The role of a restricted region of the chick forebrain in the recognition of individual conspecifics.

It has been proposed that there are two neural systems underlying filial preference behaviour in the domestic chick. Firstly, a predisposition which serves to orient the chick towards objects resembling adult fowl, and secondly a learning system which is engaged by particular objects, including the bird's own mother. Lesions to a particular region of the chick forebrain, the intermediate and medial part of the hyperstriatum ventrale (IMHV), impairs the learning system but not the predisposition. The present experiment was designed to test the hypothesis that the IMHV is involved in learning to recognise individual members of a species. Between 6 and 10 h after chicks had hatched, bilateral lesions were placed in the IMHV (n = 16), and the Wulst (n = 16). There were 52 sham-operated controls. Following recovery from surgery (20-28 h later), all chicks were exposed to one of two stuffed jungle fowl for 4 X 50 min. Two hours after the final training session all birds were given a preference test. This test involved the simultaneous presentation of the fowl to which the chicks had previously been exposed and the fowl which they had not previously seen. While both the sham-operated and the Wulst-lesioned groups had a significant mean preference for the fowl to which they had been exposed during training, the IMHV-lesioned birds had no preference. This result is consistent with the hypothesis that IMHV is involved in learning to recognise individual birds, as well as other conspicuous objects.