Deficits in allothetic and idiothetic spatial behavior in rats with posterior cingulate cortex lesions.

The cingulate cortex plays a central role in bridging neocortical and limbic structures involved in allothetic navigation, a form of navigation requiring the use of external cues. Animals can also navigate using idiothetic cues, which are cues generated by self-movement, but there have been no definitive tests of whether cingulate cortex also plays a role in idiothetic navigation. Rats with anterior cingulate (medial frontal) and posterior cingulate cortex (retrosplenial) suction ablations were trained to search for large food pellets on an open table, and the accuracy with which they returned home with the food was measured. In the idiothetic task they searched for food from a novel starting location under infrared light, and with surface olfactory cues displaced. The rats also received two tests of allothetic navigation. They were tested on a matching-to-place task in which they foraged for food from a number of successively presented new locations under normal room light, and they were trained to locate a hidden platform in a swimming pool (Morris place task). The group with posterior cingulate cortex lesions was severely impaired on all of the navigation tasks whereas the group with anterior cingulate cortex lesions displayed no deficit on the idiothetic task and only moderate deficits on the other tasks. The results demonstrate a role for posterior cingulate region in idiothetic navigation.

Hippocampectomized rats are impaired in homing by path integration.

Theoretical, behavioral, and electrophysiologic evidence suggests that the hippocampal formation may play a role in path integration, a form of spatial navigation in which an animal can return to a starting point by integrating self-movement cues generated on its outward journey. The present study examined whether the hippocampus (Ammon's horn and the dentate gyrus) is involved in this form of spatial behavior. Control rats and rats with selective ibotenic acid lesions of the hippocampus were tested in a foraging task in which they retrieved large food pellets from an open field, which when found, they carried to a refuge for consumption. The experiments measured the rats' homing accuracy, returning to the starting location, under conditions in which visual, surface, and self-movement cues; surface and self-movement cues; or only self-movement cues were available. Although both control rats and rats without a hippocampus could use visual and surface cues, only control rats appeared to be able to use self-movement cues. The finding that hippocampal rats are impaired under conditions requiring the use of self-movement cues suggests that the hippocampus plays an essential role in path integration.

Homing with locale, taxon, and dead reckoning strategies by foraging rats: sensory hierarchy in spatial navigation.

Studies on foraging rats suggest that they can use visual, olfactory, and self-movement cues for spatial guidance, but their relative reliance on these different cues is not well understood. In the present study, rats left a hidden refuge to search for a large food pellet located somewhere on a circular table, and the accuracy with which they returned to the refuge with the food pellet was measured. Cue use was manipulated by administering probe trials from novel locations, blindfolding, moving the home cage relative to the table, rotating the table and using combinations of these manipulations. When visual cues were available and a consistent starting location used, a visual strategy dominated performance. When blindfolded, the rats used olfactory cues from the surface of the table and from the starting hole. When olfactory stimuli were made uninformative, by changing the starting hole and rotating the table, the rats still homed accurately, suggesting they used self-movement cues. In a number of cue combinations, in which cues gave conflicting information, performance degraded. The results suggest that rats display a hierarchical preference in using visual, olfactory and self-movement cues while at the same time being able to reaffirm or switch between various cue combinations. The results are discussed in relation to ideas concerning the neural basis of spatial navigation.

Rats with fimbria-fornix lesions are impaired in path integration: a role for the hippocampus in "sense of direction".

Animals can locate their present position in relation to a starting point and return to that starting point using cues generated by self-movement, a navigation strategy called dead-reckoning. Because contemporary research on spatial navigation suggests that some aspects of spatial navigation depend on the integrity of the hippocampal formation, whereas others do not, the present study examined whether dead-reckoning is hippocampally dependent. The task capitalized on the proclivity of foraging rats to carry large food pellets to a shelter for eating. Control rats and rats with fimbria-fornix (FF) lesions left a hidden burrow to search for one piece of food located somewhere on a circular table. The accuracy with which they returned to the burrow with the food was measured. In three experiments, rats received probe trials in which they (1) started from novel locations, (2) wore blindfolds to obscure visual cues, and (3) foraged under a condition in which surface cues, e.g., odors left by their outward searches, were displaced. Both sighted control and FF rats preferentially used visual cues for guidance when foraging from a familiar location. Control rats were accurate and FF rats were impaired in returning to novel starting locations (1) when sighted, (2) when blindfolded, and (3) when blindfolded in tests in which surface cues were displaced. These results, as well as detailed observations on the behavior of the animals, are consistent with the hypothesis that rats can use dead-reckoning to solve spatial problems, and this ability depends on the integrity of the hippocampal formation.

