Researchers affiliated with MIT argue that transcranial focused ultrasound—a noninvasive technique that can modulate activity in deep brain regions—could enable more direct, cause-and-effect tests of how conscious experiences arise. In a “roadmap” review in *Neuroscience & Biobehavioral Reviews*, they describe experimental approaches aimed at distinguishing between competing accounts of where and how awareness is generated in the brain.
Consciousness remains a central unresolved problem in neuroscience and philosophy: researchers can measure brain activity linked to experience, but establishing whether a given signal causes a conscious percept, rather than merely accompanying it, is far harder.
A review article in Neuroscience & Biobehavioral Reviews proposes that transcranial focused ultrasound (tFUS) could help close that gap by allowing researchers to modulate activity in specific brain regions without surgery, including targets deep beneath the cortex. The authors describe the method as capable of concentrating acoustic energy onto a small, millimeter-scale target through the skull, offering access to subcortical structures that are difficult to influence with noninvasive techniques such as transcranial magnetic stimulation or transcranial electrical stimulation.
The paper—“Transcranial focused ultrasound for identifying the neural substrate of conscious perception”—lists Daniel K. Freeman, Brian Odegaard (University of Florida), Seung-Schik Yoo (Brigham and Women’s Hospital and Harvard Medical School), and Matthias Michel (MIT) as authors.
Freeman, a researcher at MIT Lincoln Laboratory, said the approach could broaden what is experimentally possible in healthy volunteers. “Transcranial focused ultrasound will let you stimulate different parts of the brain in healthy subjects, in ways you just couldn't before,” he said, arguing that it could be used not only for medical and basic-science questions but also to probe long-standing debates about the “hard problem of consciousness.”
Michel, a philosopher who studies consciousness, emphasized that a major bottleneck in the field is the limited set of tools that can safely and reliably manipulate brain activity. “There are very few reliable ways of manipulating brain activity that are safe but also work,” he said.
In outlining research directions, the authors point to how stimulation experiments could help separate neural activity that is essential for conscious perception from activity that may be downstream or incidental. They frame the opportunity as a way to test broad families of views often discussed in the consciousness literature, including accounts that emphasize higher-level integration—commonly associated with the frontal cortex—and accounts that place more weight on localized or lower-level processes, potentially including subcortical contributions.
The paper also highlights pain and vision as candidate domains for early work, in part because behavioral responses can sometimes precede a person’s reported experience, raising questions about where conscious sensation is generated. Freeman described that uncertainty as a basic scientific gap: “It's a basic science question, how is pain generated in the brain,” he said, adding that researchers still debate whether key components of pain experience depend mainly on cortical regions or deeper structures.
Freeman and Michel said they are planning experiments that begin with stimulation of the visual cortex and later extend to higher-level frontal regions, with the goal of relating induced neural changes to what a participant actually experiences. Freeman summarized the distinction as moving from neural signals alone to subjective report: “It's one thing to say if these neurons responded electrically. It's another thing to say if a person saw light,” he said.
Beyond the review, Michel and neuroscientist Earl Miller co-lead the MIT Consciousness Club, an interdisciplinary forum that hosts regular events on consciousness research. MIT has described the club as supported by a grant from the MIT Human Insight Collaborative (MITHIC).
The research described in the review was supported by the U.S. Department of the Air Force, according to MIT’s published account of the work. Michel cautioned that the method is still emerging as a research tool, saying, “It's a new tool, so we don't really know to what extent it's going to work,” while arguing the approach is “low risk and high reward.”
