In this vignette I want to show you an example of anodic field steering. Let me restate an important experimental condition, when the self-sizing-spiral cuff electrode is installed on the sciatic nerve there is no attempt to align a specific contact with a specific fascicle in the nerve. Stimuli applied to the individual branches of the sciatic nerve produced these torque profiles. Stimuli applied to the individual contacts produced these torque profiles. By chance, the 0˚, 90˚, and 180˚ contacts aligned closely enough with the tibial, medial gastrocnemius and lateral gastrocnemius branches that these fascicles could be fully activated before spillover of the stimulus current to other fascicles occurred. However, stimuli applied to the 270˚ contact appeared to initially recruit fibers in the common peroneal fascicle but then spread to the tibial fascicle and as the stimulus intensity increased, recruiting motor fibers in both fascicles. The application of an anodic stimulus to the 0˚ would be expected to suppress activation of the tibial fascicle when stimuli were applied to the 270˚. As the anodic steering current increased activation of the motor fibers in the tibial fascicle was suppressed. Let’s take another look at the effect of the anodic steering current.
Tarler, M.D. and J.T. Mortimer, “Selective and Independent Activation of Four Motor Fascicles Using a Four Contact Nerve Cuff Electrode”, IEEE Trans. on Rehabilitation Engineering, Vol 12, pp251-257. 2004.