Multimicroelectrode stimulation within the cat L6 spinal cord: influences of electrode combinations and stimulus interleave time on knee joint extension torque.

During multimicroelectrode stimulation within the cat L6 spinal cord, the number of electrodes activated, their separation distance, and the stimulus interleave time all influenced isometric knee joint extension torque. The torque evoked by stimulation with a three electrode combination could be enhanced or suppressed when compared with that evoked by single or paired electrode stimulation. A similar difference was noted when comparing two electrode combination versus single electrode stimulation. Relative fatigue was not improved significantly by interleaving the stimuli from two or three microelectrodes. Compared with the extension torque response evoked by noninterleaved stimulation, torque evoked by interleaved stimulation with the two microelectrode combination was decreased when the electrode distance was 2.0 mm or less and increased when the electrode distance was 3.0 mm. Designing an optimal stimulation strategy for multimicroelectrode spinal cord stimulation will be challenging and complex if a suppression effect among these electrodes is to be avoided. To reduce muscle fatigue, an asynchronous, interleaved strategy of stimulation may be required.