Geometry learning while navigating: The importance of task difficulty and sex differences.

Cheng (1986) trained male rats to search for food in a rectangular arena that also contained distinctive visual patterns. He found that the rats used mainly the geometric framework of the box itself to find the food and claimed that geometrical information is processed in a specialized module, which is independent of feature information. The aim of the present set of experiments was to check if the previous results with male rats and an appetitive task could be extended to an aversive task while using both male and female rats and three-dimensional landmarks. In Experiments 1 and 2, rats were trained in a rectangular-shaped pool to find a hidden platform that had a location defined in terms of two sources of information-landmarks of different salience (less salient in Experiment 1, more salient in Experiment 2) outside the pool and a particular corner of the pool. The results showed that both males and females used mainly the particular corner of the pool, supporting Cheng's suggestion. In addition, in the two experiments, what the rats learned with respect to the landmarks was negligible. Experiment 3 used a more difficult triangular pool in addition to the rectangular pool, in the absence of landmarks. The results revealed sex differences in the triangular pool but not in the easier rectangular pool. These results suggest that task difficulty is a factor when it comes to finding sex differences in rats in spatial tasks. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Generalisation decrement and not overshadowing by associative competition among pairs of landmarks in a navigation task with humans.

In three experiments, a virtual preparation for humans of the Morris water task (VMWT) was used. Experiment 1 established that four landmarks were of similar salience. Then, in Experiments 2 and 3, participants were trained to locate a hidden platform in the presence or either two or four of the previous landmarks. In Experiment 2, one pair of groups was trained with four visual landmarks spaced at equal intervals around the edge of the pool, while a second pair was trained with two landmarks only, either relatively close to or far from the hidden platform. After training, a reciprocal overshadowing effect was found: on a test without the platform with two landmarks only (either close to or far from the platform position), the participants trained with four landmarks spent less time in the platform quadrant than those trained with only two. Finally, Experiment 3 showed that at least participants trained with two landmarks relatively close to the platform and then tested with four also performed worse on test than those trained and tested with two close landmarks only. This result suggests that generalisation decrement, rather than associative competition, could provide a sufficient explanation for the overshadowing observed in Experiment 2 in the proximal groups. The present set of experiments extend, although only partially, the generalisation decrement results documented in rats to human participants.

Anti-oxidative effects produced by environmental enrichment in the hippocampus and cerebral cortex of male and female rats.

Both physical and intellectual activity may reduce the incidence of neurodegenerative disorders. There is evidence that environmental enrichment (EE) can induce profound behavioral, neurochemical and neuroanatomical changes, thus producing lasting improvements in memory and learning tasks. In this study we evaluated the anti-oxidative effects produced by EE in the hippocampus and the cerebral cortex of male and female rats. The animals had been reared in either EE or control conditions. The parameters studied were: thiobarbituric acid reactive substances (TBARS), protein oxidation, total radical antioxidant parameter, catalase, superoxide dismutase and superoxide anion activity. The results showed that our EE protocol reduced markers of oxidative stress in the hippocampus and in the cerebral cortex. Overall, the measures taken in the two cerebral regions revealed that EE rats showed higher values for antioxidant measures and lower values for oxidative stress parameters than control animals. More importantly, a consistent sex difference was found, indicating that in female rats the hippocampus and cerebral cortex are plastic brain regions receptive to external stimulation such as EE. Although EE males have higher levels for antioxidant capacity, catalase and SOD, it is likely that females do not need to activate all the antioxidant defenses since they have a greater capacity to assimilate external stimuli. This is suggested by the similarity of protein oxidation and TBARS levels in hippocampus in both sexes, and the even lower levels of protein oxidation and superoxide anion activity in the cerebral cortex in EE females.

Navigation with two landmarks in rats (Rattus norvegicus): the role of landmark salience.

