Neural bases of recognition memory investigated through an analysis of imprinting

Abstract

Through a learning process known as imprinting, the young of some animals, including the domestic chick, come to recognize an object by being exposed to it. Visually naive chicks vigorously approach a wide range of objects. After an adequate period of exposure to one object chicks selectively approach it in a recognition test. The nervous system of dark-reared chicks is not a tabula rasa , as chicks have predispositions to approach some stimuli rather than others. Nevertheless, visual imprinting leads to changes in a nervous system that may not have been ‘marked’ by previous visual experience, and so encourages the hope of discovering the neural bases of the learning process. The intermediate and medial part of the hyperstriatum ventrale, a sheet of cells within the cerebral hemispheres, plays a crucial role in visual imprinting, particularly in the memory process of recognition. The cellular and sub-cellular changes that take place in this part of the hyperstriatum ventrale after imprinting are described. The right and left hyperstriatum ventrale regions play different roles in the imprinting process, and evidence is given for the existence of multiple memory systems in the chick brain.