Mechanisms of Memory Consolidation and Transformation

Memory consolidation is a dynamic process occurring over the lifetime of a memory, yet the underlying mechanisms are not well understood. The hippocampus is considered to be a critical structure for the acquisition, initial storage, and retrieval of a memory, but there is considerable debate over the continuing role of the hippocampus in representing a memory as it ages. Studies in rodents and humans both point towards a reorganization of hippocampus-dependent memory traces in the cortex over time, but when and how long it takes these large-scale network changes to occur is uncertain. In this chapter, we address how a memory that is initially dependent on the hippocampus becomes represented in the cortex, independently of the hippocampus. We also discuss how the quality of the memory changes (transforms) as the trace reorganizes over time, with a focus on hippocampal-cortical interactions as described by Trace Transformation Theory (TTT), and consider the degree to which evidence related to the mechanistic basis of memory consolidation in rodents applies to complex human memory. We conclude that theories like TTT provide a new approach to thinking about consolidation as an ongoing and interactive process involving the hippocampus, mPFC, and other brain regions.