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Detailed memories for unique episodes from an individual's past can be triggered, often effortlessly, when that individual is exposed to a stimulus that was present during the original event. The aim of Kesner et al. (2008) is to understand the neural basis of memory encoding that supports this cued recall of episodic memories. Kesner and colleagues make novel use of an object-place paired-associate task for rats to provide evidence for a critical role of dorsal CA3 in certain aspects of episodic memory encoding. Using one-trial cued recall versions of the task they show that when rats are cued with an object stimulus, they can be trained to revisit the location in which the object appeared previously. Conversely, when rats are cued with a location, they can learn to choose the object with which it was associated. Rats with dorsal CA3 lesions are severely impaired at these tasks. These data are consistent with the theory that the autoassociative network in CA3 supports the rapid formation of novel associations and may allow pattern completion―the phenomenon whereby a subset of the cues present at an encoding event triggers recall of the whole event. Although flexible recall of arbitrary associations is not fully demonstrated, the study contributes 2 novel behavioral tasks to the previously limited repertoire for studying paired associate recall in rats. It also builds on previous data to specify the role of the hippocampal CA3 subregion in cued recall―a critical aspect of episodic memory. [ABSTRACT FROM AUTHOR]

To examine whether the hippocampus is required for memory for unique experiences independent of their spatial or temporal context, the authors devised a novel task that requires rats to remember odor-reward associations formed within a single training trial. Unlike previous tests of l-trial memory, in this task new associations with otherwise familiar stimuli must be formed, and accurate judgments cannot be based on relative familiarity or recency of the stimuli. The authors show that intact rats performed well on this novel test of event memory. Furthermore, rats with lesions of the hippocampus showed no impairments, even over long retention intervals. These data suggest that the hippocampus is not required for event-specific stimulus-reward associations and that other brain structures mediate this aspect of episodic memory. [ABSTRACT FROM AUTHOR]

Focuses on an experiment which seeks to solve a paradox relating to injuries of the hippocampus region in rats. Explanation of paradox; Details of experiments; Effects of injuries to hippocampus region on memory; Listing of related studies; Possible damage resulting from Postischemic processes.