New brain-stimulation tool may finally reveal how consciousness works

For decades, neuroscientists have watched brain activity light up on screens while people see, feel, and think — but they couldn't tell whether those signals created consciousness or just followed it. That gap between observation and causation may be closing.

Two MIT researchers have published a roadmap for using transcranial focused ultrasound — a technology that's been around for years but rarely applied to consciousness research — to directly stimulate specific brain regions and watch what happens. The technique sends focused acoustic waves through the skull to activate neurons deep inside the brain, in areas previously accessible only during surgery.

"It truly is the first time in history that one can modulate activity deep in the brain, centimeters from the scalp, examining subcortical structures with high spatial resolution," says Daniel Freeman, one of the MIT researchers leading the effort. "There's a lot of interesting emotional circuits that are deep in the brain, but until now you couldn't manipulate them outside of the operating room."

Moving from watching to testing

The difference sounds subtle but matters enormously. Current brain imaging — MRI scans, EEG recordings — shows correlations. They reveal which regions light up when you see red or feel pain. But correlation isn't causation. A brain signal could be generating the experience, reflecting it, or just happening nearby.

By directly stimulating a specific brain area and asking a person what they experience, researchers can finally establish cause and effect. If stimulating region X causes someone to see light, or feel pressure, then region X is actually necessary for that experience. That's the kind of answer consciousness research has been missing.

The roadmap targets two competing theories of how consciousness works. The "cognitivist" view holds that conscious experience requires high-level mental processing — reasoning, self-reflection, integration across brain regions. This view points to the frontal cortex as central. The "non-cognitivist" alternative suggests consciousness emerges from simpler, more localized neural patterns, possibly in the back of the brain or deeper structures, without needing elaborate interpretive machinery.

These aren't abstract philosophical debates. They lead to concrete, testable predictions. If the cognitivist view is right, disrupting communication between distant brain regions should disrupt consciousness. If the non-cognitivist view is right, stimulating a small, localized area should produce specific conscious experiences.

What comes next

Freeman and his colleague Matthias Michel aren't just publishing theory. They're already designing experiments, starting with the visual cortex. They'll stimulate these regions in healthy volunteers while recording what people actually report seeing — building a causal map of visual perception rather than just a picture of which neurons respond to light.

The same approach applies to pain, another fundamental conscious experience where basic questions remain unanswered. Does pain originate in cortical areas near the brain's surface, or in deeper structures? "It's surprising there is such uncertainty," Freeman says. "Now we have a tool to examine it."

Michel has also co-founded the MIT Consciousness Club, a cross-disciplinary group aiming to accelerate consciousness research across Boston-area institutions. The momentum is building — not because consciousness suddenly became easier to study, but because, for the first time, researchers have a way to move beyond watching and start asking the brain directly: what are you actually doing when I think, feel, or see.

Study: "Transcranial focused ultrasound for identifying the neural substrate of conscious perception" — Neuroscience & Biobehavioral Reviews, 2025