Dissociating the role of the parietal cortex and dorsal hippocampus for spatial information processing.

Dorsal hippocampus, parietal cortex, and control lesioned rats were tested on both a metric and topological task. The metric task consisted of 2 different objects placed 68 cm apart on a cheese board. After habituation, the objects were moved to a separation of 38 cm on Day 1 and to a separation of 98 cm on Day 2. The topological task consisted of 4 different objects placed in a square orientation. After habituation, the first 2 objects were switched, and after the rats habituated to that change, the back 2 objects were switched. This was repeated on a different day with 4 new objects. The data suggest that the hippocampus is necessary for metric representations, whereas the parietal cortex is necessary for topological representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociating the roles of dorsal and ventral CA1 for the temporal processing of spatial locations, visual objects, and odors.

The differential contributions of the dorsal and ventral hippocampus for learning and memory have long been of interest. The present experiments were designed to evaluate the contributions of dorsal CA1 and ventral CA1 for temporal processing. Animals were run on three temporal ordering paradigms: one with visual objects, one with olfactory stimuli, and one with spatial locations. Animals with lesions to dorsal CA1 showed deficits for the temporal ordering of visual objects relative to control animals, and deficits for the temporal ordering of spatial locations relative to control and ventral CA1 lesioned animals. Animals with lesions to ventral CA1 showed deficits for the temporal ordering of olfactory information relative to control and dorsal CA1 lesioned animals, and a mild deficit for the temporal ordering of visual objects relative to control animals, but not as severe as those shown by the dorsal CA1 lesioned animals. These data suggest that dorsal CA1 and ventral CA1 contribute to temporal ordering processes, and that dorsal CA1 and ventral CA1 are dissociable for temporal ordering based upon the nature of the information that is processed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Double dissociation of function within the hippocampus: Spatial memory and hyponeophagia.

Complete and dorsal hippocampal lesions impaired spatial performance on 2 working memory tasks: rewarded alternation on the T maze and matching to position in the water maze. In contrast, ventral hippocampal lesions had no effect on these tasks, even when task difficulty was increased by the introduction of delays. Ventral lesions did resemble complete lesions in reducing anxiety in 3 commonly used tests of anxiety (social interaction, plus-maze, and hyponeophagia). Dorsal lesions also appeared to be anxiolytic in the social interaction and plus-maze tests, but they did not affect hyponeophagia. Complete- and dorsal-lesioned rats displayed hyperactivity, whereas ventral-lesioned rats did not. These results show a double dissociation between dorsal and ventral hippocampal lesions (hyponeophagia vs. spatial memory), suggesting differentiation of function along the septotemporal axis of this structure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociations of the medial and lateral perforant path projections into dorsal DG, CA3, and CA1 for spatial and nonspatial (visual object) information processing.

Medial perforant path plasticity can be attenuated by 2-amino-5-phosphonovaleric acid (APV) infusions, whereas lateral perforant path plasticity can be attenuated by naloxone infusions. The present experiment was designed to evaluate the role of each entorhinal efferent pathway into the dorsal hippocampus for detection of spatial and nonspatial (visual object) changes in the overall configuration of environmental stimuli. Dorsal dentate gyrus infusions of either APV or naloxone attenuated detection of a spatial change, whereas only naloxone infusions disrupted novel object detection. Either APV or naloxone infusions into dorsal CA3 disrupted both spatial and novel object detection. APV infusions into dorsal CA1 attenuated detection of a spatial change, whereas naloxone infusions into dorsal CA1 disrupted novel object detection. These data suggest that each dorsal hippocampal subregion processes spatial and nonspatial (visual object) information from perforant path efferents in a unique manner that is consistent with the intrinsic properties of each subregion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of CA3 and CA1 in the acquisition of an object-trace-place paired-associate task.

The hippocampus mediates associative learning involving spatial and temporal information. Specifically, paired associations in which a trace interval separates the elements appear to be associated within CA1. In contrast, CA3 appears to be involved in associations containing spatial elements. This suggests that CA3, but not CA1, is involved as long as the spatial association does not contain temporal elements; conversely, CA1 is involved when a temporal element is included, regardless of whether there are spatial elements present. In the present study, rats were run on an object-trace-place paired-associate learning paradigm. Rats with CA3 as well as rats with CA1 lesions showed deficits in the acquisition of this task. These results suggest that CA1 is involved in making arbitrary associations involving a temporal (trace) element, whereas CA3 is involved in making associations that involve spatial elements; furthermore, CA1 and CA3 interact in the presence of both spatial and temporal information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial cognitive maps in animals: New hypotheses on their structure and neural mechanisms.

