Neural Mechanisms of Task Specific Changes in Sensorimotor Processing

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When animals move through their environment, they need to generate a motor output suitable for both propulsion as well as directing the animal towards goals that have been identified by means of visual, chemosensory, auditory or tactile cues. In the course of this task locomotor activity is modified to allow for the generation of curvatures in the locomotor path or to surpass or climb over obstacles. The neural networks generating the motor output for locomotion are localized in the segmented central nervous systems at the level of the locomotor organs: in insects, for example, these networks reside in the thoracic nerve cord. To generate locomotor behavior, these networks are under continuous descending control from higher brain regions. The descending signals not only maintain motor activity, but also allow for continuous modification and adjustment of the actual locomotor output to serve the behavioral needs described above. A change in walking direction is a simple and often necessary maneuver for approaching a goal. Asymmetric kinematics of leg movements on either side allow for such maneuver. At present it is not clear, how signals from higher order centers in the brain influence the segmental networks and which component neurons of the locomotor networks are affected in the course of generating goal directed locomotor behavior. This project aims to close this gap in knowledge working on the stick insect, an animal for which considerable detailed information on the role of segmental sensory feedback in the generation of single leg stepping is available. Previous studies in this animal gave rise to the hypothesis that modifications in the processing of sensory feedback within the segmental networks might in general contribute to such modifications. The project shall answer the following questions: 1. What modifications occur in the influence and processing of sensory feedback from ground contact, movement and load sensors in dependence of the behavioral task a single leg has to serve, i.e. as an outside or an inside leg in curve walking? 2. How is processing of movement signals underlying reinforcement of movement modified in order to serve the control of motor activity on either side of a curve walking animal? 3. Which component neurons in the segmental premotor network are influenced in order to allow for the above described modifications in the generation of a motor output for curve walking?