Turning certain brain cells on and off with light — a technique called optogenetics — is one of the most important tools in neuroscience. It allows scientists to test basic ideas about how brains work. But because waves of visible light don’t penetrate living tissue well, the technique requires the insertion of a conduit for the light into the brain — a very thin fiber optic cable.

For the first time, researchers say, they have done the same with ultrasound, opening the way to a noninvasive way to probe the functions of neurons. They call the technique sonogenetics. They achieved this in a microscopic worm, a creature so simple that it doesn’t have a brain. But it does have neurons, which have a great deal in common with the neurons in more complex animals that make up the brain and nervous system. If the technique works in more complex animals, it would mean a noninvasive way to do basic research, and perhaps even treat brain circuits.

“Previous studies have shown if you use ultrasound, you can manipulate the nervous system,” said Sreekanth H. Chalasani of the Salk Institute in San Diego and senior author of a recent report in Nature Communications that describes the research. But, he said, nobody had shown that, with genetic modifications, specific neurons could be targeted.

“It’s going to be a viable technique,” said William Tyler, a neuroscientist at Arizona State University, who said the ability to zero in on one neuron or a group of neurons without having to insert anything into the body was “unparalleled.”