A double dissociation between the rat hippocampus and medial caudoputamen in processing two forms of knowledge.

Rats with hippocampus, medial caudoputamen (CPU), lateral CPU, or control lesions were trained on declarative and procedural knowledge variants of a novel rodent sequential learning task. Medial CPU lesions impaired rats' ability to learn the procedure of running through a sequence of open maze arms but did not disrupt their capacity to explicitly generate (i.e., "declare") maze arm sequences. Hippocampus lesions produced the opposite set of results. Rats with lateral CPU lesions were not impaired on either version of the task. Transfer tests indicated that control rats predominantly used egocentric cues to solve the procedural task and allocentric spatial cues to solve the declarative task. These findings suggest a double dissociation between the medial CPU and hippocampus in processing egocentric-procedural and allocentric- declarative sequential information, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does pretraining spare the spatial deficit associated with anterior thalamic damage in rats?

Rats that had been pretrained on 2 tests of allocentric memory (water maze and T maze) received bilateral cytotoxic lesions in the anterior thalamic nuclei (ATN) or transection of the fimbria-fornix (FF). After surgery, both groups of rats were impaired on both tasks, although the preoperative training resulted in a rapid initial reacquisition of the water maze task. Those rats with lesions largely restricted to the ATN were impaired at a level comparable to that produced by FF lesions. This finding is consistent with a close functional relationship between the hippocampus and the ATN, necessary for the acquisition and on-line processing of allocentric spatial information but not for the maintenance/retrieval of procedural information. The rats with more extensive thalamic lesions were more impaired in both tasks and did show a loss of procedural information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perirhinal cortex and place–object conditional learning in the rat.

The present study examined whether excitotoxic lesions of the perirhinal cortex can affect acquisition of a place–object conditional task in which object and spatial information must be integrated. Testing was carried-out in a double Y-maze apparatus, in which rats learned a conditional rule of the type, "In Place X, choose Object A, not Object B (A+ vs B–); in Place Y, choose Object B, not Object A (A– vs B+)." Perirhinal cortex lesions significantly impaired acquisition of this task while sparing performance of an allocentric spatial memory task performed in a radial arm maze. Perirhinal cortex lesions also had no apparent effect on a 1-pair object discrimination task performed in the double Y-maze or on retention and acquisition of 4-pair concurrent discrimination problems performed in a computer-automated touch screen testing apparatus. The results suggest that, although the perirhinal cortex and hippocampus can be functionally dissociated, their normal mode of operation includes the integration of object and spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of dorsal versus ventral hippocampal, total hippocampal, and parietal cortex lesions on memory for allocentric distance in rats.

To test for the contribution of the parietal cortex and hippocampus to memory for allocentric spatial cues, the authors trained rats on a go/no-go task that required the rat to remember the distance between two visual cues. Total hippocampal lesions impaired working-memory representation for allocentric distance, whereas parietal cortex lesions resulted in only a transient impairment. In a second experiment, neither hippocampal nor parietal cortex lesions impaired allocentric distance discrimination. A third experiment showed that both the dorsal and ventral areas of the hippocampal formation must be destroyed to impair working memory for allocentric distance information. There appears to be a dissociation between the hippocampus and parietal cortex in mediating memory for allocentric distance information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Place cells and place navigation

The assumption that hippocampal place cells (PCs) form the neural substrate of cognitive maps can be experimentally tested by comparing the effect of experimental interventions on PC activity and place navigation. Conditions that interfere with place navigation (darkness, cholinergic blockade) but leave PC activity unaffected obviously disrupt spatial memory at a post-PC level. Situations creating a conflict between egocentric and allocentric orientation (place navigation in the Morris water maze filled with slowly rotating water) slow down spatial learning. PC recording in rats searching food pellets in a rotating arena makes it possible to determine which firing fields are stable relative to the room (allocentrically dependent on sighted extramaze landmarks), to the surface of the arena (dependent on egocentric path integration mechanisms and intra-arena cues), or disappear during rotation. Such comparison is made possible by the computerized tracking system simultaneously displaying a rat's locomotion and the respective firing rate maps both in the room reference and arena reference frames. More severe conflict between allocentric and egocentric inputs is produced in the field clamp situation when the rat searching food in a ring-shaped arena is always returned by rotation of the arena to the same allocentric position. Ten-minute exposure to this condition caused subsequent disintegration or remapping of 70% PCs (n = 100). Simultaneous examination of PC activity and navigation is possible in the place avoidance task. A rat searching food in a stationary or rotating arena learns to avoid an allocentrically or egocentrically defined location where it receives mild electric footshock. In the place preference task the rat releases pellet delivery by entering an unmarked goal area and staying in it for a criterion time. Both tasks allow direct comparison of the spatial reference frames used by the PCs and by the behaving animal.     

