Periodic and Aperiodic Neural Responses to Transcranial Focused Ultrasound Stimulation: An EEG Investigation

Transcranial ultrasound stimulation (TUS) is an emerging neuromodulation technique with promising therapeutic potential, while our understanding about its fundamental neurophysiological effects is still rudimentary. This study investigated the complex dynamics of both periodic oscillations and aperiodic neural activity induced by TUS in 22 healthy participants using electroencephalography (EEG). We stimulated the left primary motor cortex (M1) by TUS and recorded 64-channel EEG across the periods of pre-TUS, during TUS, and post-TUS. We observed distinct temporal patterns across different frequency bands: enhanced alpha power during TUS (p = 0.013), suppressed delta activity during TUS (p = 0.010), and pronounced low gamma band suppression during TUS (p < 0.001), all showing significant post-stimulation recovery. Analysis of the aperiodic component revealed significantly elevated spectral exponent during active TUS compared to sham (1.34 vs 1.14, p < 0.001), followed by a significant post-stimulation reversal that persisted in specific regions (left M1: d = -0.573; right PMC: d = -0.706). The neuromodulation effects showed clear spatial specificity, with robust effects not only at the stimulation site (left M1, Cohen's d = 1.028 but also in connected motor regions (left PMC: d = 0.961; right M1: d = 0.893). These findings provide novel insights into the neurophysiological effects of ultrasonic neuromodulation.