The temporal attributes of episodic memory

From a temporal dynamic processing point of view, episodic memory can be divided into three critical time periods: short-term episodic memory with a duration of seconds, intermediate-term episodic memory with a duration from minutes to hours, and long-term or remote episodic memory with a duration from days to years. We propose that short-term episodic memory is mediated by the CA3 subregion of the hippocampus, intermediate-term episodic memory is mediated by the CA1 subregion of the hippocampus (in certain situations aided by the CA3 subregion), and that long-term or remote episodic memory may be mediated by the CA1 subregion. In support of the above mentioned proposal data are presented to support the short-term and intermediate episodic memory functions of CA3 and CA1 based on single item object, spatial location, and object-place association tasks. Additional data are presented for a role for CA3 in short-term episodic memory based on multiple sequential spatial locations, visual objects, and odors tasks. The same episodic memory model based on duration mentioned above cannot easily be applied to the functions of the CA3 (short-term episodic) and CA1 (intermediate-term episodic) for a multiple sequentially presented item, such as a places, objects or odors. The reason for this is that the CA1 region supports, in addition to intermediate episodic memory, temporal pattern separation processes which would reduce interference among sequentially experienced items. The consequence is that this temporal pattern separation process can result in CA1 involvement in short-term episodic tasks based on duration. Also, data are presented based on tasks that involved multiple-trials tested within a day and between days short-term and intermediate-term episodic memory. Furthermore, the mechanisms for understanding the interactions and dissociations between CA3 and CA1 are discussed. The DG appears to have a modulatory influence on the CA3 and CA1 mediation of short-term and intermediate-term episodic memory. The role of CA1 in supporting remote episodic memory requires more experimentation. (C) 2010 Elsevier B.V. All rights reserved.