We thank the Harry Frank Guggenheim Foundation and the Natural Science and Engineering Research Council of Canada for grants to SMP that supported the research leading to the development of these methods.

1. Equipment and Room Set Up
<ol>
	<li>The play box apparatus is a clear, Plexiglas box measuring 50 cm X 50 cm X 50 cm with 1-2 cm of standard corncob bedding.</li>
	<li>All filming is conducted in the dark via a handheld camcorder under the night-shot option.</li>
	<li>The camcorder is placed at a 45&deg; angle facing downwards towards the play box on a tripod. All four corners must be visible in the shot to obtain a full view of the apparatus.</li>
</ol>
2. Methodology
<ol>
	<li>Animals are...

<ol>
	<li>Aldis, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Play Fighting. , (1975).</li><li>Blanchard, R. J., Blanchard, D. C., Takahashi, T., Kelley, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Attack+and+defensive+behaviour+in+the+albino+rat.">Attack and defensive behaviour in the albino rat.</a> Anim. Behav. 25, 622-634 (1977).</li><li>Fagen, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Animal Play Behavior. , (1981).</li><li>Field, E. F., Watson, N. V., Whishaw, I. Q., Pellis, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Play-fighting+in+androgen-insensitive+tfm+rats:+Evidence+that+androgen+receptors+are+critical+for+the+development+of+adult+playful+defense+but+not+playful+attack.">Play-fighting in androgen-insensitive tfm rats: Evidence that androgen receptors are critical for the development of adult playful defense but not playful attack.</a> Dev. Psychobiol. 48, 111-120 (2006).</li><li>Geist, V., Krames, L., Pliner, P., Alloway, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+weapons,+combat+and+ecology.">On weapons, combat and ecology.</a> Advances in the Study of Communication and Affect. 4, 1-30 (1978).</li><li>Kamitakahara, H., Monfils, M. -. H., Forgie, M. L., Kolb, B., Pellis, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+modulation+of+play+fighting+in+rats:+Role+of+the+motor+cortex.">The modulation of play fighting in rats: Role of the motor cortex.</a> Behav. Neurosci. 121, 164-176 (2007).</li><li>Kolb, B., Kolb, B., Tees, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prefrontal+cortex.">Prefrontal cortex.</a> The Cerebral Cortex of the Rat. , 437-458 (1990).</li><li>Meaney, M. J., Stewart, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+descriptive+study+of+social+development+in+the+rat+(Rattus+norvegicus.">A descriptive study of social development in the rat (Rattus norvegicus.</a> Anim. Behav. 29, 34-45 (1981).</li><li>Panksepp, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+ontogeny+of+play+in+rats.">The ontogeny of play in rats.</a> Dev. Psychobiol. 14, 327-332 (1981).</li><li>Panksepp, J., Normansell, L., Cox, J. F., Siviy, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+neonatal+decortication+on+the+social+play+of+juvenile+rats.">Effects of neonatal decortication on the social play of juvenile rats.</a> Physiology and Behavior. 56, 429-443 (1994).</li><li>Pellis, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Agonistic+versus+amicable+targets+of+attack+and+defense:+Consequences+for+the+origin,+function+and+descriptive+classification+of+play-fighting.">Agonistic versus amicable targets of attack and defense: Consequences for the origin, function and descriptive classification of play-fighting.</a> Aggress. Behav. 14, 85-104 (1988).</li><li>Pellis, S. M., Bekoff, M., Allen, C., Burghardt, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keeping+in+touch:+Play+fighting+and+social+knowledge.">Keeping in touch: Play fighting and social knowledge.</a> The Cognitive Animal: Empirical and Theoretical Perspectives on Animal Cognition. , 421-427 (2002).</li><li>Pellis, S. M., Bell, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Closing+the+circle+between+perceptions+and+behavior:+A+cybernetic+view+of+behavior+and+its+consequences+for+studying+motivation+and+development.">Closing the circle between perceptions and behavior: A cybernetic view of behavior and its consequences for studying motivation and development.</a> Dev. Cog. Neurosci. 1, 404-413 (2011).