The proposed studies are designed to enhance our understanding of the functional role of the primate magnocellular red nucleus (RNm) in sensorimotor integration. Using several experimental conditions chosen to bring out important features of sensorimotor integration, the spatial and temporal properties of the relationship between RNm discharge and forelimb electromyographic (EMG) activity will be measured using time series analysis methods. This information is likely to aid our understanding of motor control in general and our understanding of disorders of movement control in patients suffering from brain trauma, amyolateral sclerosis, Huntington's disease and Parkinson's disease. RNm/EMG relations will be studied first during unloaded tracking movements. Single cell activity in RNm and EMG activity in 16 forelimb muscles will be recorded while the animal operates different tracking devices that elicit movement about finger, wrist, elbow and shoulder joints. Cross-correlation functions for each RNm/EMG pair will be used to identify the spatial patterns of muscle activation that occur in relation to RNm discharge and to quantify the timing relations between the RNm and limb muscles. The neuroanatomical of direct WGA-HRP will be injected into the RNm to demonstrate, via anterograde transport, the locations of direct projections to the ventral horn of the spinal cord. In the same animals, unconjugated HRP will be injected into muscles to demonstrated, via retrograde transport, the locations of specific motor neuron pools. Comparison of terminal and pool locations should reveal the muscles that receive direct input. A functional confirmation will provided by spike triggered averaging. Patterns of direct innervation will be compared with patterns revealed for the same cells by our cross-correlation analysis, which emphasizes the more powerful polysynaptic linkages. Next we will study the dynamical properties of RNm/EMG relations, and their dependence on mechanical load. Unexpected changes in elastic, inertial and torque loads will be applied during tracking movements. Coherence functions and impulse responses will be used to measure the dynamical properties of RN/EMG relations. These studies will test the hypothesis that the RNm codes movement velocity and will reveal the extent to which RNm neurons participate in adaptation to altered loading conditions. We will then determine whether RNm/EMG relations depend on the type of behavioral task. The sensory cue for a give movement will be varied by training the monkey to make tracking movements in tasks will be used to elicit different combinations of limb and digit use. In each case we will use time series analysis to measure the spatial and dynamical properties of RNm/EMG relations. These results will tell us whether RNm neurons are specialized to respond selectively when specific sensory cues, specific muscle activity patterns or other specific situations are encountered.
