Scientists at UC Berkeley have built a tiny, wireless sensor that might someday be able to monitor muscles or organs in real time, stimulate nerves to treat diseases, or allow people to control prosthetics with their minds.

The sensor is a 1-millimeter cube, about the size of a grain of sand. Researchers implanted them in the muscles and peripheral nerves of rats to record electrical activity, which provides information about how the nervous system is functioning in actual time. The research was published this month in Neuron.

One of the major problems in neurotechnology has been figuring out how to make durable and unobtrusive  implants that  can record and stimulate nerves. There are electrodes that connect a human brain to a prosthetic, such as a robotic arm, but they are cumbersome and have not been engineered to last for decades.

"We thought what if we could build really tiny things," says lead author Michel Maharbiz, professor of Electrical Engineering and Computer Sciences (EECS) at UC Berkeley, "untethered, no wires—and put them into your body, literally a little cube of sand could be put into your body, right next to the neuron that you cared about, and we could talk to it from the outside, without any wires or anything—then that would be a step towards solving  [the problem]."

The 'Aha' Moment

The first breakthrough, Maharbiz says, is that he and his colleagues, including Jose Carmena,  a world leader in brain-machine interfaces, turned to ultrasound and not  radio waves as a means of reading the electrical signals deep in the body. It's similar to how scientists use sonar to explore the depths of the ocean.

Ultrasound loses far less power in the body's tissues and scatters far less than radio waves. That means ultrasonic energy can penetrate more deeply at a given power, and less energy gets introduced into tissues where it's not wanted.

Here's the video UC Berkeley produced to explain "neural dust":

"For objects that are smaller than a millimeter, communicating with [radio waves] deep in the body is very difficult," Maharbiz says. "It's essentially a losing proposition, because your body is salt water, effectively, and absorbs all of that energy [that then]  gets lost in your body."

The next big breakthrough for the research team was to get the sensor device, no bigger than a speck of dust, to work in a actual organism, by implanting it next to a peripheral nerve in a rat.

"The trick is, we put this little [sensor]  in [the rat], we hit it with ultrasound and what reflects back is telling us what the neuron nearby is doing," says Maharbiz.

Because of its small size and durability, neural dust may have promise, Maharbiz says, to improve treatments for  human diseases such as epilepsy and disabilities such as tetraplegia.

What's in a Name?

Coined by Maharbiz, the term "neural dust" pays homage to work done 20 years ago by Kristofer Pister, another professor at EECS. Pister is the inventor and key implementer of something called Smartdust, which is a term that describes a collection of wireless microelectomechanical sensors that can detect everything from light to vibrations using radio waves.

Maharbiz laughs softly as he reminisces about the term "smart dust" making it "into lots of science fiction books about [how] our future was going to have all these tiny sensors everywhere in the world and they would be taking data and communicating."

Now in a world of activity trackers and neural dust,  it seems that future may not be so far away.