The memory for time and space differentially engages the proximal and distal parts of the hippocampal subfields CA1 and CA3.

A well-accepted model of episodic memory involves the processing of spatial and non-spatial information by segregated pathways and their association within the hippocampus. However, these pathways project to distinct proximodistal levels of the hippocampus. Moreover, spatial and non-spatial subnetworks segregated along this axis have been recently described using memory tasks with either a spatial or a non-spatial salient dimension.

Processing of spatial and non-spatial information reveals functional homogeneity along the dorso-ventral axis of CA3, but not CA1.

The ventral hippocampus is thought to principally contribute to emotional memory, while its dorsal part would be more involved in spatial processes. However, few studies have investigated ventral hippocampal function in spatial or non-spatial memories devoid of strong emotional components, and conflicting results have emerged regarding the role of the dorsal hippocampus in non-spatial (object) recognition memory. Moreover, even fewer reports have dissociated the contribution of the hippocampal subfields CA1 and CA3 to those processes, despite growing evidence of a functional segregation between these subfields.

Spatial and stimulus-type tuning in the LEC, MEC, POR, PrC, CA1, and CA3 during spontaneous item recognition memory.

According to the "two streams" hypothesis, the lateral entorhinal (LEC) and the perirhinal (PrC) cortices process information related to items (a "what" stream), the postrhinal (POR) and the medial entorhinal cortices (MEC) process spatial information (a "where" stream), and both types of information are integrated in the hippocampus (HIP). However, within the framework of memory function, only the HIP is reliably shown to preferentially process spatial information, and the PrC items' features. In contrast, the role of the LEC and MEC in memory is virtually unexplored, and conflicting results emerge for the POR.

Mapping memory function in the medial temporal lobe with the immediate-early gene Arc.

For the past two decades an increasing number of studies have underlined the crucial role of the immediate - early gene Arc in plasticity processes thought to sustain memory function. Because of the high spatial and temporal resolution of this technique, the detection of Arc products appears to have become a new standard for the mapping of cognitive processes. To date, most Arc studies have focused on identifying the contribution of the hippocampal subfields CA1 and CA3 to spatial processes.

NMDA signaling in CA1 mediates selectively the spatial component of episodic memory.

Recent studies focusing on the memory for temporal order have reported that CA1 plays a critical role in the memory for the sequences of events, in addition to its well-described role in spatial navigation. In contrast, CA3 was found to principally contribute to the memory for the association of items with spatial or contextual information in tasks focusing on spatial memory. Other studies have shown that NMDA signaling in the hippocampus is critical to memory performance in studies that have investigated spatial and temporal order memory independently.

The caudal medial entorhinal cortex: a selective role in recollection-based recognition memory.

Recent studies have suggested that the caudal medial entorhinal cortex (cMEC) is specialized for path integration and spatial navigation. However, cMEC is part of a brain system that supports episodic memory for both spatial and nonspatial events, and so may play a role in memory function that goes beyond navigation. Here, we used receiver operating characteristic analysis to investigate the role of the cMEC in familiarity and recollection processes that underlie nonspatial recognition memory in rats.

Recognition memory: adding a response deadline eliminates recollection but spares familiarity.

A current controversy in memory research concerns whether recognition is supported by distinct processes of familiarity and recollection, or instead by a single process wherein familiarity and recollection reflect weak and strong memories, respectively. Recent studies using receiver operating characteristic (ROC) analyses in an animal model have shown that manipulations of the memory demands can eliminate the contribution of familiarity while sparing recollection. Here it is shown that a different manipulation, specifically the addition of a response deadline in recognition testing, results in the opposite performance pattern, eliminating the contribution of recollection while sparing that of familiarity.