Dissociation of spatial discrimination deficits following frontal and parietal lesions in monkeys.

Gave 40 rhesus monkeys dorsolateral prefrontal, posterior parietal, or inferotemporal lesions. 4 additional Ss served as unoperated controls. Ss then received 2 forms of spatial discrimination training, based on body position ("egocentric" cues) and on the position of an external referent ("allocentric" cues), respectively. On the former, a place discrimination reversal, frontal Ss were impaired but not parietals. On the latter, a landmark discrimination reversal, parietal Ss were impaired but not frontals; this result was also obtained on a test involving distance discrimination without reversal. Finally, the inferotemporals but not the frontals or parietals were impaired on a nonspatial object discrimination reversal. Results suggest that the 2 modes of spatial orientation, egocentric and allocentric, are related to frontal and parietal mechanisms, respectively. (18 ref.) (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)     

Spatial behavior in gerbils (Meriones unguiculatus).

Investigated whether adult gerbils could use an allocentric frame of reference to efficiently solve a spatial memory task. 38 male Ss were allowed to explore an arena containing an object. The external reference frame was reduced to a single visual landmark. After habituation, Ss entered the arena from a new direction. A 2nd object, identical to the 1st object, was placed symmetrically with regard to the landmark. The 2nd object was explored more than the 1st object, a result showing that the 2nd object was differentiated on the basis of location. This result suggests that, during the course of exploration, Ss had learned about the spatial features of the experimental situation. It is suggested that Ss' final discrimination performance (preference for the novel stimulus location) reflected an allocentric rather than egocentric frame of reference. (15 ref) (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)     

Effects of haloperidol and d-amphetamine on working and reference memory performance in a spatial cone field task

The present study was designed to examine the effects of haloperidol (0.03, 0.1 mg/kg, intraperitoneal (i.p.)) and d-amphetamine (0.3, 1.0 mg/kg, i.p.) in a cone field task in which spatial working and reference memory (WM and RM, respectively) were assessed simultaneously. The apparatus is a large open field in which 16 cones are placed with four cones baited by placing a food reward in the top. After food-deprived rats had acquired this task they showed a high level of performance, that is avoided visits to non-baited cones (RM) and made few revisits to baited cones (WM). Haloperidol had a greater negative effect on RM than on WM performance, but also decreased the number of food rewards collected. On the other hand, the high dose of d-amphetamine induced a clear WM performance deficit, whereas RM performance was only marginally affected. The present study suggests that spatial discrimination performance can be dissociated using the measures RM and WM in the present task. Further, the deficits induced by haloperidol and d-amphetamine may not be specifically related with impaired mnemonic functions.     

Effects of repeated disorientation on the acquisition of spatial tasks in rats: Dissociation between the appetitive radial arm maze and aversive water maze.

This study examined the effects of disorientation on the acquisition of different spatial reference memory tasks. In an appetitively motivated radial arm maze task in which 1 arm was consistently baited, rats that were disoriented before each trial were impaired in their ability to acquire the task relative to rats placed in a clear container and not disoriented. However, disoriented rats were able to learn a Morris water maze and a water version of the radial arm maze under similar training conditions, suggesting that the effects of disorientation may interact with the quality or quantity of motivation involved in a given task. These results suggest that appetitive and aversive spatial tasks are dissociable, and that any impairment that is due to disorientation is specific to the appetitive radial arm maze task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial learning deficit and reduced hippocampal ChAT activity in rats after an ICV injection of streptozotocin

ICV injections of streptozotocin (STREP) lower the glucose utilization of the brain and affect the cholinergic system. The present study was designed to evaluate whether STREP-treated rats have an impaired spatial discrimination performance in the Morris spatial navigation task. Performance in this task is sensitive to treatment with cholinergic antagonists. In contrast to young rats, middle-aged STREP-treated rats tended to have an impaired spatial discrimination performance in the Morris task at the end of training. In middle-aged STREP-treated rats, but not in control rats, spatial discrimination performance was associated with hippocampal choline acetyltransferase (ChAT) activity. The correlation between spatial discrimination performance in the Morris task and the decrease in hippocampal ChAT activity resembles the relation between cognitive and biochemical changes observed in Alzheimer's disease. Our findings suggest that STREP treatment of middle-aged rats may provide a relevant model for dementia.     

