The ability to control brain cells with sound waves sounds like science fiction, right? A group of scientists in California have done just that. By using genetically modified neurons coupled with microbubbles, the researchers have demonstrated they can control the movements of nematodes. The process – called sonogenetics – uses sound waves to turn neurons on and off. The study is published in the journal Nature Communications, and details how sound waves can target brain, heart, and muscle cells to control movement.
A similar technique, called optogenetics, is currently in practice and uses light pulses to control neurons. Just like a switch in your house turns your lights on and off, light can be used to turn neurons on and off. Special light-sensitive channel proteins are added to specific neurons, and are then activated with focused lasers. However, the procedure gets tricky when it comes to cells deep inside the body. The brain and other tissue can get in the way, scattering the light, and in order to reach certain cells, an optical fiber is surgically implanted. Sonogenetics is less invasive as low-frequency sound waves can pass through tissue and bone with ease.
Sreekanth Chalasani of the Salk Institute for Biological Studies and lead author said, “In contrast to light, low-frequency ultrasound can travel through the body without any scattering. Light-based techniques are great for some uses and I think we're going to continue to see developments on that front. But this is a new, additional tool to manipulate neurons and other cells in the body."
Chalasani and his team conducted their research on nematodes, a type of roundworm. Typically, the worms don’t respond to ultrasound, but with the addition of a bubble-filled fluid, everything changed. As part of the experiment, the worms were surrounded by fluid containing tiny gas-filled bubbles. Low-intensity ultrasound waves – the same type used in sonography – were amplified by the bubbles before propagating into the worms.
The sound waves target specific structures – known as TRP-4 channels – within the membranes of certain nematode cells. By opening up the TRP-4 channels, the corresponding cells activate and respond to sound waves. In the experiment, Chalasani genetically modified the nematodes’ cells to carry the TRP-4 channels and as a result showed the neurons could be controlled by ultrasound.
So far, the work has only been performed on worms. The team is confident the technique can be carried out on any animal, with the ultimate goal of using this technique to treat humans. "The real prize will be to see whether this could work in a mammalian brain," Chalasani says in a statement. His group has already begun testing the approach in mice. "When we make the leap into therapies for humans, I think we have a better shot with noninvasive sonogenetics approaches than with optogenetics."
Chalasani told the Guardian, “We believe that, using gene therapy and a therapeutic virus, it may be possible to make target human neurons temporarily susceptible to the ultrasound signal in a clinical setting for certain neurological treatments." He added that other possible applications could focus on muscle and insulin-producing cells.
Researchers hope the procedure could one day be used to treat symptoms of degenerative diseases such as Parkinson’s, as it is minimally invasive and allows the treatment to be focused on specific areas of the brain without affecting other regions. Current treatments rely on electrical pulses to stimulate the brain, and are very invasive.