Play Fighting Research Articles

Play fighting between kindling-prone (fast) and kindling-resistant (slow) rats.

Differences in the play behavior of 2 strains of rats suggest that different components of play fighting can be modified independently. The development of play fighting in cross-strain pairs of familiar and unfamiliar rats was examined to determine whether interacting with a non-congruent pair-mate would alter the pattern of play typical for each strain. In both strains, changes in play fighting were observed throughout development, but partner identity appeared to influence play fighting in different ways depending on age. These data suggest that some components of play may be more impervious to changes in social environment than other components.

The effects of orbital frontal cortex damage on the modulation of defensive responses by rats in playful and nonplayful social contexts.

In a series of 3 experiments on rats, 2 hypotheses were tested: (a) that damage to the orbital frontal cortex (OFC) would alter the socially relevant context for executing defensive responses but not their performance and (b) that damage done to the OFC in early infancy would produce more deficits in social behavior than similar damage occurring in adulthood. Bilateral or unilateral OFC damage in adult males did not impair their ability to defend themselves during play fighting and when protecting their food but did impair their ability to modify the pattern of defense in response to different partners. Rats that sustained bilateral damage at 3 days of age not only had deficits in partner-related modulation of defense but also exhibited hyperactivity in their play. The findings thus supported the proposed hypotheses.

Play fighting in androgen-insensitivetfm rats: Evidence that androgen receptors are necessary for the development of adult playful attack and defense

The frequency of playful attack and the style of playful defense, are modifiable by gonadal steroids and change after puberty in male and female rats. The present study examined the play behavior exhibited by testicular feminized mutation (tfm)-affected males, who are insensitive to androgens but can bind estrogens aromatized from androgens, to determine the relative contributions of androgens and estrogens to the age-related changes in play behavior. tfm males did not exhibit a decrease in playful attack with age and were more likely to maintain the use of complete rotations, a juvenile form of playful defense, into adulthood. tfm males did however, show age related changes in the use of partial rotations and upright postures, two other forms of playful defense, that were similar to normal males. These data suggest that the development of play fighting and defense in males is dependent on both androgen- and estrogen-receptor-mediated effects.

Dominance interactions in young adult paper wasp (Polistes dominulus) foundresses: A playlike behavior?

The idea that insects play has often aroused skepticism. Nevertheless, the authors investigated the occurrence of a playlike behavior in young individuals of a paper wasp. Polistes dominulus foundresses hibernate in aggregations and found associative nests in the spring. In aggregations, wasps exhibit most of the rank-dependent behaviors that they will use in the nest 6 months later. In aggregations, precocious dominance interactions are performed with exaggerated frequencies, whereas aggression and trophallaxis are rare. Dominance behavior in aggregations is apparently useless, but it probably allows wasps to assess their dominance potential without any apparent reproductive competition. Surprisingly, these interactions may be best interpreted as play because dominance behavior in aggregations shares several features with mammalian play fighting.

Play fighting does not affect subsequent fighting success in wild meerkats

Despite more than three decades of research, the adaptive significance of play behaviour remains unknown. The practice hypothesis asserts that the primary function of play is to provide animals with the opportunity to practise and refine motor skills needed in adulthood. The apparent similarity between play fighting and serious fighting has led to the assertion that play is ‘optimally designed’ for the enhancement of combat skills. However, the practice hypothesis of play fighting has never been tested. I used data from a wild population of meerkats, Suricata suricatta (a cooperatively breeding mongoose that shows marked reproductive skew), to examine whether play experience improved an individual's subsequent fighting ability. First, meerkats showed no sex difference in frequency of play fighting (consistent with the optimal design argument, since both males and females fight to obtain the dominant breeding position in a group). Second, frequency of play fighting was not positively correlated with the subsequent likelihood of winning play fights, or the degree of improvement in play-fighting success, as would be expected if play improved fighting manoeuvres (and such manoeuvres must be the same in both play fighting and serious fighting if motor skills are to be effectively practised). Finally, individuals that ultimately won fights for a vacant dominancy did not play fight any more frequently as youngsters, or show any greater success in winning play fights, than matched same-sexed littermates that they defeated in combat.

