Off-target auditory confound

A critical confound in ultrasonic neuromodulation experiments: pulsed ultrasound generates audible frequencies (through envelope modulation and skull vibration) that can activate the auditory pathway, producing a startle-like sensorimotor response that mimics direct neural excitation. Rodent studies demonstrated that much of the apparent motor-cortex activation by focused ultrasound was in fact mediated by this indirect auditory route, and was abolished by deafening or by smoothing the pulse envelope.

The lesson raised the field's standards: credible tFUS claims now require controls such as auditory masking, smoothed or randomised envelopes, deaf-animal or brainstem-lesion controls, and careful matching of somatosensory and startle cues. It is the paradigm case of why intellectual honesty and rigorous sham design are indispensable in acoustic neurotechnology.