1. Introduction

Neuromodulation or brain stimulation techniques that are now available in clinics[1– 3] include deep brain stimulation (DBS), [3, 4] epidural cortical stimulation (ECS), [5] vagus nerve stimulation (VNS), [6] cranial electrotherapy stimulation (CES), [7] trigeminal nerve stimulation (TNS), [8] transcranial direct current stimulation (tDCS), [9] and repetitive transcranial magnetic stimulation (rTMS).[10, 11] Although multiple brain stimulation techniques have been developed, they all face inherent limitations in their applications. For example, deep brain stimulation (DBS) requires complex neurosurgery and is invasive; epidural cortical stimulation (ECS), vagus nerve stimulation (VNS), and transcranial direct current stimulation (tDCS) all have poor spatial resolution; repetitive transcranial magnetic stimulation (rTMS), although noninvasive due to the inductive nature of magnetic stimulation, has a focal spot size of several centimeters and cannot be used for deeper brain stimulation. Therefore, novel brain stimulation methods that can overcome these limitations are under intensive investigation. Among these new methods, a low-intensity focused ultrasound stimulation (FUS) has been proven to have noninvasiveness, high spatial resolution, and deep penetration.[12– 14]

Previous studies using FUS in animal and human experiments have shown that low-intensity ultrasound has the ability to modify the excitability of neuronal tissue.[15– 17] This effect has been further investigated by using focused ultrasound to modulate the function of regional brain tissue in mice and rabbits, as well as monkeys’ visuomotor behavior, and the activity of the primary somatosensory cortex of humans.[18] However, the relationship between the local field potential (LFP) power spectrum and ultrasonic power during FUS is still not fully understood. An important key parameter in neuromodulation, the LFP power spectrum can provide the LFP energy intensity of brain rhythms at different frequency bands. Therefore, a better understanding of the relationship between the LFP power spectrum and ultrasonic power is important as a basis for studying the effects of FUS on neuromodulation and providing a reference for setting ultrasonic power during FUS.

In the present paper, the relationship between ultrasonic power and the LFP power spectrum at the delta, theta, alpha, beta, and gamma frequency bands were extensively studied. As a control (CTRL), the LFP signals of the rat hippocampus were first recorded without FUS. After the LFP signals were recorded without FUS, the signals at the same position were recorded under FUS at various ultrasonic powers. The LFP power spectrums at delta, theta, alpha, beta or gamma frequency bands were calculated by the Welch algorithm.