Provides a hierarchical model of animal spatial cognitive maps. Such maps include both topological information, which affords loose, yet operational, representations of the connectivity of space and its overall arrangement, and metric information, which provides information about angles and distances. The model holds that maps can be initially described as a set of location-dependent reference frameworks providing directional information about other locations. The addition of an overall directional reference allows for the buildup of more complete (allocentric) representations. A survey of recent neurobiological data provides some hints about the brain structures involved in these processes and suggests that the hippocampal formation and the posterior parietal cortex would act differently by handling topological and metric information, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The "Swedish" mutation of the amyloid precursor protein (APPswe) dissociates components of object-location memory in aged Tg2576 mice.

Aged Tg2576 mice show abnormalities in hippocampal morphology and physiology and display behavioral deficits in spatial navigation tasks consonant with a deficit in the functional properties of the hippocampus. However, the nature of the spatial representations disrupted by the "Swedish" mutation of the amyloid precursor protein (APPswe) is unclear. In an effort to characterize the memory deficits in Tg2576 mice, the spontaneous object exploration paradigm was used to interrogate spatial and object memory in mice. With object arrays of comparable size, 16-month-old Tg2576 mice showed a normal object familiarity/novelty effect but impaired memory for the location of objects when 2 objects exchanged locations (topological transformation; Experiment 1). In contrast, Tg2576 mice showed preferential exploration of familiar objects when they were moved to previously unoccupied locations (Experiment 2), irrespective of whether the transformation altered the metric properties of the object array (Experiments 3). These results suggest that Tg2576 mice are able to form representations of the identity of objects and a memory of the spatial organization of objects in an arena. In contrast, conjunctive memory for specific object-location associations is severely impaired in aged Tg2576 mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential roles of dorsal hippocampal subregions in spatial working memory with short versus intermediate delay.

In order to determine the role of subregions of the hippocampus in spatial working memory, this study combined selective neurotoxic lesions of the hippocampal subregions with a simple delayed nonmatching-to-place task on a radial maze in rats. Lesions of the dentate gyrus or the CA3, but not the CA1, subregion of the hippocampus induced a deficit in the acquisition of the task with short-term delays (i.e., 10 sec) and impaired performance of the task in a novel environment. All subregional lesions produced sustained impairment in performing the task with intermediate-term delays (i.e., 5 min) when rats were tested in a familiar environment. The results suggest a dynamic interaction among the dorsal hippocampal subregions in processing spatial working memory, with the time window (i.e., delay) of a task recognized as an essential controlling factor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A behavioral analysis of the role of CA3 and CA1 subcortical efferents during classical fear conditioning.

It has been proposed that the hippocampus and subcortical structures interact during the processing of fear and anxiety-related information. It has been demonstrated that the subcortical efferents from CA3 and CA1 can be selectively disrupted without concomitant disruption to the afferents. The present experiment was designed to evaluate the role of CA3 efferents via the fimbria and the CA1 efferents via the dorsal fornix for encoding and consolidation/retrieval of classical fear conditioning. The present data suggest that the subcortical projections from CA3 and CA1 are differentially involved in the processing of classical fear conditioning, with CA3 subcortical efferents supporting acquisition of both cued and contextual fear but only supporting retention of contextual fear and CA1 subcortical efferents supporting the encoding and retrieval of both cued and contextual fear. These data further suggest that all hippocampal efferents are not homogeneous, and that the hippocampus and subcortex interact to process conditioned fear. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dorsal hippocampus, CA3, and CA1 lesions disrupt temporal sequence completion.

An experiment was designed to evaluate effects of dorsal hippocampus, dorsal CA3a,b, dorsal CA1, and control lesions on performance of a temporal sequence task. Rats were trained on a sequential learning task involving six spatial locations on a radial 8-arm maze. After initial training followed by surgery, it was found that all lesioned animals were able to remember the sequence. To test temporal sequence completion, rats were started at different positions in the sequence and expected to complete the remainder of the sequence. The results indicate that control rats had no difficulty completing the sequence, regardless of starting point. In contrast, rats with dorsal hippocampus and dorsal CA3a,b lesions made errors by always returning to the first position in the sequence, regardless of which start position was used, whereas rats with dorsal CA1 lesions made random errors in the process of completing the sequence and did not appear to remember the serial order of the spatial sequence. This suggests that the dorsal hippocampus, and specifically the dorsal CA3 in conjunction with CA1, may be involved in temporal pattern completion processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial working memory is independent of hippocampal CA1 long-term potentiation in rats.

