Memory consolidation

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The broad definition of memory consolidation is the process by which recent memories are crystallised into long-term memory. The word "consolidation" is used to refer to different levels:

1. Molecular consolidation: The molecular process by which long-term conductivity of synapses is affected. Memory consolidation occurs after training (e.g. an exposition to a stimulus-response pair). Consolidation increases in strength over time with repetition. Maximum consolidation with minimum time investment is achieved by means of spaced repetition. Molecular consolidation requires protein synthesis.
2. Network consolidation: Many researchers believe that episodic memories are initially stored in the hippocampus and are slowly moved (or 'consolidated') into the neocortex. This process of consolidation begins during wakefulness and may be enhanced during sleep. Originally it was thought this happens during dreaming (Marr, 1971). However, new research indicates that the NREM phase of sleep is associated with that process (Hobbson, Stickgold, Buzsaki).

Main article: Sleep and memory consolidation

Reconsolidation

There is evidence in laboratory animals that recall puts memories into an unstable, labile state and that, after recall, the memory must be re-consolidated or it will be forgotten. Both consolidation and reconsolidation can be disrupted by pharmacological agents (e.g. the protein synthesis inhibitor anisomycin) and both require the transcription factor CREB. Recent research suggests that BDNF is required for consolidation (but not reconsolidation) whereas the transcription factor and immediate early gene Zif268 is required for reconsolidation but not consolidation. Memory re-consolidation occurs upon review or repetition of the learned material.

See also

The role of the amygdala in memory

• Evidence that learning-related neuronal activity in the cerebral cortex rises more slowly than in the basal ganglia, suggesting the basal ganglia may "train" this segment of cortex.

Key texts

Books

• Gold, P. E. and Greenough, W. T.(2001) (eds.), Memory Consolidation: Essays in Honor of James L. McGaugh, American Psychological Association, Washington, DC.
• McGaugh, J. L., and Herz, M. J.(1972). Memory Consolidation, Albion Publishing Company, San Francisco.

Papers

• Bloch, V., Hennevin, E., and LeConte, P. (1977) Interaction between posttrial reticular stimulation and subsequent paradoxical sleep in memory consolidation processes , in Drucker-Colin, R. R. and McGaugh, J. L. (eds.), Neurobiology of Sleep and Memory, Academic Press.
• Brown, A. S. (2002). Consolidation theory and retrograde amnesia in humans , Psychonomic Bulletin and Review 9, 403-25.
• Debiec J, LeDoux JE, Nader K. Cellular and Systems Reconsolidation in the Hippocampus. Neuron. 2002 Oct 24;36(3):527-38. PMID 12408854
• Haist, F., Gore, J. B., and Mao, H. (2001). Consolidation of human memory over decades revealed by functional magnetic resonance imaging , Nature Neuroscience 4, 1139-45
• Lee J.L, Everitt BJ, Thomas KL. Independent Cellular Processes for Hippocampal Memory Consolidation and Reconsolidation". Science. Science. 2004 May 7;304(5672):839-43. PMID 15073322

• D. Marr. Simple memory: a theory for archicortex. Philos Trans R Soc Lond B Biol Sci. 1971 Jul 1;262(841):23-81. PMID 4399412
• McGaugh, J. L. (2000). Memory: a century of consolidation , Science 287, 248-51
• Pasupathy A, Miller EK. Different time courses of learning-related activity in the prefrontal cortex and striatum. Nature. 2005 Feb 24;433(7028):873-6. PMID 15729344.
• Rose, S. P. R. (2001) Time-dependent processes in memory formation revisited , in Gold, P. E. and Greenough, W. T. (eds.), Memory Consolidation: Essays in Honor of James L. McGaugh, American Psychological Association, Washington, DC.
• Shadmehr, R. and Holcomb, H. H. (1997). Neural correlates of motor memory consolidation , Science 277, 821-

Additional material

Papers

• Galvan, V. V. and Weinberger, N. M. (2002). Long-term consolidation and retention of learning-induced tuning plasticity in the auditory cortex of the guinea pig , Neurobiology of Learning and Memory 77, 78-108.

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