The moving fire hydrant experiment: movement of objects to a new location reelicits marking in rats

Three experiments were carried out to investigate the influence of object relocation on object marking in an open field by hooded and albino rats. Object marking was reelicited when an object was moved to a new location in the second half of an open field test. Control conditions revealed that an object briefly moved and returned to the original location elicited no more marking than a stationary object. The higher level of marking of the relocated object suggests that object marking may provide an index of spatial knowledge. The implication of spatial knowledge in controlling marking behavior is congruent with observations that rats with hippocampal damage show increased marking.     

Scent marking by male dwarf hamsters (Phodopus sungorus campbelli) in response to conspecific odors

Male hamsters (Phodopus sungorus campbelli) scent marked at greater frequencies in the presence of conspecific odor, either male or female, than in clean areas. Marking rates were not different between male and female odor conditions. In contrast, the pattern of investigation in response to conspecific odor did differ between the male and the female odor conditions. When male odors were used as stimuli, investigative sniffing increased at the scent marking sites but when female odors were used as stimuli investigative sniffing increased throughout the arena. Thus, male dwarf hamsters direct their scent marks at both male and female conspecifics, discriminate between male and female odor, and investigate in a different manner areas scent marked by males and females.     

Training method dramatically affects the acquisition of a place response in rats with neurotoxic lesions of the hippocampus.

A considerable number of studies have demonstrated that hippocampal damage impairs the acquisition of a place response in rats. In Experiment 1, using a four-arm plus-shaped maze, we replicated this finding. Experiment 2 showed, however, that hippocampally damaged rats can learn a place response just as well as control rats when, during the training, a salient intramaze landmark indicates the position of the goal (the west arm). After reaching criterion, the hippocampal and control groups performed the task with the same degree of mastery during a transfer test in which the intramaze signal used during the acquisition was removed. In Experiment 3, the intramaze cue was substituted by an egocentric cue. The results revealed that both control and lesioned subjects learned the spatial problem well. However, a transfer test showed that control rats learned the task using a place response strategy but hippocampally lesioned animals used a rigid, hyperspecific strategy. Taken together, these results suggest that special training procedures which encourage variability in response versus perseveration make it possible to overcome the acquisition deficit normally observed in hippocampal rats.     

Cytotoxic lesions of the hippocampus do not impair social recognition memory in socially housed rats

Socially housed mice with cytotoxic lesions of the hippocampus do not exhibit social recognition memory 30 min following exposure to a juvenile mouse, however the social recognition memory of singly housed rats is unimpaired. The present study tests the hypothesis that social housing of rats could render social recognition memory hippocampally dependent as seen for mice. Rats were housed with juveniles or with adults. Two social recognition one-animal tests paralleling those used with mice were carried out. Seven social discrimination two-animal tests were also given. Sham operated and hippocampally lesioned rats had normal social memory at 30 min whether socially housed for 24, 48 h, 7 or 8 days prior to testing. These findings support other results indicating the hippocampus proper is not required for normal social memory in rats. In a final experiment, rats socially housed in groups of three since weaning, were tested for 30 min and 24 h social memory. Unlike mice, rats socially housed throughout life exhibited social memory only at 30 min, but not at 24 h. Manipulations that extend social memory in rats may be required to render social memory hippocampally dependent or rats and mice may differ in the neural mediation of social memory.     

Hippocampal damage and exploratory preferences in rats: memory for objects, places, and contexts

Rats have a natural tendency to spend more time exploring novel objects than familiar objects, and this preference can be used as an index of object recognition. Rats also show an exploratory preference for objects in locations where they have not previously encountered objects (an index of place memory) and for familiar objects in contexts different from those in which the objects were originally encountered (an index of context memory). In this experiment, rats with cytotoxic lesions of the hippocampal formation were tested on all three versions of the novelty-preference paradigm, with a 5-min retention interval between the familiarization and test phases. Rats with sham lesions displayed a novelty preference on all three trial types, whereas the rats with hippocampal lesions displayed a novelty preference on Object trials but did not discriminate between the objects on Place trials or Context trials. The findings indicate that hippocampal damage impairs memory for contextual or spatial aspects of an experience, whereas memory for objects that were part of the same experience are left relatively intact.     