Evidence from visuomotor adaptation for two partially independent visuomotor systems.

Visual information can specify spatial layout with respect to the observer (egocentric) or with respect to an external frame of reference (allocentric). People can use both of these types of visual spatial information to guide their hands. The question arises if movements based on egocentric and movements based on allocentric visual information comprise 2 independent visuomotor systems. In the experiments reported here, we used visuomotor adaptation to address this question. In an adaptation phase, subjects received distorted-visual feedback about their hand movements (17° rotation and 110% amplitude stretch). In a testing phase (no-visual feedback), we measured how behavior changes in response to the distorted-visual feedback. During adaptation and testing, we used 2 tasks that required processing of either egocentric or allocentric visual information. The results show that behavioral changes are significantly larger when the same task is used during testing and adaptation, compared to when the task is switched. The findings suggest that the human brain employs 2 partially independent visuomotor systems that rely on different types of visual spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mental space travel: Damage to posterior parietal cortex prevents egocentric navigation and reexperiencing of remote spatial memories.

The ability to navigate in a familiar environment depends on both an intact mental representation of allocentric spatial information and the integrity of systems supporting complementary egocentric representations. Although the hippocampus has been implicated in learning new allocentric spatial information, converging evidence suggests that the posterior parietal cortex (PPC) might support egocentric representations. To date, however, few studies have examined long-standing egocentric representations of environments learned long ago. Here we tested 7 patients with focal lesions in PPC and 12 normal controls in remote spatial memory tasks, including 2 tasks reportedly reliant on allocentric representations (distance and proximity judgments) and 2 tasks reportedly reliant on egocentric representations (landmark sequencing and route navigation; see Rosenbaum, Ziegler, Winocur, Grady, & Moscovitch, 2004). Patients were unimpaired in distance and proximity judgments. In contrast, they all failed in route navigation, and left-lesioned patients also showed marginally impaired performance in landmark sequencing. Patients' subjective experience associated with navigation was impoverished and disembodied compared with that of the controls. These results suggest that PPC is crucial for accessing remote spatial memories within an egocentric reference frame that enables both navigation and reexperiencing. Additionally, PPC was found to be necessary to implement specific aspects of allocentric navigation with high demands on spontaneous retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Metabolism of 4,7,10,13,16,19-docosahexaenoic acid in isolated perfused adult and newborn pig eyes

In rats, hippocampal lesions result in impairment of spatial navigation, although other learning abilities remain unaltered. When learning a left/right discrimination task, rats can use a spatial strategy (with external maze landmarks-Situation 1) or are forced to use an egocentric strategy (without external or internal maze cues-Situation 2). Little is known about the extrahippocampal systems involved in the utilization of egocentric strategy. It is suggested that striatum could play an important role in the learning abilities that are spared after hippocampal lesion. The aim of our study was to investigate which strategy is used by rats bearing hippocampal or caudate-putamen lesions in the acquisition of a left/right discrimination task in an elevated T-maze in both Situations 1 and 2. We also investigated the effect of each lesion on the reversal of discrimination in both situations. Acquisition was not altered in any of the situations; however, a transfer test showed that hippocampal-lesioned rats used a different strategy (egocentric) from control animals (spatial) in Situation 1. In addition, reversal of the discrimination was impaired in Situation 2. Caudate-putamen lesion produced a transient effect on reversal of discrimination only in the egocentric task (Situation 2), but did not impair acquisition of the task in either situation, thus suggesting that the animals were able to use either strategy.     

