A small step for rats alters spatial behavior: rats on a bi-level arena explore each level separately.

We tested rats on a 'bi-level open-field' whose two halves were separated vertically by an 8-cm step that the rats could easily ascend/descend. We sought to determine what might be the factors that shape traveling in three-dimensional environments; what makes an environment perceived as multileveled; and how are multileveled environments explored compared to two-dimensional environments? We found that rats on the bi-level open-field traveled a greater distance on the lower level compared to the upper one. They also spent a long time at the foot of the step before ascending to the upper level. They established a home-base on one level and a local base on the other one, and explored each level separately. We could not find a particular factor that accounted for the preference for the lower level. We suggest that the momentary egocentric sensation of moving vertically, together with an overall area large enough for exploration, result in perceiving an environment as multilevel. Exploration of such environments is fragmented, and each level is explored relatively independently, as has also been shown in other studies. Regarding the unanswered question of earlier studies concerning what integrates fragmented representations, this is the first study that suggests that in rats, and perhaps also in other rodent species, such integration is achieved by means of home-base behavior, resulting in the establishment of a single comprehensive representation of the multilevel environment.

Social spatial cognition: social distance dynamics as an identifier of social interactions.

We suggest that socio-spatial behavior, which is an interaction between social and spatial cognition, can be viewed as a set of excursions that originate and end in close proximity to another individual(s). We present an extension of earlier studies that perceived spatial behavior in individual animals as a series of excursions originating from a particular location. We measured here the momentary distance between two individuals (social distance) to differentiate among eight possible types of social excursion originating in a state of proximity between excursion-participants. The defined excursion types are based on whether or not the excursion initiator also concludes the excursion, whether or not the excursion starts and ends at the same location, and the dynamics of the distance between excursion participants. We validated this approach to socio-spatial behavior as a set of excursions using it to analyze the behavior of the two sexes in rodents, of normal vs. stereotyped rats, as well as of different rodent species. Each of these groups displays a prevalent excursion type that reflects a distinct social dynamics. Our approach offers a useful and comprehensive tool for studying socio-spatial cognition, and can also be applied to distinguish among different social situations in rodents and other animals.

Rodents Prefer Going Downhill All the Way (Gravitaxis) Instead of Taking an Uphill Task.

We directly tested whether, when given the choice to ascend or descend, rodents would favor traveling downwards or upwards. The test incorporated different rodent species that dwell in different habitats and display different life and motor styles. Testing was performed in a three-dimensional Y-maze in which the basis was horizontal and, by rotating it, one arm of the maze could be pointing upwards at a certain angle and the other arm pointed downwards at the same angle. All the tested species displayed a general preference for descent, with rodents from complex habitats being less affected by inclination compared with rodents from flatlands. Unlike laboratory rats, wild species traveled greater distances along the lower compared to the upper maze arm. All the rodents initially tended to travel the entire length of the inclined maze arms, but such complete trips decreased with the increase in inclination. When introduced into the maze from top or bottom, flatland dwellers traveled mainly in the entry arm. Overall, when given the choice to ascend or descend, all the tested species displayed a preference to descend, perhaps as attraction to the ground, where they usually have their burrows.

Social spatial cognition.

Social spatial cognition refers to the interaction between self, place, and partners, with emphasis on the impact of the social environment on spatial behavior and on how individual spatial representations converge to form collective spatial behavior - i.e., common places and routes. Recent studies suggest that in addition to their mental representation (cognitive map) of the physical environment, humans and other animals also have a social cognitive map. We suggest that while social spatial cognition relies on knowledge of both the physical and the social environments, it is the latter hat predominates. This dominance is illustrated here in the modulation of spatial behavior according to dynamic social interactions, ranging from group formation to an attenuation of drug-induced stereotypy through the mere presence of a normal subject. Consequently we suggest that the numerous studies on the biobehavioral controlling mechanisms of spatial behavior (i.e. - the hippocampal formation, animal models for mental disorders) should also consider the social environment rather than solely focusing on the spatial behavior of lone animals.

Social interaction modulates the intensity of compulsive checking in a rat model of obsessive-compulsive disorder (OCD).

