Feminine dimension in the play fighting of rats (Rattus norvegicus) and its defeminization neonatally by androgens.

In rats, juvenile males engage in more play fighting (a male-typical behavior) than do juvenile females, and this difference is based on perinatal influences of androgens. The authors 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 their 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. 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tactile stimulation during development attenuates amphetamine sensitization and structurally reorganizes prefrontal cortex and striatum in a sex-dependent manner.

This study investigated the effect of postnatal tactile stimulation (TS) on juvenile behavior, adult amphetamine (AMPH) sensitization, and the interaction of TS and AMPH on prefrontal cortical (PFC) thickness and striatum size. Pups received TS by stroking daily with a feather duster from birth till weaning and were tested, as juveniles, in behavioral tasks including open field locomotion, elevated maze, novel object recognition, and play fighting behavior. Development and persistence of drug-induced behavioral sensitization was tested by chronic AMPH administration and challenge, respectively. PFC thickness and striatum size were assessed from serial brain sections. The findings showed that TS rats spent less time with novel objects on first exposure but open field locomotion and elevated plus maze tasks were not affected substantially. TS reduced the frequency of play fighting and enhanced evasion in response to a playful attack, but only in males. The probability of complete rotation defense, leading to a supine posture during play, was reduced in both sexes. AMPH administration resulted in gradual increase in behavioral sensitization that persisted at least for 2 weeks. However, TS rats exhibited attenuated AMPH sensitization compared to sex-matched controls. Neuroanatomically, AMPH reduced the PFC thickness in control females but enlarged the posterior striatum in control males. TS experience blocked these effects. In summary, TS during development modulated the response to novel objects and altered social behaviors and attenuated AMPH-induced behavioral sensitization by preventing drug-induced structural alteration in the PFC and the striatum, brain regions implicated in drug abuse. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The modulation of play fighting in rats: Role of the motor cortex.

The cortex is not necessary for rats to engage in play fighting, but it is necessary for them to modify their pattern of play fighting in different contexts. Two experiments were conducted to determine the role of the motor cortex (MC). Rats with bilateral ablations of the MC performed on Postnatal Day 10 failed to show the normally present age-related modulation in defense but were able to modulate defense with different social partners. This latter finding was confirmed in rats given ablations as adults, in which responses to social status could be monitored before and after brain damage. It appears that different forms of cortical modulation of play fighting involve different cortical circuits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adult play fighting and potential role of tail signals in ringtailed lemurs (Lemur catta).

Adult strepsirrhines have been completely neglected in the study of animal play. I focused on adult play fighting and the role of tail-play as a signal in ringtailed lemurs (Lemur catta). Tail-play is performed during play fighting, when lemurs anoint or, more rarely, wave their tails toward the playmate. During the prereproductive period, male and female lemurs engaged in play fighting with comparable frequencies, as was expected to occur in monomorphic species such as L. catta. The dyads showing low aggression rates engaged most frequently in play fighting, and polyadic play was frequently performed. Signals seem to be important in avoiding escalation to real aggression, especially when the playfulness of performers can be misunderstood by recipients. Tail-play was most frequent (a) in the dyads with low grooming rates (low familiarity degree) and (b) during the most risky play sessions (polyadic ones). Thus, tail-play can be considered as a useful tool for play communication in ringtailed lemurs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Escalation of feline predation along a gradient from avoidance through "play" to killing.

In this article, we show that feline predation involves a continuous gradient of activation between defense and attack and that predatory "play" results from an interaction of the two. Benzodiazepines (oxazepam, diazepam) escalated attack toward killing, so that cats that had avoided mice prior to the drug now played with them, cats that had originally played now killed, and cats that killed mice now did so with less preliminary contact. In such shifts, no sharp demarcation between play and predation was evident. Lateral hypothalamic lesions disrupted the escalation of attack. During recovery, attack was escalated once again along the gradient toward killing, but in the absence of both defense and play. A similar result was obtained in intact killers and nonkillers by the application of mild tailpinch. These results suggest that play with prey is a misnomer for predatory behavior that fails to escalate along the gradient between defense and attack. Movement notation analysis revealed that playful movements are adaptive in that they protect the cat from injury. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral and developmental consequences of early rearing experience for captive giant pandas (Ailuropoda melanoleuca).

