Focused ultrasound neuromodulation

Low-intensity focused ultrasound (FUS) can modulate neural activity noninvasively with millimeter-scale focal spots that can be steered to deep brain structures, a spatial advantage over TMS and transcranial electrical stimulation, whose fields are broad and superficial. Ultrasound at these intensities is thought to act largely by mechanical means, deforming mechanosensitive channels and altering membrane capacitance, rather than by heating.

A serious confound in animal and human studies is indirect auditory activation: the pulsed beam can produce an audible or cochlear-transduced signal that itself drives brain responses, so effects must be controlled against this artifact. Low-intensity FUS neuromodulation should not be confused with high-intensity focused ultrasound (HIFU) thermal ablation, an established therapy that permanently lesions a target (for example the VIM for essential tremor). Human low-intensity neuromodulation is early stage, with dose-response relationships and mechanism still unsettled.