# Could Sound Waves One Day Control Brain Activity? A New Study Brings Ultrasound Therapy Closer to Reality Scientists at the Salk Institute have discovered that ultrasound—the same technology used to image babies in the womb—can be used to safely and precisely activate specific brain cells in mice. By engineering mice to produce a pressure-sensitive protein called TRPA1 in particular neurons, researchers were able to trigger electrical activity and visible leg movements using targeted sound waves. This breakthrough, published in *Nature Communications*, represents an important step forward for the emerging field of **sonogenetics**, which aims to control brain circuits non-invasively. While the technique is still far from being used in humans, experts say it could one day offer a less invasive way to treat conditions like epilepsy, Parkinson's disease, and depression. # Could Sound Waves One Day Control Brain Activity? A New Study Brings Ultrasound Therapy Closer to Reality ## Table of Contents - Key Points - Why This Research Matters - The Tools Already Being Used: Light, Electricity, and Magnets - The Promise of Ultrasound - How the Research Was Conducted - Key Findings: From a "Blazing Field of Light" to Tiny Kicks - What This Means for Patients - What the Study Couldn't Prove - What Comes Next: A Roadmap for Future Research - Frequently Asked Questions - Source Information ## Key Points - Ultrasound activated specific brain cells in mice engineered to produce the pressure-sensitive protein TRPA1. - The technique, called sonogenetics, might one day help treat epilepsy, Parkinson's, or depression. - This was an animal study using direct brain injections, so human use is still far off. - Long-term effects of repeated ultrasound on brain tissue are not yet known. - Future research will focus on better proteins, silencing neurons, and non-invasive gene delivery. ## Why This Research Matters Imagine being able to turn any neuron in the brain on or off—whenever you want, and for however long you want. That's the ambitious goal of a field of research focused on precisely targeting the brain's circuits. Scientists believe this level of control could hold the key to treating a wide range of neurological conditions, including **epilepsy** (a disorder characterized by recurrent seizures), **Parkinson's disease** (a progressive movement disorder), and **depression** (a mood disorder affecting millions worldwide). This new study, led by neurobiologist **Sreekanth Chalasani** at the Salk Institute, introduces a fresh approach to that challenge. Rather than using light, electricity, or magnets—the tools that have dominated the field—the researchers turned to ultrasound. The work is the latest development in a small but rapidly growing field known as **sonogenetics**, which uses sound waves to control cells. Experts who reviewed the study are cautiously optimistic about its significance. "It's a very exciting contribution and an important step," said **Mikhail Shapiro** of Caltech, a sonogenetics expert who was not involved in the study. "This is one of the papers that's come out over the last several years that shows that it's a real possibility that you can use ultrasound to directly modulate the activity of specific neurons." ## The Tools Already Being Used: Light, Electricity, and Magnets To understand why this new study matters, it helps to know what scientists have already tried. Researchers have long known that cells can be activated with flashes of light if they carry certain light-sensitive proteins—a technique called **optogenetics**. Using optogenetics, scientists have achieved remarkable results in animals and even humans: - Researchers have used light to make mice stop, swerve, or even hallucinate - In May 2021, researchers reported that they had used optogenetics to help a blind person see again Another approach involves electrical stimulation, sometimes by implanting electrodes directly into the brain, or by using magnetic fields—a strategy known as **transcranial magnetic stimulation (TMS)**. These techniques are already being used in patients with depression, Parkinson's disease, and epilepsy. But each method has drawbacks. Light cannot travel very far through tissue, which makes optogenetics difficult to use unless you are targeting nerve cells in a clear organ like the eye. Electrical stimulation, while effective at reaching deep parts of the brain, requires surgical implants. And while transcranial magnetic stimulation is non-invasive, magnetic fields quickly weaken as they move through brain tissue, limiting how deep they can reach. ## The Promise of Ultrasound Enter ultrasound. These high-frequency sound waves are already widely used in medicine to see deep inside the body. Doctors use them to break up kidney stones, scorch tumors, and glimpse developing fetuses during pregnancy. "Everybody gets ultrasounds; things