A range of pulses commonly used for human transcranial ultrasound stimulation are clearly audible

Differential dose responses of transcranial focused ultrasound at brain regions indicate causal interactions

“…In this study there are at least two sources of auditory frequencies in the detectable range for non-human primates (<40 kHz) [ 62 ]: the 2 kHz PRF within each sonication and the repeated square wave envelopes, which generates a wide range of frequencies. Similar sonication patterns have been reported to produce a detectable auditory effect in human studies [ 63 ]. In this study the presence of the fMRI sequence may act as a partial mask, but the ear bars used in the frame will likely reduce the environmental noise level while the FUS induced bone conduction noise will still be present.…”

Transcranial ultrasound stimulation to human middle temporal complex improves visual motion detection and modulates electrophysiological responses

“…Recent work has raised concern that previous results in both animals and humans may have been biased by an auditory signal at the PRF transmitted through the skull to the cochlear. [17][18][19][20] The audio mask that we delivered via earphones prevented participants from accurately discriminating stimulation from sham trials, or stimulation of hMT+ from the control site. Moreover, there was no evidence that the behavioural change caused by TUS correlated across participants with their performance on the stimulation detection task.…”

“…However, the validity of previous experimental results has recently been called into question by the demonstration of TUS-induced auditory stimulation that introduces both behavioural and neurophysiological confounds. [17][18][19][20] The auditory effect is likely due to direct cochlear activation by skull conducted shear waves at the ultrasound pulse repetition frequency (PRF), 19,21 but may be mitigated by simultaneous presentation through earphones of a…”

Ramped V1 transcranial ultrasonic stimulation modulates but does not evoke visual evoked potentials

“…Early work in humans suggests that TUS can both evoke neural activity (1) and modulate activity elicited by other stimuli (2). However, the protocols used in these studies may be audible due to the sharp onset and offset of ultrasound energy (3,4), and it is therefore possible that there is an auditory confound to the observed effects (5). Here, therefore, we used a less audible, ramped protocol (3) to determine if we could either evoke or modulate activity in the primary visual cortex (V1).…”

“…As described in our previous paper (3), TUS was delivered using a 2-element spherically focusing annular array transducer (H115-2AA, Sonic Concepts) with a nominal outer aperture diameter and radius of curvature of 64mm. The transducer was driven at 270 kHz by a 2-channel TPO (Sonic Concepts) with the output power and element phase adjusted to give a focal pressure in water of 700 kPa (spatial peak pulse average intensity without ramping of 16 W/cm 2 ) and a focal distance of 43 mm.…”