A cellular analysis of the fundamental neurobehavioral questions of central programs, sensory feedback to these programs, and higher-order control of such processes can be employed to demonstrate how individual neurons interact in the production of a set of behavioral acts. This investigation will provide a quantitative description of neuronal circuitry underlying discrete behavioral processes. This will be accomplished by employing the pulmonate mollusc, Hiliosoma which performs complex behaviors under conditions that allow direct analyses of neural activity. With the CNS completely exposed for intracellular microelectrode recordings from its readily identifiable neurons, this animal displays the majority of acts in its behavioral repertoire in an unaltered fashion. The specific aims of this proposal are: 1) to continue elucidation of the neural interactions which constitute a central program, 2) to demonstrate how sensory information can modulate the output of such programs, and 3) to define higher-order mechanisms for initiating and controlling such motor outputs. We will construct testable models of neuronal circuitry for several interacting behaviors by employing a variety of technical approaches which provide both physiological and morphological data on each neuron participating in the generation of these motor outputs. This description will include not only an 'averaged' picture of neuronal interactions, but will also stress the limits of variability inherent in the circuitry of individual animals and the effect of such variability on the generation of, and control of motor output. Such variability can be reproducibly obtained through genetic and developmental manipulations of laboratory populations. This investigation will result in a detailed description of neural control of discrete behaviors and the interaction of neural elements controlling different behaviors. It will further provide a basis for understanding the effects of genetically and developmentally derived variability at the cellular level.