Excitotoxic lesions of the pre- and parasubiculum disrupt object recognition and spatial memory processes.

Rats with bilateral ibotenic acid lesions centered on the pre- and parasubiculum and control rats were tested in a series of spatial memory and object recognition memory tasks. Lesioned rats were severely impaired relative to controls in both the reference and working memory versions of the water maze task and displayed a delay-dependent deficit in a delayed nonmatch to place procedure conducted in the T-maze. Lesioned rats also displayed reduced exploration in a novel environment, and performance was altered in an object recognition procedure as compared with the control group. These findings indicate that the pre- and parasubiculum plays an important role in the processing of both object recognition and spatial memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel involvement of perirhinal and lateral entorhinal cortex in the polysynaptic activation of hippocampus by olfactory inputs

BACKGROUND AND AIMS OF THE STUDY: There is a need for a replacement cardiac valve constructed from non-immunogenic materials but incorporating living, and preferably autologous, cells. The object of this study was to colonize freeze-dried porcine valve leaflets with human fibroblasts and vascular endothelial cells. METHODS: Porcine pulmonary valve leaflets were freeze-dried to produce a porous matrix having communicating cavities of appropriate dimensions for fibroblast repopulation. Cultured human fibroblasts and vascular endothelial cells that had been cryopreserved by standard methods were added to freeze-dried leaflets. Following culture at 37 degrees C, the leaflets were examined by confocal scanning microscopy and transmission electron microscopy. RESULTS: Mechanical perforation of the leaflet surface permitted colonization of the freeze-dried matrix by fibroblasts; under the conditions we studied, the cell density did not reach physiologic levels but those cells that were present were well attached and metabolically active. Gentle cotton abrasion of the surface of the freeze-dried leaflets provided a suitable substrate for endothelial cell attachment and confluence was achieved in 10 days. Leaflets were perforated, cultured with human fibroblasts for 10 days, then gently rubbed with a cotton bud and cultured for a further 10 days with human endothelial cells. The endothelial cells formed a confluent layer on the surface and viable fibroblasts were present within the substance of the leaflet. CONCLUSION: Although these results are preliminary, they demonstrate the basic feasibility of this approach to the production of xenogeneic valves that contain the patient's own cells.     

The effects of NMDA lesions centered on the postrhinal cortex on spatial memory tasks in the rat.

Rats with bilateral N-methyl-D-aspartate lesions centered on the postrhinal cortex (POR) and sham lesions were tested in a series of spatial memory tasks. The POR-lesioned rats were significantly impaired compared with sham rats in the reference memory version of both the water maze and radial arm maze tasks and in the standard radial arm maze working memory task. The POR-lesioned rats displayed a delay-independent impairment in the working memory versions of the water maze and in a delayed nonmatching-to-place (DNMP) version of the radial arm maze task. The POR-lesioned rats were also impaired in a DNMP procedure conducted in the T-maze. These findings indicate that the POR has a delay-independent role in the processing of spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of excitotoxic lesions centered on the perirhinal cortex in two versions of the radial arm maze task.

Rats with bilateral ibotenic acid lesions centered on the perirhinal cortex and sham-operated controls were tested in 2 versions of a spatially guided radial arm maze task. Lesioned rats made significantly more errors and required more sessions to reach criterion relative to controls in the standard radial maze task. When they were tested in a delayed nonmatch to sample version of this task, lesioned rats made more errors during the predelay phase and at both the 30-s and 10-min delays of the postdelay phase. These findings provide further support for the hypothesis that the role of the perirhinal cortex in object recognition memory may include reference to some spatial aspect of the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Excitotoxic lesions centered on perirhinal cortex produce delay-dependent deficits in a test of spatial memory

The purpose of the study was to assess developments in the theory of mind suggested by changes in the organization of cognitive verb extensions during the elementary school years. Adults and 3rd- and 5th-grade children were provided with a set of mental activity scenarios and were asked to select the best verbs from a list of cognitive verbs that might apply to each scenario. Changes in organization were assessed by examining overlapping uses of cognitive verbs in different contexts. There were 3 major changes with development: (a) the understanding of the role of memory in input functions increased, (b) the interrelatedness of memory- and comprehension-related verbs increased, and (c) the importance of cognitive certainty and uncertainty engaged by constructive processing verbs increased. Together, these findings suggest that a constructivist theory of mind develops in later childhood.     

