Meeting Abstract
Multi-jointed limbs allow an animal to tune its motor output finely, but controlling the many degrees of freedom resulting from multi-jointed limbs is a well-recognized challenge. A central question in motor control is how the nervous system transforms larger behavioral goals into the complex computations necessary for the moment-by-moment control of multi-jointed limbs. Here we employ genetics, in-vivo electrophysiology, and quantitative analysis of leg kinematics and biomechanics to determine the respective contribution of circuits in the brain, the thoracic ganglia, sensory feedback and biomechanical properties of the limb to the generation of limb movements. By manipulating central control and sensory feedback under diverse preparations, we come to four conclusions regarding the control of leg movements in Drosophila. First, without sensory feedback from the environment, inter-leg coordination is disrupted. Second, in contrast to inter-leg coordination, many aspects of intra-leg coordination remain intact. In particular, retraction-protraction (RP) and extension-flexion (EF) are flexibly coordinated by central circuits such that a vast majority of movement epochs can be classified into a small number of discrete movement-types. Third, maintaining this structured movement requires descending inputs from the brain. Fourth, feedback from the environment seems critical for eliciting levation-depression movements which in turn structure movement into alternating stance and swing phases. We use this framework to underpin the role of descending neurons (DNs) from two different parts of the brain in shaping motor output by recording from them while measuring leg kinematics. In sum, there is a division of labor between feedforward and feedback which represents an elegant solution to the “degrees of freedom” problem.