Orangutan (Pongo pygmaeus abelii) spatial memory and behavior in a foraging task.

Orangutan (Pongo pygmaeus abelii) spatial memory was explored by using an arboreal foraging paradigm in a zoo environment. The experiment consisted of 4 tasks: walking maze, win-stay, food density, and competition. All 3 orangutans made very few revisits to previously depleted sites in the walking maze task. In the win-stay task, 2 orangutans were more accurate than chance at remembering locations of specific baited sites. Food density affected the behavior of 1 orangutan. Foraging with a competitor did not increase the orangutans' accuracy at recovering food from baited locations. The orangutans did not compete directly for access to the food sites but did avoid visiting sites depleted by a competitor. The orangutans' foraging patterns suggest that they minimized energy expended by reducing the distance traveled to retrieve food items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extensive cytotoxic lesions of the rat retrosplenial cortex reveal consistent deficits on tasks that tax allocentric spatial memory.

Despite the connections of the retrosplenial cortex strongly suggesting a role in spatial memory, the lesion data to date have been equivocal. Whether subjects are impaired after retrosplenial lesions seems to depend on whether the lesions were aspirative or excitotoxic, with the latter failing to produce an impairment. A shortcoming of previous excitotoxic lesion studies is that they spared the most caudal part of the retrosplenial cortex. The present study thus used rats with extensive neurotoxic lesions of the retrosplenial cortex that encompassed the entire rostrocaudal extent of this region. These rats were consistently impaired on several tests that tax allocentric memory. In contrast, they were unimpaired on an egocentric discrimination task. Although the lesions did not appear to affect object recognition, clear deficits were found for an object-in-place discrimination. The present study not only demonstrates a role for the retrosplenial cortex in allocentric spatial memory, but also explains why previous excitotoxic lesions have failed to detect any deficits. (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)     

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 opposite effects on cysteamine on the acquisition of two different tasks in mice are associated with bidirectional testing-induced changes in hippocampal adenylyl cyclase activity.

The hypothesis of a role for hippocampal somatostatin (SS-14) in learning and memory processes was further examined by means of 2 selective learning tasks that were previously shown to be either impaired (spatial discrimination task) or facilitated (barpressing task) by hippocampal lesions. Results showed that subcutaneous injections of cysteamine (160 mg/kg) (a) impaired acquisition of the spatial task while producing an opposite (i.e., facilitative) effect on acquisition of the barpressing task and (b) produced an up regulation of hippocampal adenylyl cyclase (AC) activity, which was antagonized by spatial discrimination training but enhanced by training in the barpressing task. Moreover, opposite task-dependent training induced changes in hippocampal AC activity was observed in saline-treated mice. These results suggest that bidirectional regulatory mechanisms of hippocampal function involving both SS-14 and ACs may occur as a function of the type of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intramaze and Extramaze Cue Processing in Adult APPSWE Tg2576 Transgenic Mice.

The present study examined spatial and nonspatial learning in adult Tg2576 mice. Transgenic mice were impaired in acquisition of a T-maze forced-choice alternation task. However, mutant mice were as sensitive as control mice to the introduction of retention intervals and proactive interference, and this suggested that short-term memory processes were intact in Tg2576 mice. Probe trials revealed that the Tg2576 mice did not use an allocentric strategy to navigate to the goal arm. However, mutant mice acquired an intramaze brightness discrimination, a simple room discrimination, and a contextual biconditional left-right discrimination in a T maze. Results suggest that Tg2576 mice are able to process both intramaze and extramaze stimuli but are impaired in forming an allocentric representation of their environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the fornix and anterior thalamic nuclei dissociate different aspects of hippocampal-dependent spatial learning: Implications for the neural basis of scene learning.

