The generation of task-dependent and goal-directed walking behaviour requires feedback from leg sense organs for regulating and adapting the ongoing motor activity. Sensory feedback from movement and force sensors influences the magnitude and the timing of neural activity generated in the neural networks driving individual joints of a leg. In many animals, the effects of sensory feedback on the generated motor output change between posture maintenance and locomotion. These changes can occur as reflex reversals in which sensory information, that usually counteract perturbations in posture control, instead reinforce movements in walking. In stick insects, for example, flexion of the femur-tibia joint is measured by the femoral chordotonal organ, which mediates reinforcement of the stance phase motor output of the femur-tibia joint when the locomotor system is active. Flexion signals promote flexor and inhibit extensor motoneuron activity. However, the mechanisms underlying these changes are only partially understood. Therefore, the purpose of the present thesis was to investigate whether the processing of movement and position signals of the FTi joint is task-specifically modified in the generation of adaptive leg movements, which is required when locomotion is adapted to changes in walking direction or in turning movements. To study the role of these task-dependent changes in walking behaviour on the processing of local sensory signals, the generation of reflex reversals mediated by the femoral chordotonal organ in the femur-tibia joint of the stick insect Carausius morosus was measured in a semi-intact walking preparation. In several experimental conditions either in front, in one or both middle or in hind legs, the femoral chordotonal organ was mechanically displaced and the motoneuronal responses in the flexor and extensor tibia were monitored, while the remaining legs performed either forward, backward or curve walking on a slippery surface. I demonstrated that the occurrence of reflex reversals depends on the specific motor behaviour executed. While in forward walking flexion signals from the front leg fCO regularly elicit reflex reversal in the tibial motoneurons, this cannot be observed in backward walking. Similarly, during optomotor-induced curve walking, reflex reversal occurred reliably in the middle leg on the inside of the turn, however not in the contralateral leg on the outside of the turn. Thus, the experiments revealed that the nervous system modulates proprioceptive reflexes in individual legs during task-specific walking adaptation. Furthermore, I showed that nonspiking interneurons, known to be involved in the premotor network of the FTi joint, participate in reflex responses in both the inner and outer middle leg during curve walking. First results show that the reflex response in some interneuron types is altered between the inner and outer leg, while no differences were found in others.
Task-specific modulation of a proprioceptive reflex in a walking insect
2012-05-07
Hellekes, Katja (2012). Task-specific modulation of a proprioceptive reflex in a walking insect. PhD thesis, Universität zu Köln.
Theses
Electronic Resource
German , English
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