LESIONS OF THE LD1BIC SYSTEM: THEIR EFFECT ON THE AGONISTIC BEHAVIOUR OF THE PIGEOn

Lesions in the archistriatum, the avian homologue of the amygdala, and the nucleus striae terminalis suppress the aggressive behaviour and enhance the avoidance behaviour of selected aggressive pigeons. Similar limbic circuits thus seem to control aggression in birds and mammals. It is well documented in mammals that the limbic system plays an important role in the control of aggression. For birds, the evidence on this is still fragmentary but they may grossly conform. We have examined the effect of coagulating lesions in the archistriatum, the avian homologue of the amygdala, and in the nucleus striae terminalis, the septal termination of the main archistriatal efferent pathway, the tractus occipito-mesencephalicus. Before we could proceed with the lesion study it was necessary to develop a test that would allow an assessment of agonistic behaviour. Eventually we settled on a simple test consisting of introducing in a standardized manner a stick and a human hand into the home cage of each pigeon. For routine scoring, the response of a pigeon to a stick or hand test was classed either attack, threat, retreat or fleeing, depending on the reactions predominantly shown by the bird. The distinct behaviour patterns that were shown during each test were also noted. The hand test released relatively more attack, retreat and fleeing scores than the stick test which yielded predominantly threat behaviour. Since we were mainly interested in aggressive behaviour we selected 30 pigeons that consistently responded to the test stimuli with aggressive responses, namely wing slapping and pecking. These were randomly assigned to three groups: in 12 animals we attempted placing