Mother-reared (MR) and peer-reared (PR) captive giant panda (Ailuropoda melanoleuca) cubs were compared to evaluate the effects of early removal from mother on behavioral development. Males and females and twins and singletons were compared to assess the effects of social setting on behavioral development. Subjects included 2 PR females, 3 MR females, 3 MR males, and 3 mothers. MR cubs spent more time manipulating bamboo and fell more often than PR cubs. PR cubs spent more time inactive. Male cubs directed more playful behavior at their mothers. Twins spent more time play fighting with their mothers than with their siblings. The results suggest that peer-rearing does not provide young pandas with the same level of social stimulation as mother-rearing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physical activity play: the nature and function of a neglected aspect of playing

In this review, we consider the nature and possible developmental functions of physical activity play, defined as a playful context combined with a dimension of physical vigor. We distinguish 3 kinds of physical activity play, with consecutive age peaks: rhythmic stereotypies peaking in infancy, exercise play peaking during the preschool years, and rough-and-tumble play peaking in middle childhood. Gender differences (greater prevalence in males) characterize the latter 2 forms. Function is considered in terms of beneficial immediate and deferred consequences in physical, cognitive, and social domains. Whereas most theories assume that children's play has deferred benefits, we suggest that forms of physical activity play serve primarily immediate developmental functions. Rhythmic stereotypies in infancy are hypothesized to improve control of specific motor patterns. Exercise play is hypothesized to function primarily for strength and endurance training; less clear evidence exists for possible benefits for fat reduction and thermoregulation. In addition, there may be cognitive benefits of exercise play that we hypothesize to be largely incidental to its playful or physical nature. Rough-and-tumble play has a distinctive social component; we hypothesize that it serves primarily dominance functions; evidence for benefits to fighting skills or to emotional coding are more equivocal. Further research is indicated, given the potentially important implications for children's education, health, and development.     

To whom the play signal is directed: A study of headshaking in black-handed spider monkeys (Ateles geoffroyi).

Spider monkeys shake their heads so as to facilitate amicable social contact. This occurs frequently during vigorous play fighting, and so is common during the juvenile period. Occasionally, juvenile spider monkeys use headshakes during nonsocial locomotor play. In this study, head shaking in early infancy and in adulthood was studied in a captive troop of spider monkeys, with a total of 8 infants studied from shortly after birth to just before weaning. Three hypotheses to account for these nonsocial headshakes were tested. The play as the experience of the unexpected hypothesis was found wanting because nonsocial headshakes were most common in early infancy, before the onset of the juvenile peak in play. The immature misdirection of signals hypothesis was also found wanting because the headshakes were correctly directed at other monkeys, but not at inanimate objects that were grabbed and mouthed. Both also failed to predict the occurrence of the observed nonsocial headshakes in adults. The hypothesis best supported by the data is that, under some situations, headshakes are self-directed to promote action when confronting contexts of uncertainty. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effects of neonatal handling on play behavior and fear towards a predator odor in juvenile rats (rattus norvegicus).

The effects of brief daily separation, also known as "handling," during the first 2 weeks of life on play behavior and fearfulness toward a predatory odor were assessed in juvenile rats. Handled rats were more playful than nonhandled control rats, and while handling had no effect on the direct response of these rats toward a predatory odor, handled rats did not exhibit a conditioned suppression of play when tested later in the same context where they had been exposed to the predatory odor. Handled rats were still wary of the environment in that they continued to show a heightened level of risk assessment behavior. These data suggest that early postnatal experiences may play a significant role in determining how an animal deals with predatory threats later in life. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Same-sex and opposite-sex best friend interactions among high school juniors and seniors

Eighteen adolescents were videotaped during same-sex and opposite-sex interactions in the eleventh and twelfth grades. In both grades, females felt more comfortable during same-sex interactions than during opposite-sex interactions, and they rated their same-sex partners more positively than did males. Females in both grades and males in eleventh grade showed more peer intimacy than did males in twelfth grade. Eleventh-grade females showed the most playful behaviors (the most engaged state). More synchrony (matching of behavior) was found for the animated state in the twelfth grade as compared with the eleventh grade.     

The role of the medial prefrontal cortex in the play fighting of rats.

Although decorticated rats are able to engage in play, their play is abnormal in three ways. First, decorticates do not display the normal, age-related shifts in defensive strategies during development. Second, decorticates do not modify their defensive tactics in response to the social identity of their partners. Third, decorticates display a global shift in defensive tactics from more complex to less complex strategies. It has been shown that lesions of the motor cortex (MC) selectively produce the abnormal developmental effects on play, and that lesions of the orbitofrontal cortex (OFC) selectively produce the deficits in behavioral discrimination between social partners. In the current set of experiments, we demonstrate that lesions of the medial prefrontal cortex (mPFC) produce the shift from more complex to less complex defensive tactics, while leaving intact the age-related and partner-related modulation of defensive strategies. Thus, we have evidence for a triple dissociation of function between the MC, the OFC, and the mPFC with respect to social play behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bubble ring play of bottlenose dolphins (Tursiops truncatus): Implications for cognition.

