Invertebrate learning and memory: from behavior to molecules.

Classical ethologists have provided a long and rich tradition of stud ying the learning and memory capabilities of a variety of invertebrate animals (Schneirla 1929, von Frisch 1950, Lindauer 1960). In recent years, however, interest in this field has been renewed because it has become clear that many invertebrate animals can provide powerful model systems in which to explore the cellular and molecular mechanisms of learning and memory. Thus, a variety of disciplines such as neuroethology, psychology, and modern neurobiology have merged in a concerted effort to develop invertebrate preparations in which these combined approaches can be focused on the general theme of the cellular basis of behavioral plasticity. This overall strategy has come to be known as a "simple-systems" approach to the study of learning and memory. A "simple-systems" approach is not the exclusive domain of invertebrate research. The general strategy of such an approach is to try to identify neural circuits involved in a particular form oflearning and then attempt to specify the precise locus and nature of the cellular changes that are involved. This approach has been successfully applied in a number of vertebrate systems. These include eyeblink conditioning in the cat (Kim et al 1983, Woody et a1 1983, Woody 1984), cardiac conditioning in the pigeon (Cohen 1980, 1984), and conditioning of the nictitating membrane response in rabbit (Thompson et a1 1983, 1984, Moore et a1 1982, Harvey et aI 1985), as well as cellular analog systems in cerebellum (Ito 1982), the red nucleus (Tskahara, 1984), and hippocampus (McNaughton et al 1 978, Levy &