Evolving a Playful Brain: A Levels of Control Approach

Play is rare in the Animal Kingdom, but relatively common in the larger brained vertebrate taxa. Comparisons at the level of classes, orders, and, in some cases, families, suggest that larger brained taxa are more likely to contain playful species. However, at the species level, such relationships generally disappear. In some well documented mammalian taxa, such as Rodentia, it is clear that there are species which do not play at all, some where the play is quite complex and some showing all grades in between. Comparative methods are used here to supplement proximal analyses of the content of one particular form of play, play fighting, so as to identify the neurobehavioral mechanisms that are needed in rodents to evolve complex play from simpler antecedents. At least five independent neural mechanisms are shown to be necessary to produce the most complex example of play fighting in rodents. The identification of such levels of control provides a new method for systematizing the diversity of play present in mammals. Furthermore, this approach sets the stage for re-evaluating the relationship between brain size and play. That is, the issue can be reconceptualized in terms of whether species with larger brains are more likely to have a greater number of control mechanisms. It is not that larger brained species are more likely to play, but rather, that when they do play, the content of their play is more flexible. Suitable comparative data sets are needed to test these possibilities.

Development of play fighting in kindling-prone (FAST) and kindling-resistant (SLOW) rats: how does the retention of phenotypic juvenility affect the complexity of play?

Rats selectively bred for susceptibility to amygdala kindling (FAST) have been shown to retain neural and behavioral features of the juvenile phase into adulthood. In contrast, rats selectively bred for resistance to amygdala kindling (SLOW) are neurobehaviorally more typically adult. The development of play fighting in male and female rats of both selected lines was studied. Given the apparent association of juvenility and play often noted in the literature for mammals in general, it was predicted that the FAST rats should be more playful and be more likely to retain the juvenile tactics of play that lead to more prolonged and complex patterns of social contact. As expected, FAST rats initiated more playful attacks and were more likely to defend against attacks than SLOW rats as both juveniles and adults. Unexpectedly, however, both selected lines exhibited patterns of defense that reduced the likelihood of complex and prolonged social contact. Importantly, the two selected lines did so by very different means. The FAST rats did so by avoiding contact whereas the SLOW rats did so by responding in an adult-typical manner that blocks contact. That is, the FAST rats exaggerated the changes typically occurring at puberty whereas the SLOW rats, at all ages, responded in a more adult manner. These data suggest that the different components of play fighting do not change uniformly with changes in the neurobehavioral underpinnings of juvenility.

Play fighting and real fighting: Using video playback methodology with young children

AbstractThis study develops a video playback methodology: children aged five to eight years viewed taped play fighting and real fighting bouts in which they were both participants and nonparticipants. Views of participants were also compared for immediate and delayed viewing. The methodology examines the criteria used to distinguish play fighting and real fighting; views concerning the characteristics of such episodes; and the motivations involved. The methodology was found to be feasible at this age; and useful in terms of differing views of participants and nonparticipants. There was evidence for increased insight from participants, who used more criteria to make their judgments, and more informative criteria such as knowledge of the rules of a game being played. Participant knowledge was most evident at the immediate viewings, but was partially retained one week later. Participants (more than nonparticipants) mostly described play fighting as friendly, and not involving hurt or showing off. The methodology could usefully be applied to examine further developmental changes in older children. Aggr. Behav. 30:164–173, 2004. © 2004 Wiley‐Liss, Inc.