Suppression of corticosterone synthesis alters the behavior of hippocampally lesioned rats

The suppression of corticosterone synthesis with metyrapone (25 mg/kg) reduced the hyperactivity and altered the exploratory activity of hippocampally lesioned animals (HPC) in the open field to the level of cortical and sham controls (Experiment 1). In a second experiment, corticosterone (600 micrograms/kg) pretreatment 2 h, but not 1 h, before metyrapone partially restored the hyperactivity of HPC animals that had been decreased by the corticosteroid-suppressant drug. Alterations in exploratory behavior induced by metyrapone were also prevented by corticosterone pretreatment. The results suggest that the suppression of corticosterone in hippocampally lesioned animals produces a normalization of behavior that can be prevented by pretreatment with corticosterone.     

Environmental influences on flank marking and urine marking by female and male rats (Rattus norvegicus)

Sprague-Dawley rats (Rattus norvegicus) were observed in a familiar environment. In Experiment 1 a leader entered a clean chamber, and an opposite-sex follower entered the chamber next. Both sexes began to flank mark after several sessions. Males flank marked more, and females locomoted more, but both sexes urine marked and investigated objects equally often. Leaders and followers did not differ on any measure. In Experiment 2 we measured floor marks more precisely and manipulated the number of objects and the presence of scent marks. Flank marking was more frequent in the presence of conspecific urine but did not vary with the number of objects or the sex of the rats. More objects elicited more investigating and urine marking and produced fewer floor marks but increased the number of marks in the central area in relation to the periphery. The results indicate that rats' flank marking is behaviorally distinct from urine marking and differentially affected by environmental variables.     

The effects of clozapine on delayed spatial alternation deficits in rats with hippocampal damage

Clozapine is an atypical antipsychotic drug that has been shown to improve spatial memory in some animal models; however its efficacy in reversing spatial memory impairment in rats with hippocampal lesions is unknown. To address this issue, we tested the effects of clozapine on delayed spatial alternation deficits in rats with hippocampal damage in three separate experiments. In each experiment, adult male rats received sham surgery or direct stereotaxic infusions of the excitotoxin, NMDA, into the hippocampus. In the first study, seven days after surgery, the sham control animals received daily saline injections while the lesioned animals were split into two groups that received daily saline or clozapine (2.0 mg/kg, sc) injections. During the fifth week of injections, all animals were tested in a food-motivated delayed spatial alternation task. Saline-treated rats with excitotoxic hippocampal damage displayed significant deficits in delayed spatial alternation. Daily clozapine injections completely reversed this deficit. In a second experiment, it was found that clozapine treatment limited to the testing days only did not improve alternation performance in lesioned rats. Finally, in a third experiment, chronic clozapine treatment did not improve alternation performance in lesioned rats that were pre-trained in the alternation task prior to surgery. These results suggest that chronic, but not acute, clozapine treatment enables rats with hippocampal damage to develop new spatial learning, but can not rescue old spatial learning established prior to damage. These results may have implications for the treatment of cognitive deficits caused by hippocampal dysfunction in disorders such as schizophrenia, Alzheimer's disease, and others.     

The residual spatial abilities of hippocampally lesioned rats can be enhanced by peripheral sympathetic-adrenal interventions

In order to test the possible effectiveness of peripheral interventions with the adrenergic system for the alleviation of certain disorders that typically follow bilateral hippocampal lesions, rats with bilateral lesions of the hippocampus, the overlying neocortex, or sham operations were tested at two postoperative times in the Morris water maze, a frequently used "spatial task." Half of the animals in all groups were exposed to the adrenergic manipulations, i.e., a chronic, 7-day, systemic bretylium regime (5 mg/kg) and, in addition, a peripheral injection of norepinephrine (4 micrograms/kg) 30 min before the start of each training day. The other half received saline chronically and a single saline injection before each training day. Five days of training were given at each of the two training periods. The first began 7 days after surgery while the second began 33 days after surgery. As expected, the hippocampally lesioned animals were severely impaired in the task. The adrenergic treatment produced enhanced performances in the rats with hippocampal lesions at both training sessions, although the improvement was greatest at the later period. Although the animals receiving the pharmacologic treatment located the general area of the hidden platform better than the saline-treated animals with hippocampal lesions, the treated animals were still impaired, swimming directly to the hidden platform on fewer trials than did animals in the other groups.     

Conjunctive representations in learning and memory: principles of cortical and hippocampal function

The authors present a theoretical framework for understanding the roles of the hippocampus and neocortex in learning and memory. This framework incorporates a theme found in many theories of hippocampal function: that the hippocampus is responsible for developing conjunctive representations binding together stimulus elements into a unitary representation that can later be recalled from partial input cues. This idea is contradicted by the fact that hippocampally lesioned rats can learn nonlinear discrimination problems that require conjunctive representations. The authors' framework accommodates this finding by establishing a principled division of labor, where the cortex is responsible for slow learning that integrates over multiple experiences to extract generalities whereas the hippocampus performs rapid learning of the arbitrary contents of individual experiences. This framework suggests that tasks involving rapid, incidental conjunctive learning are better tests of hippocampal function. The authors implement this framework in a computational neural network model and show that it can account for a wide range of data in animal learning.     

