Sound Waves Give San Diego Neuroscientists Control Over Brain Cells
You ever get the feeling sounds are controlling your mind? Maybe a catchy song gets stuck in your head. Or a noisy neighbor won't stop driving you nuts.
Well, sounds may not literally control your mind. But in the field of neuroscience, a new technique is actually giving researchers the power to control specific brain cells using sound waves.
Don't reach for a tinfoil hat just yet. So far, sound control only works on very small brains.
"So let me zoom in," says Salk Institute neuroscientist Sreekanth Chalasani as he pulls up a magnified view of the tiny C. elegans worm. "It's only a millimeter long, from head to tail."
This little worm has just about 300 neurons, and researchers know exactly what many of them do. Now, Chalasani and his colleagues have invented a way to turn on specific worm neurons using sound waves.
"We cannot hear these sound waves," Chalasani said. "They are much higher frequency than what our ears can hear."
They're ultrasound waves, the same kind used in many routine medical procedures.
People may be most familiar with ultrasound from sonograms women get throughout their pregnancies, Chalasani said.
"My sister just had a baby last month," he said. "I would see these little printouts. And those are printouts obtained from a medical ultrasound. The doctor would use an ultrasound transducer and take a picture of what my niece was doing at that particular second in time and space."
Ultrasound is useful because it moves through the body, and Chalasani's team discovered that at certain frequencies, it can activate a protein inside worms. Through genetic modification, they were able to graft that protein onto whatever worm neuron they wanted.
That gave them a kind of switch. They can now use ultrasound to flip that switch and change the worm's behavior. A video from his latest study shows one worm doing a complete 180-degree turn.
"This animal is crawling forward," Chalasani said, narrating the video.
"As soon as the ultrasound hits the worm, the neuron turns on. And when the neuron becomes active, it is telling the rest of the neural circuit, 'Hey, I've become active.' When that information passes along, the animal then turns, goes back, and goes off in a different direction."
The researchers call this technique sonogenetics. They say it will allow neuroscientists to do experiments not possible before.
Sonogenetics is a bit of a twist on another technique called optogenetics. That approach uses light to trigger specific neurons, and it was a major breakthrough when it first came out about 10 years ago.
But Chalasani said optogenetics has some limitations.
"Light does not go through skin," he said. "Light gets scattered by tissues inside the skin, as well. So you have to get pretty close to where you want to turn the cells on."
That means surgery. Mice outfitted for optogenetics often have fiber optic cables sticking out of their skulls.
"Ultrasound, on the other hand, can go through skin," Chalasani said.
Therapeutic applications for sonogenetics are a long way off, but Chalasani hopes one day ultrasound could help treat human diseases.
He points to a surgical procedure that's already benefitting Parkinson's patients by stimulating cells deep within the brain. He thinks, maybe ultrasound could deliver the same result without requiring surgery.
"Our hope would be that sticking a little ultrasound transducer outside of their brain would be enough to turn on those cells," Chalasani said.
Of course, sonogenetics has its own limitations. It'll take a lot of R&D to prove this could work on mice, let alone humans. Chalasani said one of the first steps will be to 3D-print miniature caps for the mice that will hold small ultrasound transducers right up to the animals' skulls.
As for people, Chalasani said the ultrasound-sensitive protein found in worms doesn't exist in humans. And even if scientists do find a similar switch in the human brain, they'll be hard pressed to identify which of our 86 billion neurons to target for any desired behavior.
That's why Chalasani said he's not worried about anyone abusing sonogenetics.
"There are a lot of reasons why this isn't mind control and this wouldn't work in a human right now," he said.
But if you happen to be a worm at the Salk Institute, now might be a good time to crawl into a sound-proof booth.