Observers’ proficiency at identifying pretense acts based on behavioral cues

Discriminating what is pretense from what is real is a fundamental problem in development. Research has addressed the proficiency with which adults and children discriminate between play fighting and real fighting, and yet none (to our knowledge) has investigated discrimination of other kinds of pretense and real acts. In addition, little is known about what aspects of pretender behavior (as opposed to pretend content) might cue pretense interpretations. In two experiments, 8–20 s clips showing pretense and real snack behaviors were presented to adult and child participants. All participants distinguished between pretense and real behaviors at better than chance level. Furthermore, certain features (specific looking patterns and mistimed behaviors) were most prominent in the videotapes that were most often correctly identified. This provides empirical support for the suggestion that these cues, as opposed to more commonly cited cues, like smiles, might serve as important indicators of pretense for children and adults.

Experience and cortical control over the pubertal transition to rougher play fighting in rats

With the onset of puberty, play fighting in rats decreases in frequency and the tactics of attack and defense that are used are rougher. Previous studies have shown that the changes in the frequency of play and in the use of defensive tactics arise independently of social experience. Furthermore, while the former involves subcortical regulation, the latter depends on cortical mechanisms. In this study, the possible mechanisms regulating the developmental changes in the tactics of attack were examined. Two experiments were conducted using male rats. In the first study, rats reared in isolation from weaning were compared to rats reared in pairs, and were tested in the juvenile and early post-pubertal phases (30 and 60 days postnatally). In the second experiment, rats with their cortex removed shortly after birth were compared to sham-treated controls, and were tested in pairs at both the juvenile and early adult phases (30 and 90 days). Two measures of ‘roughness,’ derived from previous studies, were measured. Results showed that isolation-reared rats had the typical age-related changes in roughness of attack, whereas decorticated rats failed to show this age-related modulation, maintaining, or even exaggerating, the juvenile-typical pattern of attack. These findings suggest that social experience is not needed for this developmental change to occur, and that an intact cortex is needed to regulate this change in behavior.

Stress and the development of agonistic behavior in golden hamsters

Aggressive behavior can be studied as either offensive or defensive responses to a stimulus. The studies discussed in this review are focused on the peripubertal development of offensive aggression in male golden hamsters and its responsiveness to repeated social stress. Quantitative and qualitative changes in offensive responses were analyzed during this period. Quantitative changes in offensive responses were observed as decreased frequency of attacks. Qualitative changes were observed as changes in attack types, as animals reorient their attacks gradually from the face to the lower belly and rump. These developmental changes were altered by repeated exposure to social stress during early puberty. Daily exposure to aggressive adults during early puberty accelerated the qualitative development of offensive responses and the onset of adult-like offensive responses. In contrast, social stress had little effect on the quantitative changes associated with early puberty. However, social stress was associated with higher attack frequency during adulthood. These effects of stress during early puberty contrast with those observed with animals in late puberty. At that time, repeated exposure to aggressive adults inhibits offensive aggression. These data constitute the basis for a new theory on the development of agonistic behavior that includes the following hypotheses. First, it is hypothesized that mid-puberty is marked by a change in responsiveness to repeated social stress. As such, differences in stress responsiveness from social interactions are interpreted as a basic distinction between play fighting and adult aggression. Second, it is also hypothesized that a common neural circuitry mediates the activation of offensive responses during play fighting and adult aggressive interactions.

