Focused Ultrasound Neuromodulation of the Central Lateral Thalamus in a Non-Human Primate Model of Disorders of Consciousness

Objectives: Disorders of consciousness (DOC) affect an estimated 200,000 patients in the United States. Effective treatment options have remained elusive. Focused ultrasound neuromodulation (FUS) of brain regions controlling consciousness, such as the central lateral thalamus (CLT), has emerged as a promising non-invasive treatment. However, prior studies have been limited by broad effective stimulation volumes, missing control conditions, and limited target validation. This study investigated the effects of FUS of the CLT in a non-human primate model of DOC with robust control conditions and more robust targeting than previous experiments. Materials and Methods: Two male rhesus macaques underwent 1-hour propofol anesthesia sessions as a model of DOC. Bilateral CLT targets were sonicated using a stereotactically mounted 256-element phased-array focused ultrasound system. Focused and unfocused (random phases) paradigms were tested in both animals, and a spotlighting (sonicating multiple targets) paradigm was tested in one animal. Arousal was monitored via EEG beta power, pulse oximetry, breathing rate, and movement, and compared between sonication and control sessions for each paradigm. Results: Paired Wilcoxon signed-rank tests showed no significant differences for any of the four measures across the three paradigms (all pFDR [≥] 0.30). The largest observed effect was increased body movement under the unfocused paradigm (rrb = +0.58), though this did not reach statistical significance. Animals remained physiologically stable throughout sessions and recovery periods, with no clinically significant changes in heart rate, breathing rate, blood oxygen saturation, or other safety concerns. Conclusions: Under the tested parameters, FUS of the CLT did not produce measurable changes in arousal. The absence of adverse physiological effects supports the safety of this FUS paradigm. The largest effect occurring under spatially distributed sonication, consistent with prior evidence that broader stimulation volumes produce stronger arousal responses, suggests that distributed network stimulation may warrant investigation as an alternative to focal targeting. Future studies should investigate this possibility and should include robust control conditions to properly quantify effects.