Oppositions, joints, and targets: the attractors that are the glue of social interactions.

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.

Play fighting and the development of the social brain: The rat's tale.

The benefits gained by young animals engaging in play fighting have been a subject of conjecture for over a hundred years. Progress in understanding the behavioral development of play fighting and the underlying neurobiology of laboratory rats has produced a coherent model that sheds light on this matter. Depriving rats of typical peer-peer play experience during the juvenile period leads to adults with socio-cognitive deficiencies and these are correlated with physiological and anatomical changes to the neurons of the prefrontal cortex, especially the medial prefrontal cortex.

Is play a behavior system, and, if so, what kind?

Given that many behavior patterns cluster together in sequences that are organized to solve specific problems (e.g., foraging), a fruitful perspective within which to study behaviors is as distinct 'behavior systems'.

"I am going to groom you": Multiple forms of play fighting in gray mouse lemurs (Microcebus murinus).

Play fighting is a commonly reported form of play that involves competitive interactions that generally do not escalate to serious fighting. Although in many species what are competed over are the body targets that are bitten or struck in serious fighting, for many others, the competition can be over other forms of contact, such as sex, social grooming, and predation. In primates, the most detailed studies have been of species such as Old World monkeys, that engage in play fighting that simulates serious fighting, but reports of a number of others, especially among nocturnal prosimians, have noted that play fighting can also involve simulation of sex and grooming.

What is play fighting and what is it good for?

Play fighting is a common form of play reported among species of mammals, birds, and some other taxa. The competition present in play fighting revolves around gaining some advantage, such as biting a partner without being bitten. The behavior simulated during play fighting need not be restricted to that present in adult serious fighting, but can involve competitive interactions derived from amicable behavior, such as sex and social grooming, or from nonsocial competition, such as predation.

From Play to Aggression: High-Frequency 50-kHz Ultrasonic Vocalizations as Play and Appeasement Signals in Rats.

When rats engage in playful interactions, they emit appetitive 50-kHz ultrasonic vocalizations (USVs). We investigated the role of 50-kHz USVs in the playful behavior of both juvenile and adult rats. A cohort of juvenile rats was surgically devocalized and allowed to interact with either devocalized or intact partners as juveniles and again as adults.

Peering into the dynamics of social interactions: measuring play fighting in rats.

Play fighting in the rat involves attack and defense of the nape of the neck, which if contacted, is gently nuzzled with the snout. Because the movements of one animal are countered by the actions of its partner, play fighting is a complex, dynamic interaction. This dynamic complexity raises methodological problems about what to score for experimental studies.

Anatomy is important, but need not be destiny: novel uses of the thumb in aye-ayes compared to other lemurs.

Aye-ayes (Daubentonia madagascerensis) have highly specialized hands with long digits, especially the thin middle one (D3), which is used for extracting food, such as beetle larvae, under bark. Due to the elongation of their fingers, including the thumb, it is presumed that aye-ayes have a rather limited capacity for delicate manipulation of objects. However, studies have reported independent movement of digits D3 and D4, and one report noted a seemingly independent thumb (D1) movement in holding food.

The use of the bared-teeth display during play fighting in Tonkean macaques (Macaca tonkeana): sometimes it is all about oneself.

Play signals are viewed as important means by which animals inform each other that bites, strikes, and throws that occur during play fighting are indeed playful rather than serious. One such signal is the open mouth play face that is common in primates and many other mammals. Unfortunately, as most play fighting involves biting, it can be ambiguous as to whether any instance of opening the mouth is performed to communicate playful intent or is simply a preparation for biting.

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.