This study investigated the relationship between spatial working memory and hippocampal long-term potentiation (LTP) using the allocentric place discrimination task (APDT) in rats, in which the selection accuracy is a good index for spatial working memory. Either the selective M1 muscarinic receptor antagonist pirenzepine (50 μg) or the choline uptake inhibitor hemicholinium-3 (5 μg) impaired APDT selection accuracy, but neither affected the induction of LTP in the hippocampal CA1 region in anesthetized rats. In contrast, the selective N-methyl-{d}-aspartate receptor antagonist D-amino-5-phosphonopentanoate (200 nmol) did not impair APDT selection accuracy but completely blocked hippocampal CA1 LTP. These results suggest that spatial working memory is independent of hippocampal CA1 LTP and that the central cholinergic system is involved in spatial working memory, but not through the modulation of hippocampal CA1 LTP. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brain aging: changes in the nature of information coding by the hippocampus

Advanced age in rats is associated with a decline in spatial memory capacities dependent on hippocampal processing. As yet, however, little is known about the nature of age-related alterations in the information encoded by the hippocampus. Young rats and aged rats identified as intact or impaired in spatial learning capacity were trained on a radial arm maze task, and then multiple parameters of the environmental cues were manipulated to characterize the changes in firing patterns of hippocampal neurons corresponding to the presence of particular cues or the spatial relationships among them. The scope of information encoded by the hippocampus was reduced in memory-impaired aged subjects, even though the number of neurons responsive to salient environmental cues was not different from that in young rats. Furthermore, after repeated manipulations of the cues, memory-intact aged rats, like young rats, altered their spatial representations, whereas memory-impaired aged rats showed reduced plasticity of their representation throughout testing. Thus changes in hippocampal memory representation associated with aging and memory loss can be characterized as a rigid encoding of only part of the available information.     

"Differential involvement of the dorsal anterior cingulate and prelimbic-infralimbic areas of the rodent prefrontal cortex in spatial working memory": Correction to Ragozzino et al. (1998).

Reports an error in "Differential involvement of the dorsal anterior cingulate and prelimbic-infralimbic areas of the rodent prefrontal cortex in spatial working memory" by Michael E. Ragozzino, Spencer Adams and Raymond P. Kesner (Behavioral Neuroscience, 1998[Apr], Vol 112[2], 293-303). Figure 1 (page 295) and Figure 4 (page 299) were printed incorrectly. The corrected figure pages and corresponding captions are provided in the erratum. (The following abstract of the original article appeared in record 1998-01023-003.) The present study examined the effects of quinolinic acid lesions of the dorsal anterior cingulate and prelimbic-infralimbic cortices on spatial working memory and spatial discrimination using go/no-go procedures. All testing occurred in a 12-arm radial maze. In a working memory task, rats were allowed to enter 12 arms for a cereal reward. Three or 4 arms were presented for a 2nd time in a session, which did not result in a reward. In a spatial discrimination task, rats had successive access to 2 different arms. One arm always contained a reward, and the other never contained a reward. Prelimbic-infralimbic lesions impaired spatial working memory but only produced a transient spatial discrimination deficit. Dorsal anterior cingulate lesions did not induce a deficit in either task. These findings suggest that the prelimbic-infralimbic cortices, but not the anterior cingulate cortex, are important in spatial working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Role of Hippocampal Regions CA3 and CA1 in Matching Entorhinal Input With Retrieval of Associations Between Objects and Context: Theoretical Comment on Lee et al. (2005).

Models of hippocampal function have proposed different functions for hippocampal regions CA3 and CA1, commonly proposing that CA1 performs a match-mismatch comparison of memory retrieval with sensory input. The study by I. Lee, M. R. Hunsaker, and R. P. Kesner (2005) tested these models using selective lesions of hippocampal subregions (see record 2005-01705-014). Their data suggest that CA3 and the dentate gyrus play an important role in the process of detecting the mismatch when a familiar object is placed in a new spatial location. Lesions of the dentate gyrus and CA3 strongly reduce the enhanced exploration associated with displaced objects, beyond the reduction caused by CA1 lesions. This supports the importance of convergent input to CA3 as well as CA1. Along with recent electrophysiological data, this provides a framework for more specifically modeling the role of CA3 and CA1 in matching sensory input with context-dependent retrieval for memory-guided behavior in different tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Altered spatial learning and memory in mice lacking the mGluR4 subtype of metabotropic glutamate receptor.

