Stimulating The Brain With High Frequency Sound Waves

Controlling brain activity using ultrasound has been a theoretical possibility that scientists have been working on for a while. The advantage over electrical stimulation is that sound can target any part of the brain, and would not involve an invasive procedure. MIT Technology Review is reporting on some of the recent advancements in the field. Here's a snippet:

One of the challenges in using ultrasound to target the brain is figuring out how to get the sound waves through the skull in a controlled manner. Typically, ultrasound operates in the megahertz to gigahertz range--frequencies that are fine for passing through soft tissue but would liquefy bone. (As bone absorbs the energy of the acoustic wave, it heats up.) Researchers at Brigham and Women's Hospital, in Boston, have found that an ultrasound frequency of less than one megahertz can do the trick, but with a trade-off: the lower the frequency, the more difficult it is to focus the energy on a particular point in the brain.

In the past year, however, scientists have had some success in solving this trade-off. Detailed images of the skull generated via CT scan and MRI can help scientists calculate the best way to focus the sound waves, says Seung-Schik Yoo, a neuroscientist at Brigham and Women's and Harvard Medical School. In as yet unpublished work, Yoo and his colleagues have demonstrated that low-frequency, low-intensity ultrasound can successfully suppress visual activity in rabbits' brains, as well as selectively trigger activity in the motor cortex. "We are also looking at the ability to modulate hormones or neurotransmitters, which may have application for psychiatric disorders, obesity, and addiction," says Yoo.