Fear response and aggressive behavior of hippocampectomized house rats

Abstract

Hippocampectomized house rats (hippocampal group) were prepared, and their fear response to a live cat and aggressive behavior toward fellow animals were compared with those of normal control animals and control with localized cortical damage (cortical control group). Fear response was assessed by comparing the number of interruptions of the beam farthest from the cat with that of the nearest beam, and also by comparing the amount of food and water consumed in the presence of the cat with the amount consumed during the cat's absence. Aggressive behavior was assessed by the number of spontaneous and shock-provoked reciprocal attacks, initiated attack, defense and facing that occurred between animals belonging to the same group as well as to other groups. In the presence of a cat, the ratio of the farthest beam interruptions to the nearest beam interruptions was significantly lower, and the amount of food consumption was reliably larger in the hippocampal group than in the 2 control groups. Therefore, hippocampectomy was thought to reduce fear significantly. Spontaneously as well as provoked by electric shock, the hippocampectomized animal tended to reciprocate or initiate attack less frequently than did the 2 control groups. Although less impressive, hippocampectomy was thought to reduce aggressive behavior. From the above results, the hippocampus was inferred to facilitate fear response as well as aggressive behavior, the former significantly and the latter less conspicuously.