Ultrasound Stimulations Induce Prolonged Depolarization and Fast Action Potentials in Leech Neurons

Ultrasound stimulation (US) carries the promise of a selective, reversible, and non-invasive modulation of neural activity without the need for genetic manipulation of neural structures. However, the mechanisms of US-induced generation of action potentials (APs) are still unclear. Here we address this issue by analyzing intracellularly recorded responses to controlled delivery of US of leech nociceptive neurons. US induced a depolarization linearly accumulating in time and outlasting the duration of the stimulation. Spiking activity was reliably induced for an optimal US intensity range. Moreover, we found that APs induced by US differ in smaller amplitude and faster repolarization from those induced by electrical (EL) stimulation in the same cell, but keep the same repolarization rate. These results shed light on the mechanism by which spikes are induced by US and pave the way for designing more efficient US patterns.