TH-202. Investigating the effects of cerebellar transcranial ultrasound stimulation on motor cortex excitability

Abstract Transcranial focused ultrasound stimulation (TUS) is a novel non-invasive brain stimulation technique that uses acoustic waves to alter neuronal excitability. We investigated the effects of cerebellar TUS (cbTUS) on motor cortex (M1) excitability. We hypothesized that 1) longer cbTUS duration will induce greater inhibition of M1 excitability; 2) TUS will lower M1 excitability post-sonication; 3) cbTUS of lobule VIII will have greater inhibition compared to Crus I/II. Real cbTUS consisted of sonication at 20 W whereas sham consisted of 0 W. A 12 kHz tone mask was used. In Experiment 1, cbTUS was applied to Crus I/II and motor evoked potentials (MEPs) from transcranial magnetic stimulation of contralateral M1 were measured at pre-TUS, after 150 ms, 300 ms, and 450 ms of TUS, and 150 ms following 500 ms of TUS. We observed that longer sonication duration induced greater inhibition. In Experiment 2 we assessed longer latencies post-sonication and compared Crus I/II stimulation to lobule VIII. We found inhibition following 450 ms of cbTUS and at 150 ms post 500 ms sonication. However, MEPs 150 ms post-real TUS did not differ from sham. No effect of stimulation location was found. In Experiment 3, we tested primarily 0 W sham and included two active sham conditions: 450ms of 20 W TUS targeting V1, and 450 ms of 20 W stimulation with the transducer facing away from the scalp. A real stimulation condition of 450 ms cbTUS was included. Results show that inhibition occurred post-sonication and following 450 ms of sham stimulation, due to an inhibitory effect of the sound mask. MEPs following 450 ms of real cbTUS was lower than 450 ms of sham stimulations. This shows that cbTUS can inhibit M1 excitability and is the first demonstration of an effect of cerebellar TUS in humans. Research Category and Technology and Methods Basic Research: 6. Pulsed Ultrasound (pUS) Keywords: MEP, Brain stimulation, Cerebellum, Neuromodulation