Executive function of the hippocampus in social behavior in the rat.

Bilateral lesion of the fimbria resulted in a reduction of social interdependency and agonistic behavior in male-male encounters in rats. These findings are hypothesized to be consistent with J. A. Gray's (1982) supervisor model, which assigns an executive function to the septohippocampal system. To achieve this interpretation, social behavior is described in terms of relational processes (social hypothesis, behavioral sequencing, and behavioral competition). This study focused mainly on the effects of the lesion on behavioral sequencing by studying the alterations of the predictability of the behavior of a rat in terms of the behavior of its partner.

Hippocampal lesions and path integration.

Research on spatial problem-solving over the past two years has linked the hippocampus to path integration, that is, the use of movement-related cues to guide spatial behavior. Path integration may underlie the forms of place learning that are impaired by hippocampal damage. It remains a challenge to determine whether path integration is the central function of the hippocampus or but one of many.

Effects of an electrolytic lesion of the prelimbic area on anxiety-related and cognitive tasks in the rat.

The aim of this paper was to study the role of the prelimbic area of rats in response selection. A bilateral electrolytic lesion was made in the prelimbic area. The rats were tested in the Morris water-maze, the conditioned shock-prod burying test, the elevated plus-maze, a modified open field test, and the step-through passive avoidance test. In the water-maze during initial acquisition, the latency times of the lesioned rats were not different from those of the controls, but they found the platform faster than the sham operated rats after the platform was placed in a new position. The lesion did not affect performance in the shock-prod burying test. In the elevated plus-maze the lesioned rats were more active than the sham-operated rats and spent more time on the open arms. In the open field there was no difference between lesioned and sham-operated rats with regard to distance travelled or the time spent near the object in the center of the open field. In the passive avoidance test the lesioned rats had a shorter latency time to enter the shock compartment during the retention trial than the sham-operated rats did. The results were discussed in relation to those of similar studies. The extent and precise localisation of the lesion seems to be crucial for the outcome: lesions confined to the prelimbic area may have the opposite effects of larger lesions. Furthermore, it may well be that the prelimbic area is only involved in processing of stimuli of a specific sensory modality, as made probable by the results of different conditioned reinforcement tasks. Finally, it was stated that we still lack a hypothesis about the precise role of the prelimbic area in response selections.

Roles of the basolateral amygdala and hippocampus in social recognition in rats.

Lesions of the amygdala or hippocampus have a large impact on social behavior of rats. In this study we investigated whether a social recognition test was also affected by those lesions. An NMDA-induced lesion of the basolateral amygdala did not impair the ability to distinguish a familiar from an unfamiliar juvenile rat. It was argued that the cortico-medial amygdala may be more important for social recognition than the basolateral amygdala. Fimbria-transected rats could no longer distinguish a familiar from an unfamiliar juvenile. Moreover, during all encounters they spent less time investigating the juvenile. The precise nature of this deficit, especially the reason for the overall reduced social investigation time, could not be specified with the classical procedure of the social recognition test.

The ACTH(4-9) analog Org2766 modulates the behavioral changes induced by NMDA and the NMDA receptor antagonist AP5.

In studies on aged and brain-lesioned rats the chronic administration of the ACTH(4-9) analog Org2766 has been demonstrated to improve the behavioral performance. Those results suggest that maintenance of hippocampal functioning in senescence and facilitation of functional recovery after brain damage are not due to facilitated reinnervation of denervated structures as suggested in previous studies concerning regeneration of the PNS. Alternative explanations may refer to either the neuroprotective properties of the peptide as demonstrated when chronic treatment immediately follows the damage, or a peptide-induced general change in attention that indirectly may contribute to functional recovery. The behavioral effects after acute treatment with ACTH-like peptides have been previously associated with sustained attention by enhanced neuronal excitability of limbic structures. Now, a hypothesis accounting for both neuroprotection and enhanced attention is forwarded by supposing that the peptide exerts its influence by modulation of NMDA receptor activation. Therefore, the acute effects and interactions between the peptide and the NMDA receptor antagonist AP5 (D,L-2-amino-5-phosphonopentanoic acid), and the peptide and NMDA were studied in a water maze and an open field. Impaired water maze performance induced by an acute intracerebroventricular administration of AP5 was counteracted by the ACTH(4-9) analog Org2766, whereas the peptide alone did not affect spatial orientation. NMDA induced extreme locomotor activity at the periphery of the open field. Interestingly, the ACTH(4-9) analog strongly suppressed NMDA-induced enhanced locomotor activity and normalized the pattern of exploratory behavior.