No change in intermale aggression after amygdala lesions which reduce freezing

Long-Evans rats with bilateral lesions in the area of the amygdala, or operated controls, were tested with strange male intruders into the subjects' home cages. Various measures of attack toward the intruder, including piloerection, lateral attack, on-top-of and biting showed no difference between the experimental and control animals. However, subjects with amygdaloid damage showed a substantial and significant reduction in freezing in the presence of a cat. This finding of reduced defensiveness to a predator is consistent with previous findings for amygdala lesions, while the failure to find decrements in conspecific offensive attack agrees with some, but not all, previous work in this area. The finding that a clear decrement in defense occurs in the same amygdala-lesioned subjects showing no suggestion of a reduction in offense adds to a body of data which indicates that offense and defense respond differentially to manipulation of a number of important neural and neurochemical systems.