Hippocampus, space, and memory

Abstract

We examine two different descriptions of the behavioral functions of the hippocampal system. One emphasizes spatially organized behaviors, especially those using cognitive maps. The other emphasizes memory, particularly working memory, a short-term memory that requires iexible stimulus-response associations and is highly susceptible to interference. The predictive value of the spatial and memory descriptions were evaluated by testing rats with damage to the hippocampal system in a series of experiments, independently manipulating the spatial and memory characteristics of a behavioral task. No dissociations were found when the spatial characteristics of the stimuli to be remembered were changed; lesions produced a similar deficit in both spatial and nonspatial test procedures, indicating that the hippocampus was similarly involved regardless of the spatial nature of the task. In contrast, a marked dissociation was found when the memory requirements were altered. Rats with lesions were able to perform accurately in tasks that could be solved exclusively on the basis of reference memory. They performed at chance levels and showed no signs of recovery even with extensive postoperative training in tasks that required working memory. In one experiment all the characteristics of the reference memory and working memory procedures were identical except the type of memory required. Consequently, the behavioral dissociation cannot be explained by differences in attention, motivation, response inhibition, or the type of stimuli to be remembered. As a result of these experiments we propose that the hippocampus is selectively involved in behaviors that require working memory, irrespective of the type of material (spatial or nonspatial) that is to be processed by that memory.

A Role of Fos Expression in the CA3 Region of the Hippocampus in Spatial Memory Formation in Rats

“…These results are consistent with the well-established role of these brain areas in learning and memory (Olton et al 1979;Morris et al 1982;Kesner et al 1987;Jarrard 1993;Rudy and Sutherland 1995). Some studies have shown that the dorsal hippocampal formation is more important than the ventral formation for spatial learning (Jung et al 1994;Moser et al 1995).…”

“…The training trial continued until all four baits in the food cups had been consumed or until 5 min had elapsed. Reference memory is regarded as a long-term memory for information that remains constant over repeated trials (memory for the positions of baited arms), whereas working memory is considered a short-term memory in which the information to be remembered changes in every trial (memory for the positions of arms that had already been visited in each trial; Olton et al 1979). Thus, measures were made of the number of reference memory errors (entering an arm that was not baited) and working memory errors (entering an arm containing food but previously entered).…”

Spatial Memory Deficits Induced by Perinatal Treatment of Rats with PCP and Reversal Effect of D-Serine

“…Consequently, we initially investigated the effect of PCP administration in perinatal rats on their performance in three different Morris (1984) water maze tasks in adulthood. Firstly, animals were tested on a reference spatial memory task in order to investigate their long-term spatial memory, and secondly on a reference reversal memory task in order to test their ability to inhibit a long-term acquisition, and finally on a spatial working memory task (Aggleton et al, 1986;Pouzet et al, 1999Pouzet et al, , 2002 in order to test the ability of rats to inhibit short-term memory acquisition (Eichenbaum and Cohen, 2001;Olton et al, 1979). Female rats have being previously described as sensitive to this PCP treatment (Wang et al, 2001), so we tested both males and females.…”

Effects of hippocampal damage on reward threshold and response rate during self-stimulation of the ventral tegmental area in the rat

“…Although traditionally implicated in processes such as spatial memory [40,41], working memory [38], and response inhibition [1,18], accumulating evidence indicates that the hippocampal formation exerts an important modulatory influence over behaviors directly mediated by the nucleus accumbens (NACC). This modulatory influence has been consistently demonstrated in many studies of spontaneous and drug-induced locomotion.…”