Effects of Varying Pulse Width and Frequency of Wireless Stimulation in Rat Sciatic Nerve

Abstract

Peripheral nerve stimulation is a commonly used method for assisting movements after spinal cord injury, stroke, traumatic brain injury, and other types of neurological damage or dysfunction. There are many different patterns of electrical stimulation used to accomplish movement. And so, our study investigated stimulation with a wireless floating microelectrode array (WFMA) in comparison to previously reported data on functional electrical stimulation. To determine the effect on hindlimb movement, we tested a range of frequencies and pulse widths using WFMAs that were implanted in the rat sciatic nerve for 38 weeks. Frequencies between 1 and 50 Hz did not change the minimum current amplitude required to elicit movement in the hindlimb. Increasing pulse width from 57.2 to 400.4 µs decreased the minimum current required but had an associated increase in total charge applied per pulse. Overall, the WFMA provides a stable wireless peripheral nerve interface suitable for functional electrical stimulation.Clinical Relevance- This work establishes the efficacy of various stimulation parameters for controlling movement with a wireless peripheral nerve stimulator.

Figure 1.

Wireless floating microelectrode array (WFMA) after implantation in the rat sciatic nerve. Device is secured with a silicone epoxy (green).

Figure 2.

Baseline current thresholds for motor recruitment (I_th) for each animal in the study. Stimulation frequency was at 1 Hz and pulse width was set to 200.2 μs. All data were recorded during the final stimulation testing session on post-implantation week 38. For each animal, the mean value of all electrodes evoking movement is indicated by a “+” symbol.

Figure 3.

Current thresholds for motor recruitment (I_th) as a function of frequency (pulse width set to 200.2 μs). Error bars represent standard deviation across six animal subjects implanted with a WFMA.

Figure 4.

Current thresholds for motor recruitment (I_th) as a function of pulse width (frequency set to 1 Hz) plotted on left y-axis. Charge per pulse required for motor recruitment (Q_th), calculated from I_th values, plotted on right y-axis. Error bars represent standard deviation across six animal subjects implanted with a WFMA.

Figure 5.

Current thresholds for motor recruitment (I_th) as a function of pulse width (frequency set to 1 Hz) for each animal (ID listed at top of each graph). Charge values (Q_th) were calculated from I_th values and are plotted in blue with values corresponding to the right y-axis. Data shows average and standard deviation for all electrodes generating movement in the hindlimb on week 38 post-implantation (n listed in top right corner of each plot).