Stimulus novelty as a factor in the intraspecific pain-associated aggression of domesticated rats

Familiar and unfamiliar pairs of male Sprague-Dawley rats were exposed to ascending and descending series of shocks of constant intensity and varying duration. It was found that, while unfamiliar pairs exhibited significantly more aggression than did familiar pairs when subjected to short-duration shocks (.05 and.1 sec), there was no difference between the groups at longer shock durations (.2,.3, and.5 sec).