Deep within the human brain lies a structure no larger than a walnut, long associated with the tension between impulse and intention. Researchers have now shown that focused ultrasound waves, directed at this subthalamic nucleus from outside the skull, can measurably improve a person's capacity for deliberate self-control — without a single incision. Published in Nature, the finding places a non-invasive technology at the threshold of the brain's most guarded cognitive territory, raising quiet but consequential questions about what it might mean to modulate the very circuits that make us pause