Focused Ultrasound Neuromodulation (FUS) for Prolonged Suppression of Pain Related Potentials

Abstract

Chronic pain has a major impact on quality of life. Treatment options for chronic pain include device-based electrical stimulation or pharmaceutical solutions. The challenges of these treatment options include safety of long-term application or patient addiction (to opioids-based drug therapies). Focused ultrasound (FUS) waves have emerged as a promising therapeutic tool for non-invasive neuromodulation of the central and peripheral nervous system. In this work, we investigated, through high-resolution acoustic imaging and custom designed phantoms, the attenuation effect of various skin layers on acoustic intensity and spatial resolution for noninvasive modulation of peripheral nerves. We also investigated, for the first time, the prolonged effect of noninvasive low-frequency low-intensity ultrasound in suppression of pain-evoked potentials in the reflex arc neural pathway in anesthetized animal. The experiments included applying US to electrically stimulated rat sciatic nerve (simulating pain potentials) at increasing sonication time (30, 60, 90 secs) and at varying duty cycle (31.25, 50, and 80 percent) and measuring resulting pain potentials through Electromyography (EMG) recordings. We found that increasing sonication time and duty cycle enhanced the prolonged suppression of pain related potentials. The US treatment also caused a shift in the median of the frequency components in the power spectrum of the EMG measurements. This indicates activation of new muscle fibers, possibly to compensate for activity suppression brought on by the US. This is interesting given we still observed a drop in both area under the curve (AUC) and amplitude of EMG. Overall, the study shows the potential to tune the prolonged suppressive effect of US on pain potentials, sheds light on potential changes in muscle fiber activation due to US, and paves the way for potential applications of US in device-based treatment of chronic pain.