Scientists still don’t know how the brain turns physical activity into thoughts, feelings, and awareness—but a powerful new tool may help crack the mystery. Researchers at MIT are exploring transcranial focused ultrasound, a noninvasive technology that can precisely stimulate deep regions of the brain that were previously off-limits. In a new “roadmap” paper, they explain how this method could finally let scientists test cause-and-effect in consciousness research, not just observe correlations.