Playing with play : movement and experience in the development of play fighting in rats

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Foroud, Afra
University of Lethbridge. Faculty of Arts and Science
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Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2002
Playing with Play: Movement and experience in the development of play fighting in rats. Juvenile rats are more gentle in the way they play fight than are adult rats. I used Laban Movement Analysis (LMA), a form of movement notation used in the theatre arts, to identify and characterize the movements that underlie this age-related difference in 'roughness'. To standardize the behavioural context for comparison, the rats were compared when in the 'pinning' configuration. During a 'pin', the attacker stands over the supine defender. In the first experiment, male and female rats, from the juvenile phase to early adulthood were videotaped and analyzed using LMA. The results show that with age, rats become more 'forceful' in the way they move. In part, this change in 'forcefulness' seems to be related to the degree of control an individual exercises, over its own body, and that of its partner. I have identified a reliable and objective behavioural makre for such 'control'. This marker, which I call anchoring, can be scored without prior knowledge of LMA. When anchored, the attacker stand with its hind feet on the ground and its fore feet on the supine defender, whereas when unanchored, the attacker stands on the defender with all four feet. With increasing age, the proportion of occasions with the attacker being anchored increases. One possibility is that younger rats are motorically less competent to gain and maintain an anchored posture. Therefore, in a second experiment, playful pins were anlayzed from around the time of weaning, when play fighting first begins, and onwards. The infant rats were just as able to anchor during pins as were postpubertal rats, and so motoric immaturity cannot account for the reduced levels of anchoring in juveniles. Additional experiments were conducted in an attempt understand what modulates this development modulation in anchoring. Thus, in the third main experiment of this study, rats were reared in isoloation from weaning and tested socially once at 30, 60 and 90 days. The results show that the age-related changes in anchoring is not dependent on social experience. Finally, in the fourth experiment, the cortex was removed in neonatal rats, and their play was examined from the juvenile period onwards. Anchoring in decorticates does not show the developmental modulation present in intact rats, rather, anchoring remains at the juvenile typical level at all ages. These data include that the developmental changes in anchoring are regulated by cortical mechanisms. The findings from this thesis suggest that juveniles have an age-modulated change in how strongly the rats control their own movements and those of their partners during play fighting. That is, juveniles exhibit reduced control just when they are the most playful. This reduced control may increase the range and variability of experiences gained during play fighting, and so may have evolved to maximize the benefits to be gained by engaging in play at the juvenile phase of the life cycle.
xiii, 130 leaves ; 28 cm.
Rats -- Behavior , Animal fighting , Dissertations, Academic