Focused ultrasound for the brain

In plain language

Ultrasound is sound at frequencies too high for people to hear. When many sound waves are aimed so that they meet at one small spot, the energy at that spot can be strong enough to heat or push on the tissue there, while the surrounding tissue is largely spared.

At high intensity, this effect is used to destroy a small area deep in the brain without surgery, and an approved device treats medication-resistant essential tremor this way. At low intensity, researchers use the same kind of focus to change how active a brain region is for a short time. Early human studies report changes in movement and sensory responses, but the direction of the effect depends on the settings used, and researchers do not yet fully understand how it works.

Technical explanation

Transcranial focused ultrasound (tFUS) uses an array of transducers, usually guided by MRI, to focus acoustic energy on a target through the skull. High-intensity MR-guided focused ultrasound (MRgFUS) produces thermal lesions and is the basis of Insightec's Exablate Neuro system, which the FDA approved for medication-refractory essential tremor. The pivotal sham-controlled study enrolled 76 people (56 treated, 20 sham). Tremor scores improved by 46.9% at three months, and the treated group kept a 40% improvement at one year.

Low-intensity tFUS is studied for neuromodulation. A 2025 systematic review of 74 articles on human studies (Ho and colleagues) found that the effects depend on the stimulation settings and the target. Most motor studies used 0.5 MHz. Online suppression of motor-evoked potentials was most consistent at a 1 kHz pulse repetition frequency, a 30 to 36 per cent duty cycle and 0.4 to 0.5 second pulse trains. Theta-burst protocols at 5 Hz increased motor-evoked potentials, with an offline effect lasting about 30 minutes after sonication, extended to about 90 minutes when preceded by repetitive TMS. In the insula and dorsal anterior cingulate cortex, a 36 per cent duty cycle reduced thermal pain ratings in some studies, but the thalamus studies used other duty cycles. Some studies found no effect.

The mechanisms are incompletely understood. The review cites two proposed models, neuronal intramembrane cavitation and mechanosensitive ion channels, and it notes that auditory confounds remain a concern in sham-controlled work. A medRxiv preprint of a dose-escalation study in ten healthy adults, targeting the right amygdala with four parameter sets, reported no adverse events and no significant overall effect on affective measures. The preprint is cited here as checked. A later peer-reviewed version was published in Neuromodulation.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• The only approved uses in the sources reviewed are high-intensity ablation for essential tremor and, as Practical Neurology reports, drug-refractory Parkinson disease (2021). Low-intensity neuromodulation has no approved indication in these sources.
• Results are inconsistent. Some studies find no effect, and whether the effect is excitatory or inhibitory depends on frequency, duty cycle, pulse duration and target region (Ho and colleagues, 2025).
• Mechanisms are incompletely understood, and auditory confounds remain a concern for sham-controlled studies (Ho and colleagues, 2025).
• The dose-escalation preprint in ten healthy adults found no significant overall effect on affective measures, so its findings are preliminary (Spivak and colleagues, 2025).

Possible future uses

Timeline

1. 2021Practical Neurology reports that Exablate Neuro was previously approved for drug-refractory Parkinson disease. Sources: [2]
2. 29 Oct 2025A medRxiv preprint reports a dose-escalation study of amygdalar tFUS in ten healthy adults, with no adverse events reported. Sources: [3]
3. 28 Nov 2025A systematic review of 74 articles on low-intensity tFUS in humans is published in the Journal of NeuroEngineering and Rehabilitation. Sources: [1]

Futures this could help bring about

How far away?

Treating severe depression in days with brain stimulation

Pilots · 7 of 9 steps done

Related breakthroughs

• Low-intensity focused ultrasound to the amygdala changes brain activity and reduces distress symptoms in an early human study (24 Apr 2025)
• Focused ultrasound to left prefrontal cortex eased depression scores versus sham in small trial (8 Aug 2024)

Glossary

Transcranial

Passing through the skull, so that energy or signals reach the brain without surgery.

Neuromodulation

Changing the activity of nerve circuits, for example by stimulation, without destroying tissue.

Duty cycle

The fraction of time during which ultrasound is switched on within each pulse train.

Motor-evoked potential

An electrical response in a muscle, recorded after the motor cortex is stimulated, used to measure how excitable the motor system is.

Sources

1. review article
   Neuromodulation effects of low-intensity transcranial focused ultrasound in human, a systematic review focusing on motor and sensory functions
   Heng-Chen Ho, Wen-Shiang Chen, Ming-Yen Hsiao. Journal of NeuroEngineering and Rehabilitation, 28 Nov 2025. DOI: 10.1186/s12984-025-01722-9. Accessed 21 Oct 2026.
2. news
   The FDA Has Approved a Focused Ultrasound Device for Essential Tremor
   Practical Neurology, 11 Jul 2025. Accessed 21 Oct 2026.
3. preprint
   Dose-Escalation Study of Amygdalar Transcranial Focused Ultrasound in Healthy Volunteers
   Norman M. Spivak. medRxiv, 29 Oct 2025. DOI: 10.1101/2025.10.21.25338018. Accessed 21 Oct 2026.
4. company announcement
   FDA approves Exablate Neuro Focused Ultrasound
   Insightec, 2025. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.