Unilateral online ultrasound stimulation of early visual cortex suppresses responses to contralateral visual stimuli

Transcranial ultrasound stimulation (TUS) shows great promise for inducing neuroplastic changes that persist long after stimulation. Evidence of stimulation-locked neural changes would enable closed-loop application of TUS, but such responses have not yet been clearly dissociated from the coincident neural response to auditory and peripheral stimulation associated with TUS. We leveraged the contralateral retinotopic organization of the early visual cortex to isolate online TUS effects from peripheral confounds in 19 subjects. Using a hemifield visual stimulation paradigm combined with high-precision, functional MRI guided TUS, we applied TUS to the left early visual cortex while participants viewed checkerboards presented in the left or right visual field. TUS was delivered randomly on half of the trials, enabling within-subject comparisons of pattern-locked visual evoked potentials (VEPs) across hemispheres and against no stimuli. We observed a reduction in VEPs in the contralateral, but not ipsilateral, hemifield, consistent with genuine online neuromodulatory effects. Furthermore, online suppression was positively correlated with the TUS dose delivered to the target, as estimated by modelling TUS field-target overlap and differential attenuation through heterogeneous skulls. Collectively, these findings provide a robust framework for future studies aiming to map the TUS parameter space in real time by leveraging topographic organization to control for peripheral confounds.