Sound waves activate brain cells in a worm

For the first time, scientists have directly controlled brain cells using sound waves, in a tiny laboratory worm.

They used ultrasound to trigger activity in specific neurons, causing the worms to change direction.
As well as requiring a particular gene to be expressed in the brain cells, the technique bathes the animals in tiny bubbles to amplify the sound waves.


These complications temper the technique's promise for controlling brain activity in a non-invasive way.
Writing in the journal Nature Communications, the researchers argue that their new method for controlling brain cells could improve on "optogenetics", a technique that uses light rather than sound.

The problem with light is that it cannot penetrate through tissues - it is scattered very quickly. Consequently, using optogenetics to control brain circuits in a mammal currently requires a fibre-optic implant.

By contrast, ultrasound travels relatively unimpeded through the body; this is the property that makes it useful for medical sonograms.

"This could be a big advantage when you want to stimulate a region deep in the brain," said the study's first author Stuart Ibsen, from the Salk Institute for Biological Studies in California.

Dr Ibsen and his colleagues hope to capitalise on this advantage, and their next aim is experiments in mice.

"The real prize will be to see whether this could work in a mammalian brain," said Dr Sreekanth Chalasani, who runs the lab behind the work.

For now, the team's research relies on the worm Caenorhabditis elegans, a well-studied critter with precisely 302 neurons.

Those neurons responded to the ultrasound waves thanks to a type of channel on their surface, called TRP-4, which opens when the cell membrane is stretched - such as by the incoming ultrasound wave.