</li><li>Pellis, S. M., McKenna, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intrinsic+and+extrinsic+influences+on+play+fighting+in+rats:+Effects+of+dominance,+partner's+playfulness,+temperament+and+neonatal+exposure+to+testosterone+propionate.">Intrinsic and extrinsic influences on play fighting in rats: Effects of dominance, partner's playfulness, temperament and neonatal exposure to testosterone propionate.</a> Behav. Brain Res. 50, 135-145 (1992).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Play-fighting+differs+from+serious+fighting+in+both+target+of+attack+and+tactics+of+fighting+in+the+laboratory+rat+Rattus+norvegicus.">Play-fighting differs from serious fighting in both target of attack and tactics of fighting in the laboratory rat Rattus norvegicus.</a> Aggress. Behav. 13, 227-242 (1987).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+rates+of+attack,+defense+and+counterattack+during+the+developmental+decrease+in+play+fighting+by+male+and+female+rats.">Differential rates of attack, defense and counterattack during the developmental decrease in play fighting by male and female rats.</a> Dev. Psychobiol. 23, 215-231 (1990).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Attack+and+defense+during+play+fighting+appear+to+be+motivationally+independent+behaviors+in+muroid+rodents.">Attack and defense during play fighting appear to be motivationally independent behaviors in muroid rodents.</a> Psych. Rec. 41, 175-184 (1991).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+reversal+changes+during+the+ontogeny+of+play+fighting+in+male+rats:+Attack+versus+defense.">Role reversal changes during the ontogeny of play fighting in male rats: Attack versus defense.</a> Aggress. Behav. 17, 179-189 (1991).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Juvenilized+play+fighting+in+subordinate+male+rats.">Juvenilized play fighting in subordinate male rats.</a> Aggress. Behav. 18, 449-457 (1992).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+pre-juvenile+onset+of+play+fighting+in+rats+(Rattus+norvegicus.">The pre-juvenile onset of play fighting in rats (Rattus norvegicus.</a> Dev. Psychobiol. 31, 193-205 (1997).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+play+fighting+of+rats+in+comparative+perspective:+A+schema+for+neurobehavioral+analyses.">The play fighting of rats in comparative perspective: A schema for neurobehavioral analyses.</a> Neurosci. Biobehav. Rev. 23, 87-101 (1998).</li><li>Pellis, S. M., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Playful+Brain.">The Playful Brain.</a> Venturing to the Limits of Neuroscience. , (2009).</li><li>Pellis, S. M., Pellis, V. C., Dewsbury, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Different+levels+of+complexity+in+the+playfighting+by+muroid+rodents+appear+to+result+from+different+levels+of+intensity+of+attack+and+defense.">Different levels of complexity in the playfighting by muroid rodents appear to result from different levels of intensity of attack and defense.</a> Aggress. Behav. 15, 297-310 (1989).</li><li>Pellis, S. M., Pellis, V. C., McKenna, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Some+subordinates+are+more+equal+than+others:+Play+fighting+amongst+adult+subordinate+male+rats.">Some subordinates are more equal than others: Play fighting amongst adult subordinate male rats.</a> Aggress. Behav. 19, 385-393 (1993).</li><li>Pellis, S. M., Pellis, V. C., McKenna, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+feminine+dimension+in+the+play+fighting+of+rats+(Rattus+norvegicus)+and+its+defeminization+neonatally+by+androgens.">A feminine dimension in the play fighting of rats (Rattus norvegicus) and its defeminization neonatally by androgens.</a> J. Comp. Psych. 108, 68-73 (1994).</li><li>Pellis, S. M., Pellis, V. C., Whishaw, I. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+the+cortex+in+play+fighting+by+rats:+Developmental+and+evolutionary+implications.">The role of the cortex in play fighting by rats: Developmental and evolutionary implications.</a> Brain Behav. Evol. 39, 270-284 (1992).</li><li>Pellis, S. M., Field, E. F., Smith, L. K., Pellis, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+differences+in+the+play+fighting+of+male+and+female+rats.+Implications+for+the+causes+and+functions+of+play.">Multiple differences in the play fighting of male and female rats. Implications for the causes and functions of play.</a> Neurosci. Biobehav. Rev. 21, 105-120 (1997).