Spatial cognitive maps: Differential role of parietal cortex and hippocampal formation.

Separate groups of rats with lesions in the parietal cortex (PC) or hippocampal formation (HF) were tested for acquisition and retention of the Morris water maze cognitive mapping task. Some of the animals in each lesion group received preoperative training in the task. Other animals in each group received no preoperative training. Results indicate that although both lesions lead to a cognitive mapping impairment in both the acquisition and retention of the task, the animals with PC lesions were more severely impaired than were the animals with HF lesions, as indicated by quantitative measures. However, qualitative aspects of the animals' swim behavior indicate that the HF damaged animals tend to use "nonmapping" strategies to solve the task, which suggests that the qualitative nature of their impairment differs from that of the PC damaged animals. Results of this study support the hypothesis that PC plays an important role in the processing of information about space that is allocentric or external to the body. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Double dissociation of egocentric and allocentric space following medial prefrontal and parietal cortex lesions in the rat.

Animals with medial prefrontal cortex or parietal cortex lesions and sham-operated and non-operated controls were tested for the acquisition of an adjacent arm task that accentuated the importance of egocentric spatial lateralization and a cheese board task that accentuated the importance of allocentric spatial localization. Results indicated that relative to controls, animals with medial prefrontal cortex lesions are impaired on the adjacent arm task but displayed facilitation on the cheese board task. In contrast, relative to controls, rats with parietal cortex lesions are impaired on the cheese board task but show no impairment on the adjacent arm task. The data suggest a double dissociation of function between medial prefrontal cortex and parietal cortex in terms of coding of egocentric versus allocentric spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of the contributions of the frontal and parietal association cortex to spatial localization in rats.

Compared 15 rats with lesions of the medial frontal, orbital frontal, or parietal cortex with 5 rats with complete removal of the neocortex and 5 normal controls on 3 spatial tasks: Morris water task, radial arm maze, and spatial reversals in a Grice box. Decortication produced severe impairments in the acquisition of all 3 tasks. Ss with parietal cortex lesions were relatively unimpaired at any of the tasks, although they had a significant deficit on the spatial reversal task and had a short-term memory impairment on the radial arm maze. In contrast, Ss with medial frontal lesions had a significant, but relatively mild, impairment on the radial arm maze and were poor at learning the water task. Ss with orbital frontal lesions were nearly as impaired on the radial arm maze and water task as decorticate Ss. Results suggest that the frontal and parietal cortex of rats play different roles in the control of spatial orientation but do not support the view that egocentric and allocentric spatial orientation are related to frontal and parietal mechanisms, respectively. In addition, results suggest that the frontal cortex plays a larger role in the control of spatially guided behavior than has been previously recognized and that both the medial frontal and the orbital frontal cortex play a dissociable role in the control of spatial orientation. (60 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurotoxic lesions of the rat perirhinal cortex fail to disrupt the acquisition of performance of tests of allocentric spatial memory.

Rats with neurotoxic lesions of the perirhinal cortex (n = 9) were compared with sham controls (n = 14) on a working memory task in the radial am maze. Rats were trained under varying levels of proactive interference and with different retention intervals. Finally, performance was assessed when the maze was switched to a novel room. None of these manipulations differentially impaired rats with perirhinal lesions. Rats were next trained on delayed matching-to-place in the water maze. Even with retention delays of 30 min, there was no evidence of a deficit. Although interactions between the perirhinal cortex and hippocampus may be important for integrating object-place information, the perirhinal cortex is often not necessary for tasks that selectively tax allocentric spatial memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory for Visuospatial Location Following Selective Hippocampal Sclerosis: The Use of Different Coordinate Systems.

This study addressed the role of the medial temporal lobe regions and, more specifically, the contribution of the human hippocampus in memory for body-centered (egocentric) and environment-centered (allocentric) spatial location. Twenty-one patients with unilateral atrophy of the hippocampus secondary to long-standing epilepsy (left, n = 7; right, n = 14) and 15 normal control participants underwent 3 tasks measuring recall of egocentric or allocentric spatial location. Patients with left hippocampal sclerosis were consistently impaired in the allocentric conditions of all 3 tasks but not in the egocentric conditions. Patients with right hippocampal sclerosis were impaired to a lesser extent and in only 2 of the 3 tasks. It was concluded that hippocampal structures are crucial for allocentric, but not egocentric, spatial memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The cerebellum in the spatial problem solving: a co-star or a guest star?

