Nucleus-Specific Transcranial Ultrasound Stimulation of the Thalamus: Testing Dissociable Effects on Perceptual Awareness and Motor Control

Abstract

This project investigates whether transcranial ultrasound stimulation (TUS) can produce target-specific modulation of distinct thalamic nuclei involved in perceptual awareness and motor control. TUS is a non-invasive neuromodulation technique capable of reaching deep brain structures with greater spatial precision than many conventional stimulation methods, making it a promising approach for investigating thalamic function. However, the extent to which TUS can selectively target neighbouring thalamic nuclei and produce functionally specific behavioural effects remains unclear. Healthy participants complete MRI scanning to enable individualised anatomical targeting and acoustic simulation prior to stimulation. In separate stimulation sessions, TUS is delivered to the mediodorsal (MD) and ventrolateral (VL) thalamic nuclei, alongside a sham condition. Behaviour is assessed immediately before and after stimulation using two tasks designed to probe dissociable functions: a near-threshold backward-masking task assessing perceptual access and an isometric force-production task assessing motor control. Acoustic simulations are used to estimate the location, intensity and selectivity of ultrasound exposure for each participant and stimulation session. The primary aim is to test for a double dissociation in which MD stimulation selectively impairs near-threshold perceptual performance, while VL stimulation selectively impairs force-production performance, relative to the other stimulation condition and sham. Secondary analyses will examine whether individual differences in stimulation dose predict the magnitude of behavioural response. The project aims to provide evidence concerning the feasibility and functional specificity of individualised thalamic TUS, improve understanding of the respective contributions of MD and VL thalamus to awareness and motor control, and inform the development of more precise TUS targeting approaches for future translational research in disorders of consciousness.