Thirty years of collaboration with Gabriel Horn.

All the collaborative work described in this review was on the process of behavioural imprinting occurring early in the life of domestic chicks. Finding a link between learning and a change in the brain was only a first step in establishing a representation of the imprinting object. A series of overlapping experiments were necessary to eliminate alternative explanations. Once completed, a structure, the intermediate and medial mesopallium (IMM), was found to be strongly linked to the formation of a neural representation of the object used for imprinting the birds. With the site identified, lesion experiments showed that it was necessary for imprinting but not associative learning. Also the two sides of the brain responded differently with the left IMM acting as a permanent store and the right side acting as a way station to other parts of the brain. The collaborative work led to many studies by Gabriel Horn with others on the molecular and cellular bases of imprinting, and also to neural net modelling and behavioural studies with me on the nature of category formation in intact animals.