</li><li>Pellis, S. M., Pellis, V. C., Pierce, J. D., Dewsbury, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disentangling+the+contribution+of+the+attacker+from+that+of+the+defender+in+the+differences+in+the+intraspecific+fighting+of+two+species+of+voles.">Disentangling the contribution of the attacker from that of the defender in the differences in the intraspecific fighting of two species of voles.</a> Aggress. Behav. 18, 425-435 (1992).</li><li>Pellis, S. M., Hastings, E., Shimizu, T., Kamitakahara, H., Komorowska, J., Forgie, M. L., Kolb, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+orbital+frontal+cortex+damage+on+the+modulation+of+defensive+responses+by+rats+in+playful+and+non-playful+social+contexts.">The effects of orbital frontal cortex damage on the modulation of defensive responses by rats in playful and non-playful social contexts.</a> Behav. Neurosci. 120, 72-84 (2006).</li><li>Reinhart, C. J., Pellis, S. M., McIntyre, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+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.">The 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.</a> Dev. Psychobiol. 45, 83-92 (2004).</li><li>Reinhart, C. J., Metz, G., Pellis, S. M., McIntyre, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Play+fighting+between+kindling-prone+(FAST)+and+kindling-resistant+(SLOW)+rats.">Play fighting between kindling-prone (FAST) and kindling-resistant (SLOW) rats.</a> J. Comp. Psych. 120, 19-30 (2006).</li><li>Siviy, S. M., Panksepp, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sensory+modulation+of+juvenile+play+in+rats.">Sensory modulation of juvenile play in rats.</a> Dev. Psychobiol. 20, 39-55 (1987).</li><li>Siviy, S. M., Baliko, C. N., Bowers, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rough-and-tumble+play+behavior+in+Fischer-344+and+buffalo+rats:+Effects+of+social+isolation.">Rough-and-tumble play behavior in Fischer-344 and buffalo rats: Effects of social isolation.</a> Physiol. Behav. 61, 597-602 (1997).</li><li>Siviy, S. M., Love, N. J., DeCicco, B. M., Giordano, S. B., Seifert, T. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+relative+playfulness+of+juvenile+Lewis+and+Fischer-344+rats.">The relative playfulness of juvenile Lewis and Fischer-344 rats.</a> Physiol. Behav. 80, 385-394 (2003).</li><li>Smith, L. K., Fantella, S. -. L., Pellis, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Playful+defensive+responses+in+adult+male+rats+depend+upon+the+status+of+the+unfamiliar+opponent.">Playful defensive responses in adult male rats depend upon the status of the unfamiliar opponent.</a> Aggress. Behav. 25, 141-152 (1999).</li><li>Smith, L. K., Forgie, M. L., Pellis, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+underlying+the+absence+of+the+pubertal+shift+in+the+playful+defense+of+female+rats.">Mechanisms underlying the absence of the pubertal shift in the playful defense of female rats.</a> Dev. Psychobiol. 33, 147-156 (1998).</li><li>Takahashi, L. K., Lore, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Play+fighting+and+the+development+of+agonistic+behavior+in+male+and+female+rats.">Play fighting and the development of agonistic behavior in male and female rats.</a> Aggress. Behav. 9, 217-227 (1983).</li><li>Taylor, G. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fighting+in+juvenile+rats+and+the+ontogeny+of+agonistic+behavior.">Fighting in juvenile rats and the ontogeny of agonistic behavior.</a> J. Comp. Physiol. Psych. 94, 953-961 (1980).</li><li>Thor, D. H., Holloway, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Play+solicitation+behavior+in+juvenile+male+and+female+rats.">Play solicitation behavior in juvenile male and female rats.</a> Anim. Learn. Behav. 11, 173-178 (1983).</li><li>Thor, D. H., Holloway, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developmental+analysis+of+social+play+behavior+in+juvenile+rats.">Developmental analysis of social play behavior in juvenile rats.</a> Bull. Psychon. Soc. 22, 587-590 (1984).</li><li>Vanderschuren, L. J. M. J., Niesink, R. J. M., van Ree, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+neurobiology+of+play+behavior+in+rats.">The neurobiology of play behavior in rats.</a> Neurosci. Biobehav. Rev. 21, 309-326 (1997).</li><li>Whishaw, I. Q., Kolb, B., Tees, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+decorticate+rat.">The decorticate rat.</a> Cerebral cortex of the rat. , 239-268 (1990).</li></ol>