Problems in the study of rodent aggression

Laboratory research has produced detailed descriptions of aggression and defense patterns in the rat, mouse, and hamster, showing strong similarities, but also some differences, across these species. Research on target sites for attack, in conjunction with analyses of the situational antecedents of attack behaviors and of responsivity of these to conditions that elicit fear, has also provided a strong basis for analysis of offensive and defensive aggression strategies and for identification of combinations of these modalities such as may occur in maternal aggression. These patterns have been empirically differentiated from phenomena such as play fighting or predation and compared for laboratory rodents and their wild ancestors. An array of tasks, suitable for use with pharmacological and experimental manipulations, is available for analysis of both aggression and defense. These developments should produce a firm basis for research using animal models to analyze a broad array of aggression-related phenomena, including systematic approaches to understanding the normal antecedents and consequences of each of several differentiable types of aggressive behavior. Despite this strong empirical and analytic background, laboratory animal aggression research has been in a period of decline, spanning several decades, relative to comparable research focusing on areas such as sexual behavior or stress. Problems that may have contributed to the relative neglect of aggression research include confusion about the interpretation of different tasks for eliciting aggression; difficulties and labor intensiveness of observational measures needed for an adequate differentiation of offensive and defensive behaviors; analytic difficulties stemming from the sensitivity of offensive aggression to the inhibitory effects of fear or defensiveness; lack of a clear relationship between categories of aggressive behavior as defined in animal studies and those used in human aggression research; and the social and political difficulties undermining support for research on a topic that, when applied to humans, provides a stigmatizing label. While all of these provide some rationale for eschewing aggression research, aggression remains a serious social, economic, health, and political problem. The neglect of research in this area contributes to an ongoing failure to understand the degree of similarity across mammalian species in the antecedents, neural systems, behavioral expression, and outcomes of aggression. This failure, in turn, hinders analyses of normal and abnormal forms of aggression and of the appropriate roles of the former in society, reducing the possibility of sensitive and effective approaches to control inappropriate human aggressive behaviors.

Repeated exposure to social stress alters the development of agonistic behavior in male golden hamsters

In male golden hamsters, exposure to social stress during puberty alters aggressive behavior. Interestingly, agonistic behavior undergoes two major transitions during puberty: a decline in attack frequency and a shift from play fighting to adult-like aggression. Based on previous observations, we developed an approach for characterizing offensive responses as play fighting or adult-like. The present studies had two aims. First, we validated our approach by looking at the development of attack types during puberty. Second, we looked at the effects of repeated social stress on the development of agonistic behavior by repeatedly exposing individuals to aggressive adults during puberty. In the first phase of the study, our results point to three different developmental periods. Initially, animals engage in agonistic behavior though attacks targeted at the face and cheeks. This period lasts from Postnatal Day 20 (P-20) to P-40 (early puberty). This phase corresponding to play fighting is followed by a transitional period characterized by attacks focused on the flanks (from P-40 to P-50, mid-puberty). Afterward, animals perform adult-like aggression characterized by attacks focused on the belly and rear. Our data also show that repeated exposure to aggressive adults has two separate effects on the development of agonistic behavior. Repeated social stress accelerated the onset of adult-like agonistic responses. Furthermore, attack frequency, while decreasing during puberty, remained at a higher level in early adulthood in stressed animals. These results show that repeated exposure to social stress during puberty alters the development of agonistic behavior both qualitatively and quantitatively.

Development of “Anchoring” in the Play Fighting of Rats: Evidence for an Adaptive Age-Reversal in the Juvenile Phase

During play fighting, rats often assume a pinning configuration, where one animal stands over its supine partner. The on-top partner can stand on the ground or on its supine partner with its hind paws. When standing on the ground, the rat is more stable and is better able to respond to its partner’s actions. The frequency of this more stable pattern of standing during pinning (called anchoring) is higher following puberty than during the juvenile phase. Two hypotheses explaining this developmental change in anchoring were tested. The first hypothesis maintains that the lower level of anchoring in juvenile rats reflects an immature sensorimotor capability. The second hypothesis suggests that, since rats are more playful as juveniles, such heightened levels of play may interfere with movements otherwise used to maintain the stable anchored position at this age. Neither hypothesis was supported: infants have similar anchoring levels to postpubertal rats, and juveniles have a relatively low level of anchoring irrespective of how frequently they play fight. Therefore, the lower level of anchoring in the juvenile phase appears to be a developmental peculiarity of this age. These findings support the view that play fighting in the juvenile phase may be organized in a manner to increase the occurrence of the experiences that are developmentally beneficial in this activity.

