Closed-Loop Plantar Cutaneous Augmentation by Electrical Nerve Stimulation Increases Ankle Plantarflexion During Treadmill Walking

Ankle plantarflexion plays an important role in forward propulsion and anterior-posterior balance during locomotion. This component of gait is often critically impacted by neurotraumas and neurological diseases. We hypothesized that augmenting plantar cutaneous feedback, via closed-loop distal-tibial nerve stimulation, could increase ankle plantarflexion during walking. To test the hypothesis, one intact rat walked on a motorized treadmill with implanted electronic device and electrodes for closed-loop neural recording and stimulation. Constant-current biphasic electrical pulse train was applied to distal-tibial nerve, based on electromyogram recorded from the medial gastrocnemius muscle, to be timed with the stance phase. The stimulation current threshold to evoke plantar cutaneous feedback was set at 30 mu A (1 center dot T), based on compound action potential evoked by stimulation. The maximum ankle joint angle at plantarflexion, during the application of stimulation currents of 3.3 center dot T and 6.6 center dot T, respectively, was increased from 149.4 degrees (baseline) to 165.4 degrees and 161.6 degrees. The minimum ankle joint angle at dorsiflexion was decreased from 59.4 degrees (baseline) to 53.1 degrees, during the application of stimulation currents of 3.3 center dot T, but not changed by 6.6 center dot T. Plantar cutaneous augmentation also changed other gait kinematic parameters. Stance duty factor was increased from 51.9% (baseline) to 65.7% and 64.0%, respectively, by 3.3 center dot T and 6.6 center dot T, primarily due to a decrease in swing duration. Cycle duration was consistently decreased by the stimulation. In the control trial after two stimulation trials, a strong after-effect was detected in overall gait kinematics as well as ankle plantarflexion, suggesting that this stimulation has the potential for producing long-term changes in gait kinematics.

Automated summary

Close-loop distal-tibial nerve stimulation to augment plantar cutaneous feedback increased ankle plantarflexion during walking and changed other gait kinematic parameters. A strong after-effect was detected in overall gait kinematics and ankle plantarflexion after stimulation trials, suggesting potential for producing long-term changes in gait kinematics.