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 a couple of distinct processes:

• The molecular process by which long-term conductivity of synapses is affected. Memory consolidation occurs after training or a single exposition to a stimulus-response pair .
• Many researchers believe that episodic memories are initially stored in a part of the brain called the hippocampus and are slowly moved (or 'consolidated') into the neocortex. This process of consolidation may happen during sleep, perhaps during dreaming.

Reconsolidation

There is evidence 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. Maximum consolidation with minimum time investment is achieved by means of spaced repetition.

Research papers of interest

• Lee J. L., Everitt B. J., Thomas K. L. "Independent Cellular Processes for Hippocampal Memory Consolidation and Reconsolidation". Science. 2004 May 7;304(5672):839-43. Epub 2004 Apr 08

• Pasupathy A., Miller E.K. "Different time courses of learning-related activity in the prefrontal cortex and striatum" Nature. 2005 Feb 24; 433:873-876 - evidence that the cerebral cortex learns slowly... if the CC learns slowly then this would support the idea that the hippocampus acquires memories quickly and then slowly 'trains' the CC over time.