Systems consolidation and hippocampus: two views

Two approaches to systems-level memory consolidation are contrasted. The standard model and multiple trace theory are spelled out, their implications are outlined, and their fit to the data from a number of approaches is evaluated. We conclude that the data from neuroimaging studies strongly support multiple trace theory, that data from neuropsychological studies favor but does not conclusively support multiple trace theory, while evidence from a new approach, the study of prospective memory, also supporting multiple trace theory, offers a promising new way to distinguish between these two theories. Work with animals is largely consistent with this conclusion. We suggest that the hippocampal and neocortical systems are critical for different forms of memory, and that the shift of memory from dependence on hippocampus to dependence on neocortex during consolidation is a reflection of the fact that memory often is transformed with time, becoming more generic in nature. Insofar as detailed episodic recollections are retained, the data show that they are dependent on the hippocampal system, much as multiple trace theory postulated.