Our research focuses on the production and control of locomotor behavior in the lamprey, with the goal of understanding behavior at the systems level. We propose three areas of investigation, two are continuations of previously begun projects, and one is new: I. Investigation of the structure and function of the spinal central pattern generator (CPG for locomotion, especially the intersegmental coordinating system. We will estimate functional coupling strengths in the CPG by fitting stochastic models to experimental data. Inhibitory baths of varying lengths will be used to study the relative strength of long versus short connections. Perturbations produced by bending the spinal cord with be used to help distinguish between ascending and descending coupling. Besides entraining the CPG, bending (forcing) elicts a slowly-decaying decrease in cycle period; we will search for a similar slow process in unforced data. We will extend the theoretical framework for entrainment by including long distance and non- relative-phase coupling; experimentally, we will determine how entrainment ranges vary with the number of active segments. Connectionist models of the CPG will be used to explore the dependence of intersegmental phase lags on the lengths and strengths of connections as well as the spatial variation in oscillator frequencies. We will analyze models of coupled heterogeneous populations of bursting neurons and explore the relevance of heterogeneity to intersegmental coordination. On a new experimental front, we will explore the use of optical dyes to record from groups of neurons in the CPG circuit, as well as to identify new classes of coordinating neurons. II. Normal locomotor behavior: integration of the components of the body to produce whole animal swimming. This is largely a continuation of work begun the last grant cycle. We will explore the role of the water in producing the traveling wave, the role of sensory inputs on the pattern, and the interaction between the brainstem and spinal cord. By combining all of these aspects of locomotor control, we are working toward a complete understanding of the production of an entire behavior in a vertebrate, and how all the parts of the organism and its environment combine and interact to produce that behavior. III. Longitudinal studies of the development and adaptability of the lamprey locomotor CPG. This is a new direction for the lab. The fictive swimming all sized of larval lampreys obtainable will be recorded, and the coupling strength among the segments estimated. If the motor pattern of the spinal cords of any size behaves very differently from the adults, new stochastic models will be used for the estimations. Also, we will raise animals under a variety of test to test the plasticity and adaptability of the CPG.
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