The present study used 2 different discrimination tasks designed to isolate distinct components of visuospatial learning: structural learning and geometric learning. Structural learning refers to the ability to learn the precise combination of stimulus identity with stimulus location. Rats with anterior thalamic lesions and fornix lesions were unimpaired on a configural learning task in which the rats learned 3 concurrent mirror-image discriminations (structural learning). Indeed, both lesions led to facilitated learning. In contrast, anterior thalamic lesions impaired the geometric discrimination (e.g., swim to the corner with the short wall to the right of the long wall). Finally, both the fornix and anterior thalamic lesions severely impaired T-maze alternation, a task that taxes an array of spatial strategies including allocentric learning. This pattern of dissociations and double dissociations highlights how distinct classes of spatial learning rely on different systems, even though they may converge on the hippocampus. Consequently, the findings suggest that structural learning is heavily dependent on cortico-hippocampal interactions. In contrast, subcortical inputs (such as those from the anterior thalamus) contribute to geometric learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Using Idiothetic Cues to Swim a Path With a Fixed Trajectory and Distance: Necessary Involvement of the Hippocampus, but Not the Retrosplenial Cortex.

Rats rapidly learned to find a submerged platform in a water maze at a constant distance and angle from the start point, which changed on every trial. The rats performed accurately in the light and dark, but prior rotation disrupted the latter condition. The rats were then retested after receiving cytotoxic hippocampal or retrosplenial cortex lesions. Retrosplenial lesions had no apparent effect in either the light or dark. Hippocampal lesions impaired performance in both conditions but spared the ability to locate a platform placed in the center of the pool. A hippocampal deficit emerged when this pool-center task was run in the dark. The spatial effects of hippocampal damage extend beyond allocentric tasks to include aspects of idiothetic guidance. (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)     

Food searching strategies of rats: Variables affecting the relative strength of stay and shift strategies.

Examined the extent to which the food searching strategies of rats are influenced by training, information about food in an initially visited site, and type of memory required for correct choices. Exp I used a discrete-trial, delayed conditional-discrimination procedure on a T-maze with 32 male Sprague-Dawley rats. Ss entered 1 arm of the maze and were given a choice between that arm (stay strategy) or the other arm (shift strategy). During the initial visit, S either consumed all the food (depletion condition) or only some of it (nondepletion condition). Ss given the shift-depletion task learned most rapidly; those given the stay-depletion task learned most slowly. Depletion increased the rate at which the shift discrimination was learned but decreased the rate at which the stay discrimination was learned. Exp II used a similar procedure with the Maier 3-table maze and 16 male albino rats; the same pattern of results was found. Exp III, conducted with 15 male Sprague-Dawley rats, required each S to learn both a win-stay and a lose-shift contingency and to use associative memory. Early in training, Ss used only a shift strategy but eventually learned the discrimination. Results indicate that the shift-stay balance is influenced by the rat's species-specific predisposition, reinforcement contingencies, amount of food in the initially visited place, and the extent to which recognition memory by itself is sufficient to solve the discrimination. (48 ref) (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)     

Marmoset (Callithrix jacchus jacchus) spatial memory in a foraging task: Win-stay versus win-shift strategies.

The spatial memory of common marmosets (Callithrix jacchus jacchus) was explored in 3 experiments with a simulated foraging task. In Experiment 1, individual monkeys foraged among 8 baited food sites. They appeared to use spatial memory to accurately avoid revisiting previously depleted sites. There was no difference in accuracy between the adult monkeys and a juvenile monkey tested on the same task. In Experiment 2, a win–stay paradigm was used. The adult monkey subject very accurately remembered locations that had previously contained food. The monkey tended to visit adjacent correct sites when retrieving food and thus minimized the total distance travelled. In Experiment 3, a win–shift paradigm was used with 2 adult monkeys. Although both monkeys performed at above-chance levels of accuracy on the win–shift task, they made many errors. These results suggest that marmosets may prefer tasks that require a win–stay strategy. (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)