Memory Consolidation A Summary PSY 506A 11.4.11 Molly Bisbee

Overview 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 H-trace 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 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 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?

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

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?

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

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