Dorsolateral frontal lobe lesions and behavior in the macaque: Dissociation of threat and aggression

Abstract

Eight male juvenile rhesus monkeys (Macaca Mulatta) were housed in an enclosure and observed for a period of 13 months. During that time, each animal sustained dorsolateral frontal lobe resection. Two monkeys were removed from the group and one operated until four were lesioned; the remaining four animals were then lesioned en bloc. Observations on the group were analyzed at three points: one monkey lesioned, four lesioned, and all eight lesioned. Several social behaviors were recorded over the course of the experiment and both individual and group levels compared over observation periods. Although preopreative relationships, levels of affiliative interaction, and, for the most part, order of dominance remained stable after surgery, marked changes in aggression and threat behavior were seen. The diminution in occurrence of threats and concomitant increase in aggression are viewed as supportive of a model of frontal lobe function incorporating stimulus processing properties and lack of inhibition. This theoretical position is used to explain complementary results found in both the laboratory and field settings.