Abstracts

Rationale: Pharmaceutical intervention to treat epilepsy can be quite successful, but in the case of refractory epilepsy, these pharmaceutical interventions are not effective. Many refractory epilepsy patients turn to implantable neurostimulator devices such as vagus nerve stimulation (VNS) or responsive neurostimulation (RNS;) however, these devices have their own limitations including finite battery life, large size, and the negative side effects caused by the tethered cuff electrode. To potentially solve these issues, a miniature wirelessly powered and controlled implantable device consisting only of the required circuitry to perform stimulation was designed. The capability of the stimulator was also improved by utilizing interferential current stimulation (ICS) also known as temporal interference stimulation, a technique where two independent stimulation signals interfere to create a more-localized stimulation signal. Since the stimulation only occurs at a localized region, a looser-fitting cuff electrode can be utilized.

Methods: A wireless, miniature electronic stimulator was acutely implanted in the hindlimb of a female, urethane-anesthetized Long-Evans rat with a cuff electrode around the sciatic nerve. The sciatic nerve was chosen for its ease of access and easily identifiable response to stimulation. The device was driven using two amplitude modulated radio frequency (RF) signals which the device demodulated into the two stimulation signals, sine waves at 2kHz and 2.01kHz which interfered to produce a 10Hz beat frequency stimulation signal. An electromyogram (EMG) was recorded by suturing stainless steel electrodes to the biceps femoris muscle which were connected to a custom recording device.

Results: EMG data shows muscle contractions occurring at a 10Hz frequency during the period when both RF power sources are enabled, but no contractions were observed when only one or no RF signal was present. When the RF amplitude was increased with only a single channel enabled, tetanic conduction block was observed. No response was seen after the nerve was transected.

Conclusions: Since the muscular contraction was only present during RF powering when the cuff electrode was placed around a healthy nerve, it can be concluded that the demodulated RF signal was stimulating the nerve rather than electromagnetic radiation stimulating the muscle or nerve directly. The fact that the muscle was contracting at the beat frequency of 10Hz, demonstrates that effective ICS was utilized. The combination of two minimally sized, wirelessly driven stimulators allows for multiple stimulation techniques to be utilized with the same implantation setup, from conduction block to bipolar stimulation at a desired frequency, to ICS while eliminating the need for a battery-change surgery. Peripheral nerves can effectively be stimulated using this technique which could potentially improve neuromodulation techniques for the treatment of refractory epilepsy by providing additional treatment options for patients while reducing the severity of potential side effects.

Funding: Please list any funding that was received in support of this abstract.: NIH OD023847.