Control of Reafference in Posture and Locomotion

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Resistance reflexes help an animal to counter external forces that would move its limbs, thus they help maintain a stable posture. During voluntary movement, those same resistance reflexes must be disabled or reversed to allow the movement to occur. This study asks how the resistance reflexes are organized to allow an animal to maintain a static posture, and how they are disabled and transformed into assistance reflexes at the onset of voluntary movements. While these questions have been approached in vertebrates, insects and crustaceans, answers are far from complete. The questions in the current study will be addressed in the crayfish because relevant circuitry for leg movements has been described in terms of a set of identified sensory neurons, interneurons and motor neurons, and their synaptic interactions. The investigators will use three approaches: (i) in vivo motion analysis and nerve recordings; (ii) a hybrid in vitro preparation/neuromechanical model; and (iii) a neuromechanical simulation of the crayfish body and nervous system. This approach will reveal how the animal controls its reflexes to help stabilize posture and assist voluntary movements underwater and on land, where the set of external forces are very different. The mechanisms discovered here are likely to be used by other legged animals. The approach employs two new tools developed by the principal investigator's laboratory, the AnimatLab neuromechanical simulation software and the hybrid neuromechanical interface that links a model to the nervous system of the experimental preparation. AnimatLab is freely available at www.animatlab.com, and the hybrid interface will be made into a commercial-grade electronic instrument. The research will provide training in neurophysiology, behavioral analysis and computational neuroscience to undergraduate and graduate students who include members of underrepresented populations. Those students will participate in helping to teach relevant portions of the summer B.R.A.I.N. course at Georgia State University for outstanding undergraduates from around the country.