Abstract
The dynamic aspect of behavior is exaggerated during social interactions such as sex, combat and rough-and-tumble play where the movements of the two animals involved continually influence one another. The behavioral 'markers' abstracted from this stream can greatly influence the conclusions drawn about the effects of experimental procedures and how changes during development are interpreted. By using methods of analysis that treat behaving systems as being dynamic and governed by negative feedback processes, the behavioral markers that are abstracted can more accurately reflect the underlying mechanisms. Using examples from rats engaged in play fighting, serious fighting and food defense, it is shown that motivational from non-motivational contributions to behavioral output and changes in that output with age can be discerned. For example, while sex differences in the frequency of initiating play by juvenile rats are shown to reflect differences in the motivation to engage in this behavior, sex differences in preferred motor patterns used during play do not. Rather, they reflect differences in perceptual and motor systems. Although an issue that is often neglected, we show that behavioral description, and the theoretical underpinnings of that description, is critical for the study of the mechanisms that produce and regulate behavior.