Visuomotor Transformations Are Modulated by Focused Ultrasound over Frontal Eye Field

Neuromodulation with focused ultrasound (FUS) is being widely explored as a non-invasive tool to stimulate focal brain regions because of its superior spatial resolution and coverage compared with other neuromodulation methods. The precise effects of FUS stimulation on specific regions of the brain are not yet fully understood. Here, we characterized the behavioral effects of FUS stimulation directly applied through a craniotomy over the macaque frontal eye field (FEF). In macaque monkeys making directed eye movements to perform visual search tasks with direct or arbitrary responses, focused ultrasound was applied through a craniotomy over the FEF. Saccade response times (RTs) and error rates were determined for trials without or with FUS stimulation with pulses at a peak negative pressure of either 250 or 425 kPa. Both RTs and error rates were affected by FUS. Responses toward a target located contralateral to the FUS stimulation were approximately 3 ms slower in the presence of FUS in both monkeys studied, while only one exhibited a slowing of responses for ipsilateral targets. Error rates were lower in one monkey in this study. In another search task requiring making eye movements toward a target (pro-saccades) or in the opposite direction (anti-saccades), the RT for pro-saccades increased in the presence of FUS stimulation. Our results indicate the effectiveness of FUS to modulate saccadic responses when stimulating FEF in awake, behaving non-human primates.