In two experiments, male and female rats were trained in a Morris pool in the presence of 1 (Experiment 1) or 2 (Experiment 2) landmarks, which were placed relatively close in relation to a hidden platform. Experiment 1 established the relative salience of 3 landmarks. Two of them revealed a similar salience, and smaller than a third one, the most salient landmark, both in training and on a test trial without the platform. Then in Experiment 2 rats were extensively trained to find a hidden platform in the presence of a configuration formed by 2 landmarks and the effects of varying the salience of one of the landmarks were studied. Subsequent test trials without the platform revealed that finding the platform was controlled by different strategies and that the rats were taking advantage of this redundancy depending on the nature of the test trials. Surprisingly, in Experiment 2 a clear sex difference was found on escape trials only, with males reaching the platform faster than females.

Generalization decrement and not overshadowing by associative competition among pairs of landmarks in a navigation task.

When they are trained in a Morris water maze to find a hidden platform, whose location is defined by a number of equally spaced visual landmarks round the circumference of the pool, rats are equally able to find the platform when tested with any two of the landmarks (Prados, & Trobalon, 1998; Rodrigo, Chamizo, McLaren, & Mackintosh, 1997). This suggests that none of the landmarks was completely overshadowed by any of the others. In Experiment 1 one pair of groups was trained with four equally salient visual landmarks spaced at equal intervals around the edge of the pool, while a second pair was trained with two landmarks only, either relatively close to or far from the hidden platform. After extensive training, both male and female rats showed a reciprocal overshadowing effect: on a test with two landmarks only (either close to or far from the platform), rats trained with four landmarks spent less time in the platform quadrant than those trained with only two. Experiment 2 showed that animals trained with two landmarks and then tested with four also performed worse on test than those trained and tested with two landmarks only. This suggests that generalization decrement, rather than associative competition, provides a sufficient explanation for the overshadowing observed in Experiment 1. Experiment 3 provided a within-experiment replication of the results of Experiments 1 and 2. Finally, Experiment 4 showed that rats trained with a configuration of two landmarks learn their identity.

Order effects after blocked preexposure to two compound flavors.

In the first three experiments two groups of rats received prolonged blocked preexposure to AX-BX or to BX-AX. Experiment 1 showed that conditioning of AX after preexposure resulted in less generalization to BX in the AX-BX group than in the BX-AX group. Experiments 2 and 3 constituted, respectively, retardation and summation tests of the inhibitory properties acquired by B after preexposure and conditioning of A. Excitatory conditioning of B was retarded in the AX-BX group (Experiment 2) and only in this group B was able to alleviate the aversion conditioned to a new stimulus (Experiment 3). These results are explained as a consequence of the formation, in the AX-BX group, of inhibitory associations directed from B to A. A fourth experiment provided evidence that the A↔X association was preserved until the end of the preexposure phase in this group, which is a requisite for the formation of these inhibitory associations.

The conditioned stimulus elicits taste aversion but not sickness behavior in conditioned mice.

OBJECTIVES: This article extends previous reports on (i) elicitation of taste aversion after pairing a flavored beverage (saccharin solution) with a disease-provoking microbial product (lipopolysaccharide, LPS, or polyinosinic:polycytidylic acid, poly I:C); (ii) elicitation of sickness behavior (assessed as diminished ingestion of water and food) by the conditioned stimulus, and (iii) development of tolerance to those microbial products. METHODS: Mice of the CD1 strain were conditioned by pairing ingestion of 0.15% saccharin solution with injection of LPS (100 mug/mouse) or poly I:C (6 mg/kg). A few days later, some mice were offered saccharin solution and were injected with saline, whereas other mice were offered saccharin solution and were injected with the microbial product. RESULTS: Regardless of the nature of the unconditioned stimulus (LPS or poly I:C), (i) taste aversion to saccharin ensued, (ii) tolerance ensued to sickness elicitation by a second administration of the microbial component, and (iii) saccharin taste did not evoke sickness. CONCLUSIONS: Symptoms of infectious sickness in the absence of infection are hardly explained by exposure to the conditioned stimulus.

Is contextual-potentiated eating dependent on caloric density of food?

