Consolidation of Episodic Memory: An Epiphenomenon of Semantic Learning
Two hypotheses dominate the literature on systems consolidation of episodic memory: the transfer hypothesis and the transformation hypothesis. The former postulates a transfer of episodic memory from a fast-learning hippocampus to a slow-learning neocortex. The latter postulates that only the hippocampus genuinely stores episodic memories, and that systems consolidation arises due to multiple memory traces in the hippocampus and a transformation of episodic into semantic memories. While both hypotheses are supported by some evidence, they are contradicted by other, and hence remain controversial. Here, I suggest a new account of systems consolidation. It is based on the transformation hypothesis and introduces two modifications. First, episodic and semantic memory differ in their representational format, which is optimized for different purposes: Rigid sequences for episodic memories and flexible representations for semantic memory. Second, multiple memory traces in the hippocampus are not required to account for the temporal gradient of retrograde amnesia, if there is any. To this end, slow semantic learning from episodic memories suffices. The main hypothesis that I propose in this chapter is that systems consolidation is an epiphenomenon of semantic learning from episodic memory.