Exploring the Potential of Transcranial Ultrasonic Stimulation: A New Non-Invasive Approach to Modulating Neural Activity

Transcranial ultrasonic stimulation (TUS) is an innovative and non-invasive method of brain stimulation that offers a higher spatial resolution than traditional electrical and magnetic stimulation techniques. Additionally, TUS has the unique ability to target deep brain structures. Early studies in humans have shown that TUS can evoke neural activity as well as modulate activity elicited by other stimuli. However, the protocols used in these studies may be audible due to the sharp onset and offset of ultrasound energy, which raises concerns about the potential for an auditory confound to the observed effects.

To further investigate the effects of TUS, a group of researchers at Johannes Gutenberg University Medical Center and University College London (UCL) used a less audible, ramped protocol to determine if they could either evoke or modulate activity in the primary visual cortex (V1). In their study, 14 healthy participants (4 female, 31 ± 4.3 years) were included, and the project was approved by the UCL research ethics committee.

The 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/cm2) and a focal distance of 43 mm. The measured -3 dB focal size in water was 5 mm (lateral) by 30 mm (axial). Ramped pulses (1 ms Tukey ramp, 3.25 ms total pulse duration) were applied at a pulse repetition frequency (PRF)

Key points

• In this study, a less audible ramped protocol was used to examine whether TUS alone can evoke neural activity in the primary visual cortex (V1) and whether it can modulate visual evoked potentials (VEPs) in response to a pattern-reversal checkerboard stimulus
• 14 healthy participants were included in the study and EEG was recorded from 16 channels
• The results showed that TUS alone did not evoke any potentials and there was no significant difference between real and sham TUS conditions, but TUS did modulate the N75 component of the VEP, which likely originates in V1
• The study suggests that TUS can be a useful tool for studying the physiological basis of visual perception and for modulating neural activity in basic science and clinical applications, but replication studies are needed to draw definitive conclusions.

Reference Paper

Nandi, T. et al. (2023) “Ramped V1 transcranial ultrasonic stimulation modulates but does not evoke visual evoked potentials,” Brain Stimulation, 16(2), pp. 553–555. Available at: https://doi.org/10.1016/j.brs.2023.02.004.

To learn more about transcranial ultrasound stimulation, visit our techniques page or visit the Brainbox Initiative for workshops and webinars