Pathways of the past: the imprint of memory

Memory is central to many aspects of behaviour, but in spite of a long interest in its neural basis, empirical evidence of the nature of the hypothetical pathway that is left in the vertebrate central nervous system by learning has been elusive. An important impediment has been the difficulty of localizing a brain region in which information is stored, but this difficulty has largely been overcome in the case of the learning process of visual imprinting. Most theories of memory suppose that an experience or event leads to the formation or strengthening of particular pathways in the brain. The evidence that is derived from imprinting partly supports this view, but the processes involved are more complex and more interesting than has been supposed.