The experimental findings reviewed here indicate that the cerebellum has to be added to the regions known to be involved in the spatial learning. Cerebellar function is specifically linked to 'how to find an object' rather than 'where the object is in the space'. In the Morris water maze (MWM) hemicerebellectomized (HCbed) rats displayed a severe impairment in coping with spatial information, displaying only peripheral circling. And yet, when the MWM cue phase was prolonged, HCbed rats succeeded in acquiring some abilities to learn platform position, even in a pure place paradigm, such as finding a hidden platform with the starting points sequentially changed. Conversely, whether the searching strategy was acquired preoperatively, no exploration deficit appeared. Thus, cerebellar lesions appear to affect the procedural components of spatial function, sparing the declarative ones. When intact animals were non-spatially pre-trained and then HCbed, they exhibited an expanded scanning strategy, underlining the cerebellar involvement in procedural component acquisition. By testing HCbed rats in an active avoidance task, first without and then with a request for right/left discrimination, lesioned rats displayed severe deficits. Thus, besides a marked impairment in facing procedural components of spatial processing, cerebellar lesion provokes deficits also in right/left discrimination task. In conclusion, it is possible to propose the cerebellum as one part of a large system that includes frontal, posterior parietal, inferior temporal cortices, hippocampus and basal ganglia. These structures form an allocentric spatial system and an egocentric control system, that interlock to process the information involved in representing an object in the space.     

Functionally dissociating aspects of event memory: the effects of combined perirhinal and postrhinal cortex lesions on object and place memory in the rat

Reciprocal interactions between the hippocampus and the perirhinal and parahippocampal cortices form core components of a proposed temporal lobe memory system. For this reason, the involvement of the hippocampus in event memory is thought to depend on its connections with these cortical areas. Contrary to these predictions, we found that NMDA-induced lesions of the putative rat homologs of these cortical areas (perirhinal plus postrhinal cortices) did not impair performance on two allocentric spatial tasks highly sensitive to hippocampal dysfunction. Remarkably, for one of the tasks there was evidence of a facilitation of performance. The same cortical lesions did, however, disrupt spontaneous object recognition and object discrimination reversal learning but spared initial acquisition of the discrimination. This pattern of results reveals important dissociations between different aspects of memory within the temporal lobe. Furthermore, it shows that the perirhinal-postrhinal cortex is not a necessary route for spatial information reaching the hippocampus and that object familiarity-novelty detection depends on different neural substrates than do other aspects of event memory.     

Preoperative chemotherapy followed by concurrent chemoradiation therapy based on hyperfractionated accelerated radiotherapy and definitive surgery in locally advanced non-small-cell lung cancer: mature results of a phase II trial

The ability of rats to learn the location of a hidden platform in a swim maze was compared in animals with excitotoxic lesions of the anterior or posterior (retrosplenial) cingulate cortex or radiofrequency lesions of the cingulum bundle or fimbria-fornix. Performance of this allocentric spatial task was unaffected by the posterior cingulate cortex lesions, while anterior cingulate cortex damage produced only a mild acquisition deficit. Transection of the fornix and lesions of the cingulum bundle produced similar patterns of impairment on initial acquisition, but the cingulum bundle lesions had less effect on reversal of the task. The results from the water maze, and from a subsequent T-maze alternation task, indicate that cingulum bundle lesions can produce a spatial deficit that is similar, but milder, to that observed after fornix transection. The results of the excitotoxic lesions suggest that previous studies examining conventional cingulate lesions may have been influenced by damage to adjacent fibre tracts, such as the cingulum bundle.     

