Ultrasound Brain-Computer Interfaces: Not Just a One-Way Trip into the Brain

Your understanding is only partly correct. Non-invasive ultrasonic brain-computer interfaces (BCIs) aren't just about “beaming ultrasound into the skull.” A key capability also involves using functional ultrasound imaging to read brain activity. However, if your benchmark for a true BCI is “stable, real-time, high-bandwidth, bidirectional interaction suitable for long-term use,” then current non-invasive technology is still in the early research and validation phase. Calling them mature, two-way interfaces would be a stretch.

The Crucial Distinction

• Ultrasound Can “Write” to the Brain: Transcranial ultrasound stimulation (TUS), or transcranial focused ultrasound (tFUS), acts as a non-invasive neuromodulation method. It can influence neural activity in both the cortex and deeper brain regions.

• Ultrasound Can Also “Read” Brain Activity: Researchers are investigating functional ultrasound imaging to observe brain activity, discussing it as a potential reading channel for non-invasive BCIs.

• So, “Ultrasound Only Goes In, It Can't Get Information Out” Is Inaccurate: A review already discusses ultrasound brain functional imaging, ultrasound brain modulation, and EEG-based closed-loop ultrasound neuromodulation as interconnected topics.

• But “Being Able to Read” Isn't a “Mature BCI Readout”: Existing non-invasive BCIs still wrestle with performance limitations like high error rates. This is precisely why some studies use tFUS to modulate attention-related brain areas to boost the performance of a visual-motor BCI.

• Two-Way Systems Are in Experimental Stages: One report details integrating focused ultrasound stimulation with machine learning to decode brain waves in 25 subjects, achieving a bidirectional BCI function that both encodes and decodes. However, these results are better seen as research progress, not a sign of mature, market-ready capability.

A More Precise Picture

• It's true that many current ultrasound BCI applications heavily emphasize non-invasive stimulation/neuromodulation.

• It's false that all ultrasonic BCIs are one-way streets that can only send signals in and are incapable of reading intracranial information.

• It's a much more accurate judgment to say that present-day non-invasive two-way BCIs are not yet mature and still have a considerable gap to close before achieving true high-performance, real-time, bidirectional human-machine interaction.

The Short Answer

The ultrasound pathway has both “read” and “write” technology directions. Writing relies on transcranial ultrasound stimulation, while reading leans on functional ultrasound imaging or closed-loop systems combining it with signals like EEG. However, most current non-invasive BCIs aren't mature, high-performance, two-way interfaces in the full sense. They primarily exist in a phase dominated by one-way applications, with bidirectional closed-loop systems under gradual validation.