Here we present an empirical study that provides a basis for understanding the impact of the social environment on individuals with mental disorders. Rats treated chronically with the dopamine-agonist quinpirole offer a solid animal model for compulsive behavior that has been comprehensively evaluated and validated in numerous studies. Moreover, the method of behavioral analysis used in the quinpirole rat model has been similarly applied to the analysis of compulsive rituals in OCD patients, revealing similarities to the structure of compulsions in the quinpirole-sensitized rats. Here, we examined how compulsive checking by quinpirole-sensitized rats was modulated by the presence of a partner that was also treated with quinpirole or a partner that was treated with saline, compared to the typical expression of compulsive checking shown by rats tested alone. Our results demonstrate that the presence of a partner does indeed modulate the performance of checking behavior. Specifically, the vigor of compulsive checking was attenuated in the presence of a saline-treated partner, and augmented in the presence of a quinpirole-treated partner. This finding provides compelling evidence that social interactions modulate the expression of compulsive checking in the quinpirole rat model of OCD. This uncovering of the effectiveness of social modulation, indicates the quinpirole preparation as a paradigm for investigating the mechanisms by which the social environment modulates the development and expression of OCD. More generally, it presents a paradigm for the study of the influence of drug effects as a function of social interaction.

The hierarchy of food, sociality, and experience in spatial decision-making by food-deprived rats.

We examined whether a hierarchy existed among attraction to (i) food; (ii) social partner(s); and (iii) familiar feeding location in spatial decision-making in rats. To determine this, lone food-deprived rats were trained to collect baits from 16 salient equispaced objects arranged in a grid layout. Some rats were trained with only the eight objects on the left baited; other rats with only the eight objects on the right baited. After training, dyads of one left-trained and one right-trained rats were tested, with the eight baits now divided into four on the left and four on the right sides of the arena. Rats were free either to go to the familiar objects that had been baited in the lone training trials, regardless of whether these objects were now actually baited; or, alternatively, they could go to baited objects regardless of their side and of the rats' past experience. Rats could also forage individually or together regardless of their past experience or actual bait location. We found that the rats primarily displayed attraction to baits, regardless of their location; followed by a preference to travel together; and then by a significant combined attraction to visit together baited objects (whether familiar or not). Accordingly, attraction to food had the prime influence, sociality the second, and familiarity with the environment the least, in establishing spatial foraging decisions.

Rats do not eat alone in public: Food-deprived rats socialize rather than competing for baits.

Limited resources result in competition among social animals. Nevertheless, social animals also have innate preferences for cooperative behavior. In the present study, 12 dyads of food-deprived rats were tested in four successive trials, and then re-tested as eight triads of food-deprived rats that were unfamiliar to each other. We found that the food-deprived dyads or triads of rats did not compete for the food available to them at regular spatially-marked locations that they had previously learnt. Rather, these rats traveled together to collect the baits. One rat, or two rats in some triads, lead (ran ahead) to collect most of the baits, but "leaders" differed across trials so that, on average, each rat ultimately collected similar amounts of baits. Regardless of which rat collected the baits, the rats traveled together with no substantial difference among them in terms of their total activity. We suggest that rats, which are a social species that has been found to display reciprocity, have evolved to travel and forage together and to share limited resources. Consequently, they displayed a sort of 'peace economy' that on average resulted in equal access to the baits across trials. For social animals, this type of dynamics is more relaxed, tolerant, and effective in the management of conflicts. Rather than competing for the limited available food, the food-deprived rats socialized and coexisted peacefully.

Traveling Companions Add Complexity and Hinder Performance in the Spatial Behavior of Rats.

We sought to uncover the impact of the social environment on the spatial behavior of rats. Food-deprived rats were trained in a spatial task of collecting food items from 16 equispaced objects. Following training, they were tested, first alone and then with a similarly-trained cage-mate. It was found that the presence of another rat substantially altered the rats' spatial behavior. Lone rats collected the food items faster while traveling a shorter distance, reflecting a higher efficiency of task completion. When accompanied by a partner, however, the rats traveled together, visiting the same set of objects in each trip with one of them leading. Whether alone or with a partner, rats continued to revisit the same objects; however, more such revisits occurred with a partner. We argue that revisiting objects is not necessarily an error, since returning to past places is an important aspect of rats' natural behavior. Revisiting an object following food depletion implies that searching for food was not the main driving force in the rats' spatial behavior. Specifically, despite food deprivation, rats were more attentive to one another than to the food. This could be adaptive, since foraging and feeding in groups is a way of poison avoidance in wild rats. Finally, the addition of a social component added complexity to the environment since the rats organized their spatial behavior in reference to one another in addition to their organization in the physical surrounding. Consequently, when tested with a partner, spatial behavior was less structured, less predictable and more chaotic.