Article Text
Abstract
Abstract: The problem of memory consolidation has a long scientific history, dating to end of the 19th century, yet is still a matter of vigorous research and heated debate. I will review this history briefly and then deal mainly with current developments. One aspect of the problem concerns the interaction of the neocortex with the hippocampus and related structures in the medial temporal lobes in the formation, retention and retrieval of memory with conscious awareness (also termed explicit or declarative memory). The standard consolidation model, which has many adherents, posits that the hippocampus and related structures act as temporary memory systems, needed only until memories, with their help, are consolidated in neocortex and other regions of the brain. I will present evidence that challenges this view. Contrary to the standard model, our evidence, from humans and rodents, shows the retention and retrieval of episodic memories (detailed, context-dependent autobiographical memories) depend on the hippocampus and related structures for as long as they remain episodic, no matter how long ago they were formed. Some episodic memories, however, are transformed over time and lose the detailed contextual representations that make them episodic and hippocampally dependent; they become more gist-like, semantic (memories related to general knowledge about oneself and the world) or schematic. Once transformed, the latter memories can be retained and retrieved without the hippocampus and its related structures. In short, the change in representation from the hippocampus to neocortex over time is dependent on a process of transformation rather than consolidation. A unified account is presented based on this transformation hypothesis and multiple-trace theory from which it is derived, along with implications for understanding other functions, such as imagination, planning and problem solving.