The development of "roughness" in the play fighting of rats: a Laban Movement Analysis perspective.

With increasing age, rats, when play fighting, become rougher. In part, this change can be accounted for by the increasing likelihood of using adult-typical fighting tactics. However, even when using the same tactics, adults appear rougher than juveniles in their play. In this study, videotaped sequences of play fighting in rats from the juvenile (30 days) to the post-pubertal (70 days) period were analyzed using Laban Movement Analysis (LMA). Movement qualities called Effort Factors in LMA captured the character of some of this change. Juveniles tended to use Indulging Efforts, whereas older rats tended to use Condensing Efforts. The latter are related to performing movements that are more controlled. This greater level of control was also evident in the way older rats maintained postural support during play fights. When standing over supine partners, juveniles are more likely to stand on the partner with all four paws, reducing their postural stability, and hence ability to control their partner's movements. Older rats are more likely to place their hind paws on the ground, thus providing a firmer anchor for movements with their upper bodies and forepaws. These age-related changes in behavior were found for both males and females. The findings lend support to a growing body of evidence that play fighting in the juvenile phase of rats is not just a more frequently occurring version of that present in adults, but rather, has unique organizational properties.

Characteristics of social interaction between unfamiliar male rats (Rattus norvegicus): comparison of juvenile and adult stages

Social interaction between juvenile male rats that were unfamiliar with one another (JNI) was compared with that of adult unfamiliar animals (ANI). In their home cages, subjects were confronted with a stimulus conspecific and their agonistic behavior patterns were analyzed. It was found that behaviors that characterize "play fighting" (pouncing, submissive posture, on-top posture, etc.) were observed more in JNI than in ANI, whereas behaviors found in serious fighting (pawing, upright posture, etc.) were shown more in ANI. Analyses of the transitions between behaviors also revealed that the transitions constituting play fighting were found only in JNI. On the other hand, transitions that characterize serious fighting were shown in both JNI and ANI. These findings are discussed along with those of a previous study that observed the agonistic behavior between littermates, and the existence of some cue that signals the play-fighting situation among rats is suggested.

Sex differences in play fighting revisited: traditional and nontraditional mechanisms of sexual differentiation in rats.

In the traditional model for sexual differentiation in mammals, the female phenotype is the default condition. That is, the female-typical pattern will persist unless acted upon by hormones early in development. The frequency of play fighting in rats, as in most other mammals, is sexually differentiated, and conforms to the traditional model. Males engage in more play fighting than females, and this can be reduced to female-typical levels by neonatal castration. Furthermore, females can be induced to play fight at male-typical levels if treated with testosterone neonatally. Fractionation of play fighting into its constituent components, attack and defense, reveals that it is the frequency of attack that is sexually differentiated, not the likelihood of defense. However, in males, defensive behavior changes at puberty so that the play becomes "rougher." For males to switch to this rougher form of play fighting, they have to be androgenized perinatally. Hence, for males, this second aspect of play fighting that is sexually differentiated also follows the traditional model. In marked contrast, development of the female-typical pattern does not. Neonatal treatment of females with testosterone has no effect; at puberty, they still show the female-typical pattern. On the the other hand, ovariectomy, either at birth or at weaning, leads to females exhibiting the male-typical transition to rougher play fighting at puberty. That is, ovarian hormones appear to actively inhibit the expression of a male-typical trait in females. Play fighting, then, is a mixture of traits, with some features conforming to the traditional model and some not. For some phenotypic features, ovarian hormones appear to exert an active role in their development.

