Unilateral online ultrasound stimulation of early visual cortex suppresses responses to contralateral visual stimuli
Suraya Dunsford, Keith Murphy, Ema Darrieutort, Elsa Fouragnan, Giorgio Ganis
Brain Stimulation 2026, 19, 103023 · 10.1016/j.brs.2025.103023
Abstract
Introduction Transcranial ultrasound stimulation (TUS) shows great promise for inducing neuroplastic changes that persist long after stimulation. Evidence of stimulation-locked (online) neural changes would enable the development of closed-loop application of TUS. However, such responses have been difficult to distinguish from coincident neural activity caused by auditory and somatosensory effects of TUS. Methods To dissociate genuine online neuromodulatory effects from peripheral confounds, we leveraged the contralateral retinotopic organization of the early visual cortex in nineteen 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 hemifield. Randomized delivery of TUS on half of the trials enabled within-subject comparisons of hemisphere-specific, pattern-locked visual evoked potentials (VEPs) across stimulated and unstimulated hemispheres, as well as across visual-stimulus and no-stimulus conditions. Results TUS to the left visual cortex reduced mean VEP amplitude over the stimulated (left) hemisphere for right-hemifield (contralateral) stimuli. No such reduction appeared at the symmetric right-hemisphere sites for left-hemifield stimuli. The degree of online suppression correlated positively with target engagement, estimated by modelling the TUS field that accounted for inter-individual heterogeneity in skull transmission and its overlap with the fMRI-defined target. This relationship suggests that greater target engagement is reliably associated with stronger TUS-induced neural modulation. Conclusions These findings provide clear evidence of online, spatially specific TUS-induced neural modulation, dissociated from peripheral confounds. This approach establishes 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, and supports the development of closed-loop neuromodulation protocols.
Abstract via europepmc.
Exposures
Exposure 1: Online TUS to left early visual cortex during hemifield visual stimulation
Target: primary visual cortex — “left early visual cortex (calcarine sulcus)”
Device: NeuroFUS · Sonic Concepts (sold by Brainbox) · NeuroFUS TPO system ✓
| Waveform | continuous | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | not applicable | |
| Pulse repetition frequency (Hz) | not applicable | |
| Duty cycle (%) | 100 | ✓✓✓ |
| Sonication duration (s) | 0.5 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 40 | ✓✓✓ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | simulationmean or range across subjects | |
| In-situ pressure (kPa) | 310 | ✓✓✓⚑ |
| In-situ Isppa (W/cm²) | 3.9 | ✓✓✓ |
| In-situ Ispta (W/cm²) | not reported |
Each trial consisted of a single 500 ms continuous-wave pulse, time-locked to begin 400 ms before a 20-ms checkerboard visual stimulus. Each block comprised 100 trials (50 stimulation, 50 no-stimulation, alternating) with a 4.0 s inter-trial interval; 5 blocks were administered per session.
Flags from extraction
randomised— Paper does not state whether stimulation vs. no-stimulation trial order was formally randomized (described as alternating within blocks); left as not_reported.blinding— Paper does not describe participant or experimenter blinding to TUS vs. no-stimulation trials; not stated.sham_type— Study used a within-subject no-stimulation (NoS) control condition rather than a sham/placebo transducer condition; classified as sham_type none since there was no separate sham arm, only active-vs-no-stimulation trials.exposures[0].in_situ.pressure_kpa— Table 1 ROI-mask row reports mean pressure across participants at the functionally defined target (0.31±0.09 MPa); recorded as the mean per the mean±SD convention.