The dynamic nature of spatial encoding in the hippocampus.

Many hippocampal neurons (place cells) appear to represent a particular location within an environment (their place field). This property would appear to be central to hippocampal involvement in navigation based on spatial memory. Although a navigationally useful representation might also include information about distal goals, having a place field and being able to represent a distal goal would appear to be mutually exclusive place cell properties. Our simulations demonstrate, however, that information about goal direction can be simply derived from the changes in place field density that occur when place fields shift location in a goal-directed manner. Previous reports that place fields respond dynamically to shifts in goal location may, therefore, represent the operation of such a system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of excitotoxic lesions centered on the hippocampus or perirhinal cortex in object recognition and spatial memory tasks.

Rats with bilateral ibotenic acid lesions centered on the hippocampus (HPC) or perirhinal cortex (PRC) and sham-operated controls were tested in a series of object recognition and spatial memory tasks. Both HPC and PRC rats displayed reduced habituation in a novel environment and were impaired in an object-location task. HPC rats were severely impaired in both the reference and working-memory versions of the water maze and radial arm maze tasks. In contrast, although PRC rats displayed mild deficits in the reference memory version of the water maze and radial arm maze tasks, they were markedly impaired in the working-memory version of both the tasks. These findings demonstrate that under certain conditions both the HPC and PRC play a role in the processing of spatial memory. Further investigation of these conditions will provide important new insights into the role of these structures in memory processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perirhinal cortex contributions to performance in the Morris Water Maze.

Rats with bilateral, electrolytic lesions of perirhinal cortex (PRC), lateral entorhinal cortex (LEC), or combined lesions (PRLE) were impaired relative to controls (sham) during initial acquisition in the Morris water maze, although all groups were eventually able to learn to locate the platform. A further deficit in the performance of PRC and PRLE, but not LEC groups, was evident, however, when a probe trial was conducted 2 min (but not 24 hours) after training. When the performance of sham- and PRC-lesioned rats was tested with variable memory delays inserted between training and probe trials, lesioned rats displayed an increase in the rate of forgetting for information made available during the training trial. This finding suggests that the PRC normally stores information regarding the cue–platform relationship and transfers this information to related structures during water maze performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of cytotoxic perirhinal cortex lesions on spatial learning by rats: A comparison of the dark Agouti and Sprague-Dawley strains.

The effects of perirhinal cortex lesions in rats on spatial memory might depend on the choice of strain. The present study, therefore, compared perirhinal lesions in Sprague-Dawley rats (associated with deficits) with Dark Agouti rats (associated with null effects). Tests of reference memory and working memory in the water maze failed to provide evidence that perirhinal lesions disrupt overall levels of performance (irrespective of strain) or that these lesions have differential effects on the rates of spatial learning in these 2 strains. Strain differences were, however, found, as the Dark Agouti strain was often superior. Furthermore, the perirhinal lesions did have differential effects in the 2 strains, but these did not appear to relate directly to changes in spatial learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of rat perirhinal cortex exacerbate the memory deficit observed following damage to the fimbria-fornix.

Rats that had received bilateral lesions of the perirhinal cortex, fimbria-fornix, combined lesions of both these structures, or sham operations were tested on an object-guided delayed non-match-to-sample task. Perirhinal lesioned and fimbria-fornix lesioned rats were moderately impaired when delay intervals of 30 s or more were introduced between the sample and test phases of the experiment. Animals with combined lesions displayed a considerably greater impairment than animals with lesions of either structure alone. The combined lesioned animals were severely impaired in the initial acquisition of the task and displayed a profound memory deficit at delay intervals of greater than 4 s. These results emphasize the importance of the perirhinal cortex to memory function and suggest that the perirhinal cortex and the hippocampal formation may function interactively in the execution of memory processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)