Mouse killing in rats: a comparison of spontaneous killers and rats with lesions of the medial hypothalamus or the medial accumbens nucleus.

Mouse killing was observed and videotaped at forty-eight hr following surgery in rats with lesions of the medial hypothalamus or the medial accumbens. The initial attacks and killing bites of the lesioned rats were directed at the anterior dorsal surface, predominantly to the regions of the neck, shoulders, and thorax and did not differ from those of spontaneous mouse killing rats. The latency to attack was significantly shorter for the lesioned animals but the time required to kill following the attack tended to be longer. Lesioned animals spent significantly more time biting the prey following the kill and left significantly more bite marks on the prey than did the spontaneous killers. When the dead prey was moved about the cage following the kill, the lesioned animals showed a significantly greater tendency to attack it than did the spontaneous killers. Following the test of mouse killing, each rat was successively exposed to a freshly killed mouse, a cotton wad, and a wood block. The lesioned animals attacked the dead mouse and the cotton wad as though they were live mice whereas the spontaneous killers did not. These results suggest that while the killing is similar for lesioned and spontaneous killers, the lesioned animals show a heightened response to the killing experience. This is manifested in an exaggeration of attack behaviors toward prey and prey-like stimulus objects following an initial killing experience.