Lay Abstract for NSF Proposal # 0544639, "Comparative aspects of goal-oriented locomotion in decapod crustaceans"
Early in the twentieth century, the Russian physiologist Nikolai Bernstein posed what has come to be known as "the degrees of freedom problem": most movements can, in principle, be produced by an infinite number of different combinations of muscle activity. For example, a human reaching in space can attain a target through various combinations of motion at the shoulder, elbow, and wrist. How does the nervous system choose among all of the possible ways of producing a desired motion? Is the same motion always produced by the same combination of muscle activations? Is this combination constant across motions, individuals, or even species? Despite several decades of research, we still do not have clear answers to these questions. Certainly part of the difficulty, at least in mammalian systems, is the number of elements involved: even motion involving just a single joint typically requires several muscles and the activity of hundreds, if not thousands, of motor units. This project will approach the degrees of freedom problem using legged locomotion in crabs (Carcinus, primarily a sideways-walking crab, and Libinia, primarily a forwards-walking crab) as a model system. Movements of each leg in these animals are controlled by only a few dozen motor units. Dr Belanger will take advantage of the fact that crabs will orient to and track plumes of attractive odorant (typically indicating a food source). This is a natural behavior, and one that allows him to predict an area through which the animal will locomote at a relatively constant speed. Animals will be placed in a small recirculating flume, with an odor source at the upstream end. The source will be placed so that the resulting plume of odorant passes through a "target area" in the center of the flume. As the animal follows the odor plume and passes through this area, multiple video cameras will monitor the movements of each of the limb segments. A 3 D motion analysis system will be used to derive the corresponding changes in joint angles. Simultaneously, the electrical activity of leg muscles will be recorded to determine the patterns of muscle activation underlying these movements. With these data Dr Belanger can begin to ask how (or if) muscle activation differs for particular movements across individuals and species, and how similar sets of muscles are used to produce both forwards and sideways locomotion. In addition to answering a fundamental question in motor control, these data will be extremely useful to engineers designing biomimetic robots and smart prostheses. This project will provide multidisciplinary training for both graduate and undergraduate students, in a region designated as an EPSCoR state. In particular, undergraduate participants in the project will be recruited, via Louisiana State University's summer research programs, from historically black colleges in Louisiana and Mississippi, and from primarily Hispanic schools in Texas.
