Play‐fighting is often difficult to differentiate from inhibited or immature serious fighting because both may utilize many of the same behavior patterns. In the rat the two behaviors involve different targets of attack. During play‐fighting, snout or oral contact is directed at the opponent's nape of the neck, whereas during serious fighting, male residents mostly direct their bites at the intruder's rump. Although similar to those used in serious fighting, the behavior patterns used during play‐fighting are modified to achieve the different targets of attack. Even though the tactics of attack and defense appear more adult‐like with increasing age, the playful targets persist well into adulthood.

During postweaning development, rats exhibit several well documented trends in their play fighting: (1) It peaks between 30-40 days and then declines with the approach of sexual maturity; (2) males initiate more play fights than females; and (3) the overall complexity of play fights, as expressed by such measures as duration of bouts, also decreases with increasing age. Such trends could arise from changes in attack or defense, or some combination of both. In this article it is shown that (a) the decline in play fighting with the onset of sexual maturity in rats results from a decline in attack, not in defense; (b) the differences in play fighting by male and female rats are due to sex-specific rates of both attack and defense; and (c) the developmental decrease in the complexity of play fighting arises from a decrease in the frequency of counterattacks (i.e., after an animal defends itself, it is less likely to launch an attack). In this way, age and sex differences in play fighting can be traced to differences in its subcomponents.

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Social play—that is, play directed toward others—is a readily recognizable feature of childhood. In nonhuman animals, social play, especially seemingly competitive rough-and-tumble play or play fighting, has been the most studied of all forms of play. After several decades of study, researchers of play fighting in laboratory rats have pieced together the rudiments of the neural mechanisms that regulate the expression of this behavior in the mammalian brain. Furthermore, the understanding of the organization, development, and neural control of play in rats has provided a model with which to examine how the experiences accrued during play fighting can lead to organizational changes in the brain, especially those areas involved in social behavior.

No abstract