This project will provide an analysis of higher-order neuronal control mechanisms. Specific attention will be directed to those cellular mechanisms that select which discrete motor outputs are coactivated to generate complex behavior patterns. This will be accomplished by employing the pulmonate mollusc, Helisoma, which continues to perform complex behaviors under conditions that allow direct analysis on identified neurons with the use of intracellular microelectrodes for recording, stimulating, and intracellular staining. We will examine, both physiologically and morphologically, the various higher-order interneurons that impinge upon the buccal ganglia and regulate both qualitative short-term neuronal mechanisms responsible for the orchestration of this complex behavior, this project will include studies of neuronal plasticity. These will utilize an in vivo culture method that allows assessment of long-term processes in this system. Questions about neuron-target interactions will be emphasized. A primary goal of these studies will be to determine what types of variability, in both neuronal form and function, indicate meaningful flexibility of neuronal capabilities as opposed to simply noise in an imperfect system. The mechanism of such flexibility will be explored.