Brain system size and adult–adult play in primates: a comparative analysis of the roles of the non-visual neocortex and the amygdala

Recent studies have shown that contrary to expectation, larger-brained species within mammalian orders are not more likely to engage in play. This is true for juvenile rodents, juvenile marsupials and adult primates. Neither does the relative size of the neocortex predict the prevalence of play in species of marsupials and primates. Two methodological limitations may account for the lack of such relationships. Firstly, play may only vary systematically with specific brain areas, not overall size increases in brain tissue. Secondly, the play indices used to measure the variation in play across species may be insufficiently sensitive to the effects of changes in brain size. In this study, we attempt to deal with the first methodological problem. The adult–adult play fighting among species of primates was correlated with the relative size of the non-visual cortex and the amygdala. The statistical analyses used took into account the problems of scaling and corrected for degree of phylogenetic relatedness among the species. The size of the non-visual cortex failed to predict the prevalence of play fighting occurring in either sexual or non-sexual contexts. In contrast, the size of the amygdala significantly predicted the prevalence of sexual play, but not non-sexual play. That is, species with larger sized amygdala are more likely to engage in sexual play. These findings provide new insights into the role of different brain systems in the regulation of play behavior.

Sexual and aggressive play fighting of sibling Richardson’s ground squirrels

AbstractPlay fighting in many species of squirrels can involve sexual play and aggressive play, both of which can lead to wrestling which appears superficially similar. Such convergence can make scoring of the relative frequencies of these two types of play difficult and can lead to the mistaken conclusion that they grade into one another. In this study, both staged laboratory encounters between sibling pairs and spontaneous encounters between siblings in free‐living litters of Richardson’s ground squirrels (Spermophilus richardsonii) were videotaped. Frame‐by‐frame analyses using the Eshkol‐Wachman Movement Notation were employed to record the correlated movements of attack and defense by the partners and to reveal the body areas targeted during each play bout. Whereas sexual play was organized around access to the rump, aggressive play was organized around the shoulders. Although in most cases the defender’s tactics blocked access to the respective target, when contact did occur, it involved mounting in sexual play and nosing or biting in aggressive play. Eighty‐six percent of play fights could be unambiguously categorized as either sexual or aggressive play. Of these, the majority (˜80%) involved sexual play. The sex of the participants did not affect the frequency of aggressive play, but in sexual play, males initiated more attacks than females. Once initiated, each form of play fighting remained distinct—if a bout began as sexual play, it would end as sexual play. Furthermore, a counterattack following sexual play was significantly more likely to be sexual than aggressive, and vice versa for counterattacks following aggressive play. Therefore, all the evidence suggested that the two forms of play fighting were not intermixed in Richardson’s ground squirrels. Aggr. Behav. 27:323–337, 2001. © 2001 Wiley‐Liss, Inc.

Adult–Adult Play in Primates: Comparative Analyses of its Origin, Distribution and Evolution

AbstractComparative analyses were conducted on a data set derived from the literature so as to test several hypotheses which were developed to explain the distribution of adult–adult play fighting within the order primates. Ratings for play occurring in sexual and non‐sexual contexts were developed. Three hypotheses were evaluated: (i) that play occurring in non‐sexual social contexts is a byproduct of its use in sex; (ii) that the occurrence of play is related to its use for social assessment and manipulation, and so is more likely to be present in species with reduced familiarity between individuals; and (iii) that phylogenetic affiliation influences the likelihood that species within clades engage in play. We used independent contrasts to test the first two hypotheses, and both were significant, with the presence of play in sexual contexts accounting for 14–16% of the variance of play in non‐sexual contexts, and reduced social familiarity accounting for 30–40% of the variance in the occurrence of play in non‐sexual contexts. To test the third hypothesis, we mapped the occurrence of both types of play onto known phylogenies. The overlap was not congruent, indicating that phylogenetic relationships did not account for the distribution of play. Given that play in both sexual and non‐sexual contexts was more likely to occur in species with a social organization involving reduced frequency of contact between the sexes and other social group members, we suggest that the likely adaptive value of play fighting is as a tool for social assessment and manipulation. The possible factors that mitigate the use of play fighting for these purposes, such as the availability of other forms of communication that could serve similar functions, are discussed.