memories to become independent of hippocampus and integrated with pre-existing cortical memories.
DISRUPTION TO CONSOLIDATION- 3 things
Can occur as a result of: Interference from new learning (Muller & Pilzecker, 1900) Electroconvulsive shock (ECS) => memory impairment if given immediately after training, but not at a later stage (Duncan, 1949). Similarly, injection of protein synthesis inhibitors after memory acquisition => memory impairment in non-human animals (Nader, 2000)
Is consolidation the end of the process? Evidence that reactivation may destabilize memory again
ECS= electric convulsion shock
Misanin, Miller & Lewis (1968): reactivated a consolidated memory (fear of white noise that had been paired with footshock in rats) – ECS given after reactivation of the memory => disrupted memory – No disruption to memory when ECS given without memory reactivation
White noise played+ECS= disruped memory, rats no longer feared the white noise
No white noise+ECS= rats still afraid of white noise
RECONSOLIDATION HYPOTHESIS
Reactivation (a “reminder”) returns memory to a fragile (“labile”) state, similar to the state it is in when first acquired Memory then needs to be “reconsolidated” to stabilize it again While in this fragile state it is vulnerable to disruption: modification or even unlearningHow can disruption to reconsolidation be demonstrated experimentally in humans?
RECONSOLIDATION IN HUMAN MEMORY? ECS
ECS in patient studies: Rubin (1969): Patients suffering from obsessivecompulsive disorder (OCD) or hallucinations ECS administered when patients focused on their compulsions => alleviation of symptoms ECS during anaesthesia => no reduction in symptoms
Reactivation of the memory +ECS= changed memory
RECONSOLIDATION IN HUMAN MEMORY? DRUGS
Drugs in patient studies: Brunet et al (2008): Post-traumatic stress disorder (PTSD) patients wrote about their traumatic experiences
Patients given propranolol had lower heart rate and skin conductance measures than those given placebo.
CON= there was no group with drug+NO memory reactivation so cannot conclude that reactivation led to memory disruption
Also did not measure physiology before and did test px on their memory again
RECONSOLIDATION IN HUMAN MEMORY? SOME CHALLENGES
Squire, Slater, & Chace (1976): ECS only effective in disrupting new memory (for words and pictures), NOT when memory was reactivated
Why? High vs low emotional arousal
What are the problems with investigating reconsolidation in humans? Ethical Issues
Is it possible to disrupt reconsolidation with new learning (as we can with consolidation), rather than ECS or drug treatments?
WALKER, BRAKEFIELD, HOBSON & STICKGOLD (2003): MOTOR SKILL LEARNING
Finger-tapping task: 5-element sequence (e.g., 4-1-3-2-4) Repeated tapping for 30s, then 30s rest, for 12 trials Some groups learned 2nd sequence on Day 2
1. Overnight improvement in speed and accuracy when sequence tested on Day 2: consolidation 2. Learning 2nd sequence (S2) on Day 2 did not interfere with memory for S1 when tested on Day 3, which showed memory enhancement 3. But brief rehearsal (“reminder”) of S1 on Day 2 immediately before learning S2, impaired memory for S1 on the Day 3 test: reactivation => disruption of reconsolidation
L= list T= test. Px slept between days so helped ith memory
WALKER AT AL. (2003) POS AND CONS
First convincing evidence for reconsolidation effects in human memory: using new learning as amnestic treatment not involving emotional arousal But: Hardwicke, Maqi, and Shanks (2016) failed to replicate Walker et al’s finding of a reconsolidation effect in procedural memory 4 direct replications, inc using original software 3 conceptual replications
POTTS AND SHANKS (2012)
•Learning Finnish words on Day 2 impaired memory for Swahili words learned on Day 1 when there was no reminder test (Bars 3 and 4) •But reminder testing, far from disrupting List 1 memory, immunized it against interference: memory was as good in the group who had a reminder followed by interference as it was in the group who had the reminder test alone (Bars 1 and 2)
English and Swahili word pairs, px asked to recall the Swahili
L"2 had the same English words but with Finnish translation
R+= reminder given
I+= interference given
NECESSARY CONDITIONS FOR RECONSOLIDATION?
Potts & Shanks (2012): no evidence of disruption to reconsolidation in vocabulary-learning task in contrast, testing protected memory against interference Some researchers (e.g., Forcato et al., 2009, Hupbach et al., 2007) suggest that only a brief (or incomplete) “reminder” will allow modification of the memory to occur, not a full retrieval
HUPBACH ET AL. (2007): A “SUBTLE REMINDER” LEADS TO MEMORY UPDATING
On Day 1, participants learned a set of objects placed in a blue basket. Blue basket briefly mentioned on Day 2 (the “subtle reminder”) before learning of a new set of items. Test on Day 3
No difference in total recall between groups Reminder group showed more intrusions of List 2 into List 1 –“updating” of List 1 • Reconsolidation as mechanism for incorporating new information into existing memories?
Intrusion= recalled the object for the wrong day. eg said it was fro day 1 but it was learned in day 2
MEMORY UPDATING IN THE MISINFORMATION PARADIGM EYE Witness Testimony
Chan, Thomas, & Bulevich (2009) Younger and older adults more susceptible to misinformation when it was preceded by a recall test. “Retrieval enhanced suggestibility” (RES).
witness>test> misinformation>test
Does taking a test before receiving misinformation eliminate susceptibility to misinformation?
Chan & LaPaglia (2013)
Taking an initial cued recall test before hearing the misinformation led to greater susceptibility to the misinformation Evidence for overwriting of original memory? 48-hour delay between test and misinformation => no impairment (reconsolidation window closed) 48 hours between video and session with both test and misinfo => impairment, consistent with reactivation making memory malleable Source confusion? Recognition test allowed answering with original or later information. Testing => more misinformation, but effect was smaller.
Still unclear how you get this effect
What did subsequent studies of Chan and LaPaglia find
Subsequent studies have produced mixed findings. LaPaglia and Chan (2013, 2019): form of misinformation important? Narrative => retrieval increased suggestibility Questions => retrieval led to less suggestibility
RECONSOLIDATION IN HUMAN MEMORY: SUMMARY
Idea that consolidation leads to a permanently stable memory now seems unlikely However, evidence for reconsolidation effects in human memory has been inconclusive Some evidence that emotional memories may be modifiable via reactivation => potential clinical application (PTSD etc) Unclear under what conditions reactivation might lead to impairment of non-emotional declarative memories, or whether declarative memories can be erased or just updated