A Longitudinal Investigation of Object Relations: Child-Rearing Antecedents,Stability in Adulthood,and Construct Validation

Object relations theories posit that a child's relationship with caregivers has implications for subsequent relationships. Object relations refer to mental representations of relationships. Longitudinal data and Westen's (1993) methodology were employed to investigate questions related to (a) child-rearing antecedents of adult object relations in a nonclinical population, (b) temporal stability of adult object relations, and (c) construct validation. A multivariate effect of child-rearing variables on adult object relations was found, and significant univariate effects were nearly all in the predicted direction. Temporal stability (across 10 years) of adult object relations received tentative support. Object relations correlated positively with interpersonal functioning and physical health, but these correlations tended to be nonsignificant. A positive relationship between object relations and psychological health was not found.     

Object appearance,disappearance, and attention prioritization in real-world scenes

We examined the prioritization of abruptly appearing and disappearing objects in real-world scenes. These scene changes occurred either during a fixation (transient appearance/disappearance) or during a saccade (nontransient appearance/disappearance). Prioritization was measured by the eyes’ propensity to be directed to the region of the scene change. Object additions and deletions were fixated at rates greater than chance, suggesting that both types of scene change are cues used by the visual system to guide attention during scene exploration, although appearances were fixated twice as often as disappearances, indicating that new objects are more salient than deleted objects. New and deleted objects were prioritized sooner and more frequently if they occurred during a fixation, as compared with during a saccade, indicating an important role of the transient signal that often accompanies sudden changes in scenes. New objects were prioritized regardless of whether they appeared during a fixation or a saccade, whereas prioritization of a deleted object occurred only if (1) a transient signal was present or (2) the removal of the object revealed previously occluded objects.     

Object permanence in lemurs

Object permanence, the ability to mentally represent objects that have disappeared from view, should be advantageous to animals in their interaction with the natural world. The objective of this study was to examine whether lemurs possess object permanence. Thirteen adult subjects representing four species of diurnal lemur (Eulemur fulvus rufus, Eulemur mongoz, Lemur catta and Hapalemur griseus) were presented with seven standard Piagetian visible and invisible object displacement tests, plus one single visible test where the subject had to wait predetermined times before allowed to search, and two invisible tests where each hiding place was made visually unique. In all visible tests lemurs were able to find an object that had been in clear view before being hidden. However, when lemurs were not allowed to search for up to 25-s, performance declined with increasing time-delay. Subjects did not outperform chance on any invisible displacements regardless of whether hiding places were visually uniform or unique, therefore the upper limit of object permanence observed was Stage 5b. Lemur species in this study eat stationary foods and are not subject to stalking predators, thus Stage 5 object permanence is probably sufficient to solve most problems encountered in the wild.     

Hippocampal lesions attenuate latent inhibition and the decline of the orienting response in rats

Two experiments using rats assessed the effect of dorsal hippocampal lesions on the orienting response (OR) elicited by a discrete light and on the subsequent associability of that light. In both experiments subjects received extensive nonreinforced exposure to the light, and it was found that the decline in the OR evident in sham-operated animals was severely attenuated by hippocampal lesions. Subsequently the light was paired with condensed milk in Experiment 1, and it was found that conditioning was faster in the lesioned than in the sham-operated group. Experiment 2 used a conditioned inhibition procedure whereby the light was presented in a nonreinforced compound with a tone which, when presented alone, acted as a signal for condensed milk. Again this discrimination was mastered more rapidly by lesioned animals. Relevant control groups indicated no differences between lesioned and sham-operated animals in learning about a novel light. Thus, hippocampal lesions influence both the loss of associability of a stimulus and the decline in the OR it elicits, which, in turn, suggests that the OR acts as an index of stimulus associability.     

Object Concepts in the Chemical Senses

This paper examines the applicability of the object concept to the chemical senses, by evaluating them against a set of criteria for object‐hood. Taste and chemesthesis do not generate objects. Their parts, perceptible from birth, never combine. Orthonasal olfaction (sniffing) presents a strong case for generating objects. Odorants have many parts yet they are perceived as wholes, this process is based on learning, and there is figure‐ground segregation. While flavors are multimodal representations bound together by learning, there is no functional need for flavor objects in the mouth. Rather, food identification occurs prior to ingestion using the eye and nose, with the latter retrieving multimodal flavor objects via sniffing (e.g., sweet smelling caramel). While there are differences in object perception between vision, audition, and orthonasal olfaction, the commonalities suggest that the brain has adopted the same basic solution when faced with extracting meaning from complex stimulus arrays.     