The glutamate analog, L-2-amino-4-phosphonobutyric acid (L-AP4) is a selective agonist for several members of the metabotropic glutamate receptor (mGluR) family. Activation of presynaptic mGluRs by L-AP4 causes a suppression of synaptic transmission in the central nervous system. In this study, the role of 1 subtype of mGluR in the nervous system was investigated by analyzing mutant mice lacking the L-AP4-sensitive receptor, mGluR4. Experiments designed to probe hippocampal function showed no impairments in acquisition of spatial learning in the water maze task. However, in a spatial reversal learning task, the mutant mice exhibited significantly accelerated learning performance. Furthermore, in a probe trial administered 6 weeks posttraining, these mice showed impaired spatial accuracy. The results suggest that the mutant mice differed in their ability to learn and integrate new spatial information into previously formed memory traces and that their use of stored spatial information also was altered. Thus, the presynaptically expressed mGluR4 plays a role in the processing of spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal and caudate metabolic activity associated with different navigational strategies.

Hippocampal and striatal systems are widely related to spatial tasks. Depending on the strategies used, different memory systems can be activated. In this study, the authors used the cytochrome c-oxidase technique as a functional marker of the hippocampal and dorsal striatum activity related to training in several water maze tasks. Current results show a differential participation of the hippocampal and striatal systems in navigation. When spatial information is relevant, participation of the hippocampal system is more important, and when the task is similar to a response learning one, the striatal system is more active. According to computational models, CA3 seems to be more active when the associative demand is higher, whereas CA1 and dentate gyrus activity are higher when spatial information processing is required. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Redistribution of spatial representation in the hippocampus of aged rats performing a spatial memory task.

Young and old rats performed on a maze according to a forced-choice and then a spatial memory procedure either in the same or a different environment. Aged rats were slower to learn the spatial memory task when tested in the same, but not in a different, room. One interpretation of this pattern of results is that although old rats learn new rules as quickly as young rats, they show less flexibility with old rules and familiar spatial information. Impaired choice accuracy during asymptote performance suggests poor processing of trial-unique information by old rats. Spatial correlates of hippocampal CA1 and hilar cells varied with task demand: CA1 cells of aged rats showed more spatially selective place fields, whereas hilar cells showed more diffuse location coding during spatial memory, and not forced-choice, tests. Such representational reorganization may reflect a compensatory response to age-related neurobiological changes in the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pharmacological evidence of the role of dorsal striatum in spatial memory consolidation in mice.

This study investigated the role of dorsal striatum in spatial memory in mice. The mice were tested for their ability to detect a spatial displacement 24 hrs after training. In order to manipulate the dorsal striatum, focal administrations of the N-methyl-D-aspartate (NMDA) antagonist D-2-amino-5 phosphonopentanoic acid (AP-5) were performed immediately after training. AP-5 impaired the mice's ability to detect the spatial change only if their initial position was constant during training and testing. These findings demonstrate that NMDA receptor blockade within the dorsal striatum impairs spatial memory consolidation in a task in which no explicit reward or procedural learning is involved. The results are discussed with reference to a possible selective involvement of this structure in processing spatial information acquired through an egocentric, but not an allocentric, frame of reference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preserved Spatial Memory Over Brief Intervals in Older Adults.

Two studies compared young and older adults' memory for location information after brief intervals. Experiment 1 found that accuracy of intentional spatial memory for individual locations was similar in young and older participants for set sizes of 3 and 6. Both groups also encoded individual locations in relation to the larger configuration of locations. Experiment 2 showed that like young adults, older adults' latency to respond to a test probe in a letter working memory task was negatively influenced by spatial information that was irrelevant to the task. This interference effect indicated preserved incidental memory for spatial information in older adults. Together, these data suggest that initial encoding of spatial information for relatively small numbers of items is largely preserved in healthy older adults and that representations of spatial information persist over short intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory: A Rosetta stone for rat and human hippocampal discourse: Theoretical comment on Goodrich-Hunsaker and Hopkins (2010).

The article by Goodrich-Hunsaker and Hopkins (2010, this issue) takes up an important place among in the recent contributions on the role of the hippocampus in memory. They evaluate the effect of bilateral damage to the hippocampus on performance by human participants in a virtual 8-arm radial maze. The hippocampal damage appears to be highly selective and nearly complete. Exactly as with selective hippocampal damage in rats, the human participants showed a deficit in accurately choosing rewarded versus never-rewarded arms and a deficit in avoiding reentering recently visited arms. The results are triply significant: (1) They provide good support for the idea that the wealth of neurobiological information, from network to synapse to gene, on spatial memory in the rat may apply as a whole to the human hippocampal memory system; (2) They affirm the utility of human virtual task models of rat spatial memory tasks; (3) They support one interpretation of the dampening of the hippocampal functional MRI (fMRI) blood oxygen level-dependent (BOLD) signal during performance of the virtual radial arm maze observed by Astur et al. (2005). (PsycINFO Database Record (c) 2010 APA, all rights reserved)