Our experiments are conducted in a preparation that has a relatively simple nervous system – the marine mollusc Aplysia californica. The central nervous system of this animal is distributed into several ganglia that contain a limited number of neurons, many of which are large and easily identifiable as unique individuals. Our experiments are multidisciplinary and utilize behavioral, morphological, electrophysiological, cell biological and molecular-biological approaches. In general, we study the neural basis of forms of behavioral plasticity that are due to changes in the internal state of an organism. Our primary interest is in mechanisms that establish internal states and in memory mechanisms that allow states to persist.