This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Spinal neurons play a crucial role in generating voluntary limb movements. We are continuing to investigate the way that spinal interneurons are engaged in controlling muscle synergies by documenting their responses in monkeys performing a repertoire of movements about the wrist (flexion-extension, radial-ulnar deviation, pronation-supination and grip). Most interneurons in cervical segments were modulated during one or more of these hand movements, showing preferential relationships to particular muscle patterns. We have also been documenting the response patterns of motor cortical cells during the same response repertoire to compare the tuning properties of cortical and spinal neurons. We also documented the output effects on muscles evoked by intraspinal stimulation at different cervical sites. In behaving monkeys the excitatory and inhibitory post-stimulus effects evoked by single intraspinal stimuli in upper and lower cervical segments were investigated by stimulus-triggered averages of muscle EMG. At most spinal sites the stimuli evoked responses in multiple muscles indicating that intraspinal sites could be useful for evoking synergistic muscle responses. Recent experiments showed that a monkey could control intraspinal stimulation by modulating the high-frequency power in the cortical field potential. The intraspinal stimulation evoked EMG activity that was converted to movement of a cursor into a target, demonstrating for the first time that volitional control of cortical potentials can be used to generate goal-directed output from spinal stimulation.
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