Imprinting and the Neural Basis of Memory

Abstract

The way in which information acquired through learning processes is stored in the brain has long been a matter for speculation. During the 1960’s, however, some progress was made in the experimental analysis of the memory associated with habituation. This is a behavioural change, one component of which is that an animal gradually ceases to respond to a stimulus which is presented repeatedly; the absence of a response to the stimulus is an indication of a ‘memory’ not to respond. The scene was set for a cellular analysis of this memory when evidence appeared of changes in neuronal activity which resembled those of behavioural habituation (see for example Horn and Hill, 1964; Bruner and Tauc, 1966; Spencer et al., 1966a,b,c). On the basis of experimental evidence it was proposed (Bruner and Tauc, 1966) that the progressive reduction of a neuronal response in Aplysia is an expression of synaptic depression, and (Horn and Wright, 1970) that calcium ions are implicated in this process. Further support for both proposals came from subsequent studies of habituation in Aplysia (Kandel, 1979; Klein et al., 1980). Synaptic depression occurring in specific neural pathways can account for many aspects of behavioural habituation (Thompson and Spencer, 1966; Horn, 1967).