CONTROL OF VOLUNTARY LIMB MOVEMENTS BY SPINAL CORD

University Of Washington, Seattle WA

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Abstract

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. Intraspinal stimulation is a promising method for evoking limb movements for prosthetic purposes since it recruits motor units in a more natural order than intramuscular stimulation, and can activate synergistic muscles in a coordinated manner. Toward this application we have been developing long-term indwelling stimulating electrodes and documenting the output effects on muscles evoked by intraspinal stimulation at different cervical sites. The best intraspinal electrodes so far consist of fine floating wires or sharpened microelectrodes. At most cervical spinal sites brief trains of stimuli evoked responses in multiple hand and forearm muscles, indicating that such sites could be useful for evoking synergistic muscle responses. However, there is no reliable somatotopic map for these effects because they are evoked via variable mixtures of passing fibers. Recent experiments tested whether a monkey could generate goal-directed cursor movements by intraspinal stimulation triggered from cortical electrical activity. The intraspinal stimuli were gated by increases in high-frequency power in motor cortical field potentials and evoked EMG activity that was converted to movements of a cursor into a target. This demonstrated for the first time that volitional control of cortical potentials can be used to generate goal-directed output from spinal stimulation.