Effects of hippocampal lesions on competitive behavior in rats

In Experiment 1, groups containing three rats each competed against each other in paired competition until a hierarchial pattern stabilized. The competition involved one rat pushing another out of a tube to reach the reinforcement. In each triad, the middle-ranked rat was given a bilateral hippocampectomy or cortical control lesion. When tested postoperatively in paired competition, the rats with hippocampal lesions won and lost in the same pattern as cortical controls whether tested with previous partners or with winners and losers they had not previously encountered. These hippocampal rats, compared with cortical controls, were significantly impaired on a passive avoidance test. In Experiment 2, rats were lesioned prior to testing in paired competition. Without prior competitive experience, rats with hippocampal lesions lost significantly more of their bouts than the cortical control pairs. Thus, when animals had not been given prior competitive experience, hippocampal lesions resulted in their losing consistently.