Technical Basis

Functional ultrasound (fUS) applies high-frequency ultrasound pulses to measure blood flow changes reflecting neural activity, analogous to functional MRI but using ultrasound instead of magnetic resonance. The approach detects microvasculature blood flow changes that correlate with local neural population firing, enabling spatial mapping of brain activity.

Spatial and Temporal Resolution

fUS achieves 2-10 Hz temporal resolution, substantially slower than intracortical recordings (kilohertz) but faster than fMRI (0.5 Hz). Spatial resolution is approximately 100 micrometers, intermediate between EEG and intracortical approaches. This resolution-speed tradeoff suits many BCI applications while maintaining completely noninvasive recording.

Advantages Over Implants

The fundamental advantage of fUS is that no surgical implantation is required. Ultrasound transducers can be positioned on the scalp similar to EEG electrodes, eliminating infection risks, surgical complications, and chronic inflammatory responses. This noninvasive property could enable widespread BCI adoption if functional decoding capability proves sufficient.

Current Development Status

Merge Labs and other companies are advancing fUS toward human BCI applications, leveraging foundational research demonstrating motor intention decoding in animal models. Gestala and other research groups are exploring fUS combined with deep learning for improved decoding accuracy.

Fundamental Limitations

fUS shares fundamental limitations with other hemodynamic approaches: recording lags neural firing by several seconds due to neurovascular coupling kinetics, and spatial resolution remains coarser than direct electrical recording. Despite limitations, the noninvasive property positions fUS as a promising long-term BCI pathway.