Research on the cognitive capacities of dolphins and other cetaceans (whales and porpoises) has importance for the study of comparative cognition, particularly with other large-brained social mammals, such as primates. One of the areas in which cetaceans can be compared with primates is that of object manipulation and physical causality, for which there is an abundant body of literature in primates. The authors supplemented qualitative observations with statistical methods to examine playful bouts of underwater bubble ring production and manipulation in 4 juvenile male captive bottlenose dolphins (Tursiops truncatus). The results are consistent with the hypothesis that dolphins monitor the quality of their bubble rings and anticipate their actions during bubble ring play. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sibling effects on the behavior of infant mouse litters (Mus domesticus).

We investigated whether the number of same- or other-sex littermates had a graded effect on the occurrence of early solitary play and social play by mouse (Mus domesticus) family units. Sixty litters, reduced at birth to 5 different sex ratios (6 males, 5 males and 1 female, 3 males and 3 females, 1 male and 5 females, and 6 females) were scored in 15-min sessions on postnatal Days 18 and 21. An increasing trend with age was found for run, pounce, popcorn, self-groom, and explore episodes. Type of family unit influenced the occurrence of specific social interactions: One male-5 female and 6 female litters showed more social play than similar male litters. Litters with a balanced sex ratio showed higher exploration than isosexual litters. The results extend previous reports of both social and solitary play in developing laboratory mice and, in contrast with rat data, indicate a marked female primacy in playful social behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of cooperative territoriality in juvenile lions

African lions, Panthera leo, engage in many cooperative activities including hunting, care of young, and group territoriality, but the contribution of juvenile lions to these activities has never been documented. Here we present experimental evidence that juvenile lionesses make a gradual transition to group-territorial defence between weaning (8 months) and sexual maturity (42 months). When challenged by simulated intruders played from a loud-speaker, juvenile females (but not males) become progressively more likely to join the adult females in territorial defence with age, and their behaviour is affected by both the number of defending adults and the number of intruders. We interpret the ability of juveniles to assess relative numbers as an adaptation for assessing the risk of territorial conflict according to their own fighting ability, and the ability of their pride of successfully defend the territory. The difference between the sexes reflects the greater value of the natal territory to philopatric females. Adult females display a variety of strategies when defending the territory, including unconditional and conditional forms of cooperation. We show here that individuals display the rudiments of these strategies as juveniles.     

Sex and social play in juvenile rats (Rattus norvegicus).

Four experiments were conducted to examine the effects of pretest social isolation, sex of the social stimulus, and test cage familiarity on sex differences in play fighting in 156 juvenile Long-Evans rats. Reliable sex differences were found only when Ss were tested after 6 days of isolation in undisturbed cages (Exp III). In contrast to weak sex effects, pretest isolation and test cage familiarity were robust variables influencing levels of play fighting in juveniles of both sexes. Results are discussed in reference to procedural differences among experimental approaches that have examined sex differences in social play. It is suggested that social investigatory behavior and play behavior appear to be reciprocally related. Hence, the sex difference in social play is accompanied by an apparent reversal in the sex effect seen with social investigation. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of prior reinforcement on the interaction of observer pairs.

"The hypothesis that the interaction of observer pairs is a function of the degree of prior reinforcement of the judgment responses was tested on 38 Ss who first made judgments of lengths of lines when alone, and then in pairs. The pairs were so chosen that the alone judgments of the two Ss overlapped minimally… . On the basis of these findings it is concluded that Ss with a past history of positive reinforcement in a given type of judgment are less influenced by their partners in a group judgment situation than Ss with a history of negative reinforcement." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Playing with the face: Playful facial “chattering” and signal modulation in a monkey species (Theropithecus gelada).

Darwin (1872), in The expression of emotions in man and animals, underlined that human facial expressions represent a shared heritage of our species with nonhuman primates. Play is a fertile field to examine the role of facial expressions that we share with our common ancestors because the primate play face is homologous to human laughter. Here, we focus on the use of two playful expression variants (PF: play face, mouth opened with only the lower teeth exposed; FPF: full play face, lower/upper teeth and gums exposed via the actively retraction of the upper lip) in Theropithecus gelada. During ontogeny PF was replaced by FPF; in older subjects PF was virtually absent. The ontogenetic transition appears to reflect the phylogenetic sequence of the two playful displays with FPF considered a derived form of PF. This age-trend bias of facial displays is probably due to their different roles in communication. The correspondence between facial signals emitted and elicited is a valuable criterion to evaluate playmates' attentional state. Adults were more sensitive than immatures in responding to the play faces of others. Probably, previous playful experience, social competence, and neural circuit maturation are at the basis of adult sensitiveness. Similar to humans, where unconscious laughing is deserved for close friends and/or relatives, FPF was extremely frequent during gelada mother-offspring play. Probably, under some intimate circumstances, facial displays should be primarily linked to the spontaneous expression of emotional states of the sender more than to the strategic transfer of actual information to the receiver. (PsycINFO Database Record (c) 2011 APA, all rights reserved)