Memory Consolidation
A Summary
PSY 506A
11.4.11
Molly Bisbee
Overview
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Definition
Standard model
MTT
Differences
Evidence
General Definition
• A process after initial encoding that is
critical to stable long-term memory
– Stabilizes memories
– Incorporates new information with old
Temporal Characteristics
• Cellular or synaptic consolidation
– Brief process lasting seconds or minutes
• Initial emphasis
• Systems consolidation
– Lasts weeks, months, or years
• Recent emphasis
Human Memory Systems
The Standard Model (STM)
• dispersed neocortical sites linked together by hippocampal
complex, where ensemble trace is rapidly created (via LTP or
the like)
– H-trace, or “index”, “binds” the dispersed C-traces,
allowing dispersed cortical sites to be reactivated together
• over time, C-traces link directly; intervention of H-trace
no longer needed, it fades away
– information content is the same whether or not Htrace is involved in retrieval
– Hippocampus plays same role in episodic and
semantic memory
STM
STM Problems
• Length of consolidation period
• Dissociations among episodic and
semantic memory
• Reconsolidation
Multiple Trace Theory
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H always involved in storage and retrieval of episodic memory
The H-C combination is the episode memory trace
H represents contextual component of episode
each re-activation/retrieval of a memory occurs in different
context and results in altered trace; expanded or strengthened H
trace and H-C links
• episodic and semantic memory must be considered separately
MTT
Similar to Standard Theory
• hippocampus automatically
encodes all attended
information
• H- traces are sparsely
encoded in distributed
representations
• these ensembles act as
pointers to the cortical
ensembles storing attended
information
Different from Standard Theory
• the H-C complex is the episode
memory trace; H serves not only
to bind elements in C, but also
as the repository of critical
episodic components
• each re-activation of a memory
occurs in a different context and
results in a new sparse,
distributed trace in H
• each such trace shares some of
the C representations
MTT asserts that H and C are both always involved in the storage and
retrieval of episodic memory, and that episodic and semantic memory must
be considered separately.
MTT Implications
• Aging episodic memories either forgotten or benefit from formation of
stronger, expanded, memory traces
• HC active during retrieval of episode memories of any age
• HC preferentially active in processing spatial/contextual material
• H plays different role in episodic and semantic memory
• Partial HC damage affects memories proportional to age/strength;
complete HC lesions will yield flat gradient of RA for episodic, but not
semantic memories
• Remote memories in amnesics should be generic in nature
• Older memories will have stronger, more distributed, traces in H
• Reactivating a memory should lead to updating and reconsolidation
HC active during
retrieval of recent
episode memories
HC active during
retrieval of episode
memories of any age
vs.
The evidence?
Left Hippocampus
Standardized signal
8
6
4
Recent
Remote
Rest
Sentences
2
0
-2
-4
-6
0
2
4
6
8
Time (secs)
10
12
14
16
18
Older memories will have
weaker, less distributed, (or
nonexistent) traces in H
vs.
Older memories will have
stronger, more distributed,
traces in H
The evidence?
Remote events
Foci of left hippocampal
activations across subjects
Recent events
Older memories
are represented
more diffusely
within
hippocampus
Reactivating a
memory should not
affect it
vs.
The evidence?
60
50
49.5
45.0
40
30
20
36.3
23.8
10
4.9
0
Reminder
0.5
No-Reminder Interference Control
Reactivating a memory
should lead to updating
and reconsolidation
Reactivating a memory
should reduce H
involvement
vs.
Reactivating a memory
should increase H
involvement
The evidence?
Repeated retrievals increase activation in hippocampus –
equivalently for recent and remote memories
Recent 2 > Recent 1, p < 0.05
L post HC
R phg
Remote 2 > Remote 1, p < 0.05
L post HC
R phg
Reactivation
• Memories can be reactivated either online
(during wake) or offline (during sleep)