As animals and humans grow and develop, the organization of neural networks that control behavior must adapt to changes in the morphology and biomechanics of their peripheral targets in order that the organism may continue to function properly over the course of its life. Learning plays a critical role both in the establishment of initial performance early in development, and in the maintenance of performance during growth. In addition, recovery from pathological states depends critically upon the ability of motor networks to adapt their activity to the altered morphology and biomechanical properties of their peripheral targets. This proposal will use toads as a model system for studies of motor learning. The toad feeding model will be used because it involves a simple, easily observable and quantifiable behavior that generates clear predications for theories of motor learning at the levels of performance, motor output and neural networks. The model system involves recovery of feeding behavior that generates clear predictions for theories of motor learning at the levels of performance, motor output and neural networks. The model system involves recovery of feeding behavior following bilateral transection of the hypoglossal nerves. Hypoglossal transection has two effects on feeding behavior. It alters the sensory input normally associated with feeding behavior, and it inactivates the tongue protractor muscles. Preliminary results show that toads learn to compensate for both of these changes and regain the ability to feed successfully during repeated trials following hypoglossal nerve transection. The proposed experiments will: (1) describe changes in the kinematics of head, jaw and tongue movements during repeated feeding trials after bypoglossal transection; (2) describe learned changes in the activity of jaw and forelimb muscles; (3) examine how practice regimes affect rates of motor learning; (4) explore pathways in the central nervous system for sensory feedback correction of feeding motor output during motor learning; and (5) investigate the role of sensory feedback in maintaining the correspondence between motor output and performance in normal subjects. The proposed studies will contribute significantly to an understanding of motor learning in vertebrates, and will help to bridge the gap between studies of human performance on the one hand and neural networks on the other.
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