Newborn organ weight and spontaneous hypertension: recombinant inbred strain study

This study investigated the effects of neonatal hippocampal ablation on the development of spatial learning and memory abilities in rats. Newborn rats sustained bilateral electrolytic lesions of the hippocampus or were sham-operated on postnatal day 1 (PN1). At PN20-25, PN50-55, or PN90-95, separate groups of rats were tested in a Morris water maze on a visible "cue" condition (visible platform in a fixed location of the maze), a spatial "place" condition (submerged platform in a fixed location), or a no-contingency "random" condition (submerged platform in a random location). Rats were tested for 6 consecutive days, with 12 acquisition trials and 1 retention (probe) trial per day. During acquisition trials, the rat's latency to escape the maze was recorded. During retention trials (last trial for each day, no escape platform available), the total time the rat spent in the probe quadrant was recorded. Data from rats with hippocampal lesions tested as infants (PN20-25) or as adults (PN50-55 and PN90-95) converged across measures to reveal that 1) spatial (place) memory deficits were evident throughout developmental testing, suggesting that the deficits in spatial memory were long-lasting, if not permanent, and 2) behavioral performance measures under the spatial (place) condition were significantly correlated with total volume of hippocampal tissue damage, and with volume of damage to the right and anterior hippocampal regions. These results support the hypothesis that hippocampal integrity is important for the normal development of spatial learning and memory functions, and show that other brain structures do not assume hippocampal-spatial memory functions when the hippocampus is damaged during the neonatal period (even when testing is not begun until adulthood). Thus, neonatal hippocampal damage in rats may serve as a rodent model for assessing treatment strategies (e.g., pharmacological) relevant to human perinatal brain injury and developmental disabilities within the learning and memory realm.     

Spatial encoding of hidden objects in dogs (Canis familiaris).

The authors investigated the type of spatial information that controls domestic dogs' (Canis familiaris) search behavior in a situation in which they have to locate a spatial position where they saw an object move and disappear. In Experiments 1 and 2, the authors manipulated all local and global sources of allocentric spatial information surrounding the hiding location. The results revealed that dogs relied on an egocentric frame of reference. Experiment 3 showed that dogs also encoded allocentric information when egocentric information was irrelevant. The authors conclude that dogs simultaneously encode both egocentric and allocentric spatial information to locate a spatial position, but they primarily base their search behavior on an egocentric frame of reference. The authors discuss under which natural conditions dogs might use these 2 sources of spatial information and detail the nature of spatial egocentric information and the circumstances underlying its use by dogs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of selective immunotoxic lesions of medial septal cholinergic cells on spatial working and reference memory.

The effect of injection into the medial septum of a toxin selective for cholinergic neurons, 192 IgG-saporin, was examined in rats trained to perform 2 versions of the radial 8-arm maze task. Rats were first trained to perform a task with varying delays (0, 1, 2 min) imposed between the 4th correct arm choice and access to all 8 arms. Lesioned rats made significantly more errors in the first 4 choices compared with controls and significantly more errors after delays; however, this effect was not delay dependent. Rats were then trained on a different version of this 8-arm maze task in which they learned to avoid 2 arms that were never baited. There was no treatment effect on acquisition of this task. These data are consistent with the hypothesis that the cholinergic projection to the hippocampus facilitates the acquisition of information into the system responsible for short-term memory for locations visited (spatial working memory) but is not involved in retention of this information. It also appears to play no role in either the acquisition or retention of place-nonreward associations (spatial reference memory). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Place memory is intact in rats with perirhinal cortex lesions.

Two experiments compared the effects of bilateral lesions of the hippocampal formation (HPC) or perirhinal cortex (PRh) on rats' performance of an allocentric spatial working memory task—delayed matching-to-place (DMTP) in a water maze. DMTP trials consisted of paired swims, and the hidden platform was moved to a new location on each trial. Performance was assessed with intervals between the first and second swim (i.e., retention delays) of 4, 30, 120, and 300 s. The rats received extensive presurgery training in Experiment 1 and no presurgery training in Experiment 2. In both experiments, rats with HPC lesions displayed DMTP deficits at all delays, taking longer and swimming farther to find the platform on the second swims than did sham-operated controls. By contrast, rats with PRh lesions displayed normal DMTP acquisition and performance. The results suggest that, unlike the functions of HPC, those of PRh are not critical for allocentric spatial working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)