Imprinting, learning, and memory.

If a visually naive chick is exposed to one of a wide range of conspicuous objects, the chick may learn its characteristics. A series of biochemical studies has implicated a restricted part of the forebrain in this process of imprinting; a specific region (IMHV) has been identified which may be a site of information storage. Changes in the morphology of synapses occur in this region as a consequence of training. The left and right IMHV regions play different roles in the imprinting process. Exposure to a simple artificial object, a rotating red box, has different neural consequences from those associated with exposure to a complex object, a rotating stuffed jungle fowl, which resembles a conspecific. These differences may be related to the differences in complexity of the two training objects. Another possibility is that two neural systems are implicated in imprinting: a system that underlies a predisposition to approach objects resembling conspecifics and a learning system, of which IMHV is a crucial component, that is engaged by particular objects and that in "natural" circumstances also allows the chick to learn the characteristics of its mother.