OtherOriginal ArticleFocused Ultrasound-mediated Non-invasive Brain Stimulation: Examination of Sonication Parameters

•The 'sweet-spot' in excitatory neuromodulation of pulsed FUS was identified.•1-5 ms TBD, 50% DC, 300 ms SD stimulates the somatomotor area at the lowest AIs.•The use of 350 kHz fundamental frequency outperforms 650 kHz.•The pulsed FUS outperforms the equivalent continuous sonication.

BackgroundTranscranial focused ultrasound (FUS) has emerged as a new brain stimulation modality. The range of sonication parameters for successful brain stimulation warrants further investigation.ObjectiveThe objective of this study was to examine the range of FUS sonication parameters that minimize the acoustic intensity/energy deposition while successfully stimulating the motor brain area in Sprague-Dawley rats.MethodsWe transcranially administered FUS to the somatomotor area of the rat brain and measured the acoustic intensity that caused excitatory effects with respect to different pulsing parameters (tone-burst duration, pulse-repetition frequency, duty cycle, and sonication duration) at 350 and 650 kHz of fundamental frequency.ResultsWe observed that motor responses were elicited at minimum threshold acoustic intensities (4.9-5.6 W/cm2 in spatial-peak pulse-average intensity; 2.5-2.8 W/cm2 in spatial-peak temporal-average intensity) in a limited range of sonication parameters, i.e. 1-5 ms of tone-burst duration, 50% of duty cycle, and 300 ms of sonication duration, at 350 kHz fundamental frequency. We also found that the pulsed sonication elicited motor responses at lower acoustic intensities than its equivalent continuous sonication.ConclusionOur results suggest that the pulsed application of FUS selectively stimulates specific brain areas-of-interest at an acoustic intensity that is compatible with regulatory safety limits on biological tissue, thus allowing for potential applications in neurotherapeutics.