Age,context, and spatial memory: A neuropsychological approach

Abstract

The hypothesis that a reduction in age differences in spatial location memory in the presence of distinctive cues reflects a decreased dependence on a hippocampally based memory system was tested in three experiments. In Experiments 1 and 2 the presence of distinctive cues did not reduce age differences in spatial location memory nor did these cues eliminate the significant relation between spatial location memory and a measure of hippocampal function. Distinctive cues did, however, place additional demands on processing resources and spatial visualization abilities. In Experiment 3 the relevance of prior knowledge was manipulated. With irrelevant prior knowledge there was a strong unique association between the hippocampal measure and outcome measure. With relevant prior knowledge there was no such association. the implications of these findings for understanding the role of the hippocampus in age-related decline in memory for locations are discussed.     

Improvements in Object Exploration Skills May Facilitate the Development of Object Segregation in Early Infancy

Three experiments investigated (a) the development of infants' use of features to find a boundary between 2 adjacent objects and (b) the possible connection between this ability and the development of object exploration skills. In Experiments 1 and 2, it was shown that 3 1/2-month-old infants are beginning to use object features to determine the composition of a display, interpreting a display composed of different-looking parts as 2 separate objects and a display of similar-looking parts as a single object. In Experiment 3, exploration and segregation abilities were assessed in the same infants. The results of this study were that the more actively exploring infants perceived the display used in Experiment 1 as 2 separate objects, whereas the less actively exploring infants did not. One hypothesis consistent with these findings is that infants may learn how object features can be used to find object boundaries as a result of new observations made possible by their more active exploration skills.     

Ventral scent marking in Meriones unguiculatus may contribute to thermoregulation

Three experiments were conducted with adult male Meriones unguiculatus in an attempt to demonstrate that ventral scent marking can act to transfer body heat to the object marked. Experiment 1 showed that surgical removal of the ventral gland pad reduced the amount of heat transferred by 50%, even though intact and glandless animals did not differ in the average frequency of scent marking. Experiment 2 demonstrated that the difference in heat transfer due to the presence or absence of the scent pad was not due to differential pressure applied to the substrate during marking. Experiment 3 showed that the pattern of ventral hair spread that occurs as an animal moves over an object is different between intact and glandless animals but that this difference does not account for the difference in heat transfer. It is suggested that heat transfer to the environment with ventral scent marking may increase thermoregulatory competence and also may function to volatilize sebum used in chemocommunication.     

Rorschach Object Relations of Adolescents Who Committed Homicide

We investigated the object relations of adolescents who committed homicide. A clinical sample of 55 adolescents who committed homicide did not differ from a comparison group of nonviolent delinquents on Rorschach measures of object differentiation, mutuality of autonomy, and aggressive content. However, the subgroup of adolescents who committed homicides in the context of another crime (e.g., robbery or burglary) did manifest significantly lower object relations (poorer object differentiation and more victim responses) than the subgroup of adolescents whose homicides were committed in the context of an interpersonal conflict or dispute with the victim. These findings support the need for differentiated classification of violent individuals as urged by Megargee (1970) over 20 years ago.     

The role of the hippocampus in the retrieval of a spatial location

Based on computational models of the hippocampus, it has been suggested that a possible mechanism for memory retrieval is pattern completion, wherein an autoassociative network recalls previous patterns of activity given noisy or degraded cues. However, there are few behavioral data examining pattern completion per se in the hippocampus. Here, we present a study in which rats were tested on a spatial location retrieval paradigm, each trial of which consisted of a sample and choice phase. During the sample phase, rats were trained to displace an object in one of 15 possible locations to retrieve a food reward and return to the start-box on a cheeseboard maze. The object was then removed and the same location was re-baited for the choice phase. The rats' accuracy in returning to the correct location was recorded. On test trials, visual extramaze cues, vestibular cues, or both were manipulated to assess pattern completion in normal rats. Subjects were then randomly assigned to receive a cortical control, a sham, or a dorsal and ventral hippocampal lesion and were retested on the task. Control and unoperated rats were able to perform the task when visual extramaze or vestibular cues were reliable, but not when they were manipulated. Rats with hippocampal lesions were impaired in the baseline condition, as well as during all manipulations. These results support the hypothesis that the hippocampus supports the retrieval of a spatial location, possibly through a process of pattern completion.