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Several studies on rats and hamsters, across multiple laboratories, have shown that limiting play in the juvenile period leads to adults that have physiological and anatomical changes in the medial prefrontal cortex (mPFC) and reduced socio-cognitive skills. Peers raised with playful peers have better socio-cognitive skills than animals raised with adult partners. Using Long Evans hooded rats - a commonly used domesticated strain - this relationship has been replicated multiple times. However, when the same paradigm was used with laboratory-reared wild rats, no differences were found between rats reared with peers and ones reared with adults. It has been shown that the key play-generated experiences involved are those related to actively wrestling with a partner and turn taking (as measured by role reversals), which give both partners opportunity to gain the advantage during play fighting. In the present study, we tested the hypothesis that wild rat adults provide juveniles more such experiences than do adult Long Evans rats. The asymmetry in the play interactions in adult-juveniles pairs was compared between the two strains. As predicted, wild rat adults initiated more play with the juveniles, wrestled more and provided more opportunities for role reversals. The findings thus support the hypotheses for the observed strain differences in the effects of rearing condition on the mPFC.

Play fighting in many species involves partners competing to bite one another while avoiding being bitten. Species can differ in the body targets that are bitten and the tactics used to attack and defend those targets. However, even closely related species that attack and defend the same body target using the same tactics can differ markedly in how much the competitiveness of such interactions is mitigated by cooperation. A degree of cooperation is necessary to ensure that some turn-taking between the roles of attacker and defender occurs, as this is critical in preventing play fighting from escalating into serious fighting. In the present study, the dyadic play fighting of captive troops of 4 closely related species of Old World monkeys, 2 each from 2 genera of Papio and Mandrillus, was analyzed. All 4 species have a comparable social organization, are large bodied with considerable sexual dimorphism, and are mostly terrestrial. In all species, the target of biting is the same – the area encompassing the upper arm, shoulder, and side of the neck – and they have the same tactics of attack and defense. However, the Papio species exhibit more cooperation in their play than do the Mandrillus species, with the former using tactics that make biting easier to attain and that facilitate close bodily contact. It is possible that species differences in how rigidly dominance relationships are maintained are expressed in the play of juveniles by altering the balance between competition and cooperation.

Social interactions are often analyzed by scoring segments of predefined behavior and then statistically assessing numerical and sequential patterns to identify the structure of the encounters. However, this approach can miss the dynamics of the animals' relationship over the course of the encounter, one that often involves invariant bonds, say a nose-to-nose orientation, with many different movements performed by both partners acting to counteract each other's attempts to break or maintain the relationship. Moreover, these invariant bonds can switch from one configuration to another during an interaction, leading from one stable configuration to another. It is this stepwise sequence of configurational stabilities that lead to functional outcomes, such as mating, aggression, or predation. By focusing on the sequence of invariant relational configurations, the deep structure of interactions can be discerned. This deep structure can then be used to differentiate between compensatory movements, no matter how seemingly stereotyped they may appear, from movement patterns which are restricted to a particular form when more than one option is available. A dynamic perspective requires suitable tools for analysis, and such tools are highlighted as needed in describing particular interactions. [ABSTRACT FROM AUTHOR]

Studies of rats and some primates show that rough-and-tumble play among juveniles improves social competence, cognition, and emotional regulation later in life. Most critically, such play makes animals better able to respond to unexpected situations. But not all animals engage in play, and not all animals that play appear to gain these benefits. Using a model developed by Burghardt (2005), the authors argue that there are enabling conditions--such as how behavior systems develop and the presence of surplus resources--that make play-like behavior possible. Once such behavior emerges, other enabling conditions help transform it into more exaggerated patterns of play that can be co-opted for various functions. For species living in complex social systems with an extended juvenility, play has become a tool to refine the control that the prefrontal cortex has over other neural circuits. Such control permits these animals to have more nuanced responses to a variety of situations. In short, the juvenile experience of play refines the brain to be more adaptable later in life.