No conflicts of interest declared.

Play fighting is a complex, dynamic interaction in which the participants continually influence each other's behavior. As a consequence, a scoring scheme that is sensitive to those dynamics and the contingent nature of the actions performed is needed. The scheme outlined in this paper has proven successful in comparing across sexes, individual differences, through development, strain differences and for experimental treatments4, 14, 16, 20, 24, 29, 30, 31, 32, 32, 36. Moreover, the scheme presented can...

Rats have been the most intensively used animals in the laboratory with which to study play10, 21, 41, and several attempts have been made to develop scoring schemes to measure the effects of experimental treatments on play fighting8, 9, 37, 38, 39. However, while these schemes have had some success in monitoring the frequency of play, they are less suitable as ways to monitor changes in the content of play due to their lack of sensitivity to the dynamics of the interaction13. The main problem is that, during fighting, the use of tactics by one partner is often contingent on the performance of particular tactics by the other2, 15. We have developed a scoring scheme that takes the dynamics of the interaction into account and so is better suited to detect and characterize the subtle changes that occur during play with experimental manipulation16, 20, 26. In this paper, we focus on the measurement of the defensive tactics performed by the recipient of a playful attack.
During serious fighting, animals attack and defend particular body targets, using species-typical weapon systems5. In rats, the primary weapons are the teeth, which are used to bite the flanks and lower dorsum2. Such serious fighting is readily exhibited in a resident-intruder context, in which an unfamiliar adult male is introduced into the cage of a resident adult male2, 15. As in serious fighting, in play fighting, animals also compete to gain some advantage over one another1. Rats, for example, attack and defend the nape of the neck15, which if contacted is gently nuzzled with the snout11, 32. Therefore, it is possible to discern playful attacks from aggressive attacks based not only on the manner of physical interactions (nuzzle vs. bite), but also on the body targets attacked (nape vs. flanks and lower dorsum). In addition, such playful nuzzling should not be confused with social investigation or allogrooming. Social investigation involves sniffing the partner, most frequently on the face and anogenital area. Because these behaviors appear to coincide with playful behaviors, and therefore may be considered aspects of playful interactions, it has been shown that these social interactions precede play behavior. Furthermore, changes in the motivation to engage in social investigation are independent of comparable changes in play9. There are several features that distinguish allogrooming from play20. First, allogrooming usually occurs when the rats huddle together following a protracted period of playing. Second, while playful attack is centered on the nape, allogrooming can involve contact with many parts of the partner's body, although it sometimes is focused on the nape. Third, this grooming involves gentle nibbling and pulling of the partner's fur with the teeth. Fourth, unlike allogrooming, most playful attacks to the nape are defended by the recipient, which leads to complex sequences of wrestling.
The main focus of this paper is to show what may be fruitfully measured during those complex sequences of play that can include wrestling. As shown below, the various tactics used by the defender to protect its nape lead to different possible outcomes. These outcomes, such as wrestling on the ground, boxing or chasing, have in some studies been measured as independent behavior patterns, but we have found that, in the majority of cases, these outcomes depend on the defensive tactic adopted by the recipient of a nape attack15. For example, evasive tactics often lead to chases and rolling over onto the back leads to wrestling. Thus, outcome based measurements, such as boxing and wrestling, are actually composites arising from the actions of both participants. Using a dynamic approach, our framework provides a means of scoring moments in the interaction when the actions measured are attributable to only one of the participants28, an approach that will be more evident to the reader once the examples of how the measuring framework is used are presented.
As shown in Figure 1, the rat on the left is seen approaching another from the rear (a) and then pouncing toward the nape of its neck (b). However, before contact is made, the defender rotates around the longitudinal axis of its body (c) to face its attacker (d). As the attacker moves forward, the defender is pushed onto its side (e), but then rolls over onto its back as the attacker continues to reach for its nape (f-h). From the supine position, the defender launches an attack toward its partner's nape (i), but is blocked by its partner's hind foot (j, k). Following another attempt to gain access to its partner's nape, the rat on top is pushed off (l) by the supine animal's hind feet (m), which thus enables the original defender to regain its footing (n) and lunge to attack its partner's nape (o).
<img src="/files/ftp_upload/4288/4288fig1.jpg" alt="Figure 1"/> 
Figure 1. A pair of juvenile male rats is shown attacking and defending the nape during a play fight. From Pellis &amp; Pellis15; reprinted with permission of John Wiley &amp; Sons.

<table border="1">
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 <td>Equipment</td>
 <td>Comments (optional)</td>
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 <td>Sony DCR-DVD103 Camcorder</td>
 <td>Optical Zoom- 20x, Night shot 
 *See Below</td>
 </tr>
 <tr>
 <td>Play Apparatus</td>
 <td>50 X 50 X 50 cm Plexiglas</td>
 </tr>
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 	<td></td>
 <td>* Any camcorder will work for recording, although an optical zoom of 20x or above is desired for optimal zoom.</td>
 </tr>
 </tbody>
</table>

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. We present a scoring schema that is sensitive to the correlated nature of the actions performed. The frequency of play fighting can be measured by counting the number of playful nape attacks occurring per unit time. However, playful defense, as it can only occur in response to attack, is necessarily a contingent measure that is best measured as a percentage (#attacks defended/total # attacks X 100%). How a particular attack is defended against can involve one of several tactics, and these are contingent on defense having taken place; consequently, the type of defense is also best expressed contingently as a percentage. Two experiments illustrate how these measurements can be used to detect the effect of brain damage on play fighting even when there is no effect on overall playfulness. That is, the schema presented here is designed to detect and evaluate changes in the content of play following an experimental treatment.

Two studies illustrate how the multi-faceted scoring scheme that we have developed can be used to diagnose the effects of experimental manipulations on the play fighting of rats. The first shows that the method can be used to pinpoint the specific component of play changed by an experimental manipulation and the second shows how the method can be used to measure changes in the relationships following an experimental manipulation.
(1) The effects of neonatal decortication
<p class="jove_...

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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. We present a scoring schema that is sensitive to the correlated nature of the actions performed. Two experiments illustrate how these measurements can be used to detect the effect of brain damage on play fighting even when there is no effect on overall playfulness. That is, the schema presented here is designed to detect and evaluate changes in the content of play following an experimental treatment.

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 ...

peering-into-dynamics-social-interactions-measuring-play-fighting

Research

JoVE Journal

Neuroscience

15.1K Views.  University of Lethbridge. 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. We present a scoring schema that is sensitive to the correlated nature of the actions performed. Two experiments ...