1. Memory Consolidation
A Summary
PSY 506A
Molly Bisbee

2. Overview
Definition
Standard model
MTT
Differences
Evidence

3. General Definition
A process after initial encoding that is critical to stable long-term memory
Stabilizes memories
Incorporates new information with old

4. Temporal Characteristics
Cellular or synaptic consolidation
Brief process lasting seconds or minutes
Initial emphasis
Systems consolidation
Lasts weeks, months, or years
Recent emphasis

5. Human Memory Systems

6. 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 H-trace is involved in retrieval
Hippocampus plays same role in episodic and semantic memory

7. STM

8. STM Problems Length of consolidation period
Dissociations among episodic and semantic memory
Reconsolidation

9. Multiple Trace Theory
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

10. 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.

11. 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

12. HC active during retrieval of episode memories of any age
HC active during retrieval of recent episode memories
HC active during retrieval of episode memories of any age
vs.
The evidence?

13. Older memories will have stronger, more distributed, traces in H
Older memories will have weaker, less distributed, (or nonexistent) traces in H
Older memories will have stronger, more distributed, traces in H
vs.
The evidence?
Remote events
Recent events
Foci of left hippocampal activations across subjects
Older memories are represented more diffusely within hippocampus

14. Reactivating a memory should lead to updating and reconsolidation
Reactivating a memory should not affect it
Reactivating a memory should lead to updating and reconsolidation
vs.
The evidence?

15. Reactivating a memory should increase H involvement
Reactivating a memory should reduce H involvement
Reactivating a memory should increase H involvement
vs.
The evidence?
R phg
L post HC
Recent 2 > Recent 1, p < 0.05
Remote 2 > Remote 1, p < 0.05
Repeated retrievals increase activation in hippocampus – equivalently for recent and remote memories 15

16. Reactivation
Memories can be reactivated either online (during wake) or offline (during sleep) 16