Rough-and-tumble play, or play fighting, is common in the young of many mammals. Research on play fighting among rats shows that there are many levels of neural control over this behavior: subcortical mechanisms mediate the motivation and behavior of such play, and the cortex provides mechanisms by which the play changes with age and context. The cortical mechanisms help to explain the advantages playing offers the brain. The cortically induced modulations of the content of play with age ensure that exposure to particular kinds of experiences are enhanced during the critical juvenile period. These experiences, in turn, modify the development of other areas of the cortex. Such cortical changes appear to mediate the effects of play on the refinement of social skills. As a result, rats that play as juveniles are more socially competent as adults. This work was supported by the Natural Sciences and Engineering Research Council of Canada and the Alberta Heritage Foundation for Medical Research.

Macaques are the most geographically widespread and behaviorally diverse primate genus, and although macaque species share the same, basic social structure, they display broad inter specificvariation in patterns of adult social behavior. Based on these patterns, macaque species have been arranged along a 4-grade scale for social style. At one end of the scale, there are grade 1 species (e.g., Japanese macaques) that have highly hierarchical and despotic social systems, and at the other end, grade 4 species (e.g., Tonkean macaques) that have more relaxed and egalitarian social systems. We predicted that a species from the more despotic end of the spectrum should have more competitive play fights and that a species from the egalitarian end, more cooperative ones. A detailed analysis of videotaped sequences of juvenile play fighting in Tonkean and Japanese macaques was used to characterize the targets and tactics of attack and defense. Even though the two species have a similar behavioral repertoire, there are significant differences in how that repertoire is used and these differences are consistent with one species having more competitive interactions than the other. Contrasting multi-animal play fights versus pairs showed that the more cooperative style of the Tonkean macaques is further exaggerated. The results suggest that differences in styles of attack anddefense in play fighting may be influenced by differences in the species’ social systems.

In rats (Rattus norvegicus), juvenile males engage in more play fighting (a male-typical behavior) than do juvenile females, and this difference is based o perinatal influences of androgens. We show that there are qualitative and quantitative differences between the sexes in the type of defensive responses and their manner of execution. In defensive responses rats try to avoid having their napes contacted by the partner's snout. The sex differences arise from females' greater response distance; that is, females responded to an approach when the partner's snout was further from the nape. This permits females to use different defensive responses and to use them more successfully. This greater response distance is defeminized by the neonatal administration of testosterone propionate. Our findings suggest that play fighting in rats has both male- and female-typical features and that these are, at least in part, influenced perinatally by androgens.

Neonatal testosterone supplementation does not influence adult dominance behavior among male rats, but juvenile play fighting does increase with neonatal hormonal treatment. An analysis of play fighting between pairs of male sibling rats was made in which one sibling in each pair had been injected with testosterone propionate (TP) or oil vehicle and one sibling was untreated. Juvenile TP-treated rats started more attacks, though defense responses remained similar between treated and untreated rats. Adult dominance was not influenced by neonatal testosterone treatment.

The subordinate sibling in a pair of adult male rats is pinned down more often in play attacks because he originates more playful attacks and defends himself in a more juvenile way than his dominant sibling does. A study of 26 male Long Evans hooded rats from five litters analyzed the development of dominance-subordinance relationships. Dominant partners use adult defensive techniques, while subordinates revert to juvenile patterns of turning supine when attacked at the nape.

Studies of intraspecific fighting in two species of voles show that prairie vole resident males attacked the head instead of the rear if the defender turned to face the attacker, but montane vole resident males continued to attack the defender's rear. Videorecorded tapes of defensive and offensive behavior of both vole species were analyzed in depth. The study also revealed that defensive prairie voles retreated after each ineffective defense. Montane voles, however, faced their attackers tenaciously.

Experiments were conducted to study the use of supine behavior as a defensive ploy in male house mice Mus Domesticus. Results indicated that this maneuver is used by mice to prevent attacking opponent from biting them in the region of the lower dorsum. Supine behavior is, therefore, not a submissive tactic but is a dynamic defensive behavior to protect specific areas of the body. The mice do not remain in this position for long, but immediately return to prone position and flee.

A study is made of the fighting/defending tactics and the specific target of attack of the northern grasshopper mice onychomys leucogaster to determine patterns or contextual rules which govern the use of fighting tactics. Results show that the grasshopper mice, which is a very aggressive species, favor the bilateral attack most in fighting/defending an upright defensive posture taken by opponents.