Se puso a prueba en un experimento con ratas si un contexto específico podría provocar la conducta de comer como resultado del condicionamiento Pavloviano, y si este efecto dependía de la densidad calórica del alimento. Treinta y dos ratas privadas de comida experimentaron dos contextos. Los animales tenían acceso al alimento en el contexto A, pero nunca encontraron alimento en el contexto B. La mitad delos animales recibió un alimento de alta densidad calórica (grupos HD) mientras que la otra mitad recibió un alimento de baja densidad calórica (grupos LD) durante las sesiones de condicionamiento. Posteriormente, la mitad de los animales en cada tipo de alimento se puso a prueba en el contexto A y la otra mitad en el contexto B. Los resultados mostraron un efecto de condicionamiento contextual solamente en los grupos HD. Estos resultados sugieren la importancia del condicionamiento del contexto y de la densidad calórica del alimento en la conducta de comer. Se discuten las implicaciones que estos hallazgos pueden tener en la etiología de la conducta de atracón (AU)

One experiment tested whether a specific context could elicit eating in rats as a result of Pavlovian conditioning and whether this effect depended on the caloric density of food. Thirty two deprived rats experienced two contexts. They had access to food in context A, but no food was available in context B. During conditioning, half of the animals received high density caloric food (HD groups) whereas the other half, low density caloric food (LD groups). Then, half of the rats in each type of food group was tested in context A and the other half in context B. The results demonstrated an effect of context conditioning only in HD groups. These findings suggest the relevance of both contextual conditioning and caloric density of food I neating behaviour. Implications for the a etiology of binge eating will be discussed (AU)

Is contextual-potentiated eating dependent on caloric density of food?

One experiment tested whether a specific context could elicit eating in rats as a result of Pavlovian conditioning and whether this effect depended on the caloric density of food. Thirty two deprived rats experienced two contexts. They had access to food in context A, but no food was available in context B. During conditioning, half of the animals received high density caloric food (HD groups) whereas the other half, low density caloric food(LD groups). Then, half of the rats in each type of food group was tested in context A and the other half in context B. The results demonstrated an effect of context conditioning only in HD groups. These findings suggest the relevance of both contextual conditioning and caloric density of food in eating behaviour. Implications for the aetiology of binge eating will be discussed (AU)

Se puso a prueba en un experimento con ratas si un contexto específico podría provocar la conducta de comer como resultado del condicionamiento Pavloviano, y si este efecto dependía de la densidad calórica del alimento. Treinta y dos ratas privadas de comida experimentaron dos contextos. Los animales tenían acceso al alimento en el contexto A, pero nunca encontraron alimento en el contexto B. La mitad delos animales recibió un alimento de alta densidad calórica (grupos HD) mientras que la otra mitad recibió un alimento de baja densidad calórica (grupos LD) durante las sesiones de condicionamiento. Posteriormente, la mitad de los animales en cada tipo de alimento se puso a prueba en el contexto A y la otra mitad en el contexto B. Los resultados mostraron un efecto de condicionamiento contextual solamente en los grupos HD. Estos resultados sugieren la importancia del condicionamiento del contexto y de la densidad calórica del alimento en la conducta de comer. Se discuten las implicaciones que estos hallazgos pueden tener en la etiología de la conducta de atracón (AU)

Taste-aversion conditioning, but not immunosuppression conditioning, occurs under partial water deprivation.

The authors investigated whether conditioned taste aversion and immunosuppression took place when water was available during conditioning and test protocols. The authors elicited taste-aversion conditioning and immunosuppression in outbred CD1-strain mice by pairing a conditioned stimulus (sucrose or saccharin solution) with an unconditioned stimulus (cyclophosphamide) that causes gastrointestinal upset and is immunosuppressive. The authors introduced a new conditioning protocol: 5 pairings of a saccharin solution with a low-dose injection of cyclophosphamide. Under these conditions, the authors generated conditioned aversion to saccharin but did not generate conditioned decrease of the antibody response. The authors conclude that taste-aversion conditioning, but not immunosuppression conditioning, occurred under partial water deprivation.