Low-intensity focused ultrasound pulsation along the anterior-posterior thalamic axis differentially modulates the latency of reporting conscious visual experience

Abstract

Background: Transcranial low-intensity focused ultrasound (LIFU) neuromodulation can alter human task performance depending on target and acoustic configurations. However, single behavioral endpoints cannot locate effects within multistep tasks, and predefined target labels ignore acoustic variations. Objective: To determine whether thalamic LIFU affects visual categorization or subsequent subjective report latency and whether the effects vary with target, acoustic parameter, and beam location. Methods: Sixty healthy adults were randomized to 70% or 5% duty cycle (DC70 or DC5) and received sonication on four left thalamic targets with matched pulse repetition frequency (10 Hz) and temporal-average intensity (0.72 W/cm2). Behavioral models tested target-by-DC interactions in categorization (RT1) and subjective report (RT2) latencies. Spatial analyses correlated focal spot coordinates and voxel-wise intensity from 179 acoustic simulations to baseline-adjusted RT2. Results: The target-by-DC interaction was detected for RT2 but not RT1. At the ventroposterior thalamic target, adjusted RT2 was 55.9 ms longer under DC70 than DC5. More anterior focal spots shortened RT2 under DC70 but increased RT2 under DC5. Correlation between intensity and adjusted RT2 significantly differed between DC70 and DC5 in 18.8% of thalamic voxels. These voxels formed an anterior mediodorsal-motor set and a posterior pulvinar-dominant set. Conclusions: The latency of reporting conscious visual experience, but not categorization latency, was affected by thalamic LIFU. This effect varied jointly with anterior-posterior target engagement and acoustic configuration. Analyzing sequential reaction times separately and treating field variation as an anatomical variable revealed associations not fully captured by a single endpoint or predefined target labels.