The reticulospinal tracts are a major descending system, but their role in motor control has received limited study. Understanding reticulospinal function is important because when brain injuries affect cortex, extrapyramidal systems like the reticulospinal system may be critical for functional recovery. The present investigations are designed to reveal the function of reticulospinal outputs originating in the pontomedullary reticular formation (PMRF), in nucleus reticularis gigantocellularis and nucleus reticularis pontis caudalis. Experiments for Aim 1 are designed to measure reticulospinal outputs to muscles of the arm and shoulder girdle bilaterally (24 muscles). Understanding how arm muscles are controlled bilaterally by the reticulospinal system will permit understanding of this systems capacity for contribution to functional recovery after stroke. Experiments for Aims 2-3 explore mechanisms for corticospinal and reticulospinal interaction in the control of movement.
Aim 2 uses physiological methods to study corticoreticular coordination through paired stimulus-triggered averaging studies in the cortical motor areas (Ml, SMA, and PMd) and the PMRF. Experiments for Aim 3 will use neuroanatomical methods to reveal the sources of corticospinal cells with collaterals to reticulospinal cells and to determine the strengths of projections from SMA, PM, and Ml to the reticulospinal system. Combined, Aims 2 and 3 examine substrates for coordination of corticospinal and reticulospinal control of movement. Experiments for Aim 4 will test for kinematic and kinetic coding in the activity of PMRF neurons, testing for directional tuning and coding of force. Together, these experiments will measure the outputs and functions of the reticulospinal system along with the relevant sources of input from cortical projections for the preparation and performance of reaching. Much of the focus will be on coordination of bilateral arm movements, which is proposed to be a key function of the reticulospinal system. Bilateral coordination of arm movements is important for functional activities, such as wheelchair mobility, walking with assistive devices, and bed mobility, which are central to neurological rehabilitation after stroke. Thus, the proposed studies will significantly extend our understanding of a critical but poorly understood part of the motor control system of the brain. ? ?
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