turn out to be OK," Chalasani said, highlighting the proven safety record of the technology. His team's bold question was simple: Could we find a protein that senses ultrasound? The answer, his team reported in a 2015 study, was "yes"—but at the time the experiments were done in *Caenorhabditis elegans*, a tiny, transparent nematode (roundworm) about the length of a pencil point. Researchers found that pulsing these worms with ultrasound caused them to wriggle away. However, worms with a mutation in a particular protein didn't react—a telltale sign that this molecule was essential for the ultrasound response. The question remained: Would a similar protein work in mammalian cells, which are far more complex? That's exactly what the latest study set out to answer. ## How the Research Was Conducted Chalasani's team launched an extensive search for a protein that would respond to ultrasound in mammalian cells. The process was painstaking and lengthy: 1. Researchers spent about a year and a half testing nearly **200 genes** encoding proteins known to respond to pressure 1. Each candidate protein was tested to see if it also responded to a **7-megahertz burst of ultrasound**—a frequency comparable to what is used in some medical imaging 1. Any cells that responded to the ultrasound would light up green under a microscope, giving the team a clear visual signal About five months into this effort, the researchers still hadn't found any promising candidates. It was a frustrating stretch that might have caused some teams to give up. Then, one night, something unexpected happened. Chalasani, who was in his office, heard two members of his team screaming. He went over to see what all the fuss was about—and that's when he saw it. "It wasn't an occasional thing," Chalasani said of the microscope images. "This was just like a blazing field of light." That dazzling display of green light was the result of cells producing a protein called **TRPA1**, a molecule researchers believe is usually activated by chemical irritants and toxins. It turned out to be the key to making cells responsive to ultrasound. To confirm their finding, the scientists then coaxed neurons isolated from mice into producing TRPA1. These cells started firing off electrical signals in response to ultrasound, proving the protein could make mammalian neurons ultrasound-sensitive. Finally, to see whether those findings held up in living animals, the researchers used a mouse strain that only produced TRPA1 in a specific group of **cortical motor neurons**—the cells that control voluntary muscle movements. The results were dramatic. ## Key Findings: From a "Blazing Field of Light" to Tiny Kicks The study produced several major findings that together demonstrate the potential of sonogenetics: - **TRPA1 is ultrasound-sensitive:** The protein, which normally responds to chemical irritants and toxins, also responds to mechanical pressure from ultrasound waves - **Lab-grown cells became responsive:** Neurons isolated from mice that produced TRPA1 began firing electrical signals when exposed to ultrasound - **Living mice responded too:** When the researchers pulsed mice with ultrasound, the animals showed spikes of electrical activity in their limbs and even produced small but visible movements—tiny kicks - **The effect was targeted:** Because the mouse strain only produced TRPA1 in cortical motor neurons, the ultrasound specifically affected movement-related brain circuits These results confirm that ultrasound can be used to activate specific populations of neurons deep within the brain of a living animal—something that has been difficult to achieve with light-based or magnetic approaches. "This paper is another really important piece to this puzzle of developing neural circuit-based therapeutics for disease," said **Colleen Hanlon**, a biologist at Wake Forest School of Medicine who leads research in transcranial magnetic stimulation but welcomes other approaches to regulating how neurons communicate. ## What This Means for Patients While this study was conducted in mice, its implications for human medicine are significant. The ultimate goal of this research is to develop treatments that can target brain circuits implicated in disease—without the need for invasive surgery. Conditions that might one day be treated with ultrasound-based brain stimulation include: - **Epilepsy:** By calming overactive neurons that trigger seizures - **Parkinson's disease:** By stimulating or regulating the circuits responsible for movement control - **Depression:** By modulating the neural pathways involved in mood regulation That's where the scientific findings get interesting. Dr. Chalasani plans to keep pursuing new ways to refine the technique: - **Improving sensitivity:** His team is already working on tweaking the TRPA1 protein to get stronger responses to ultrasound - **Turning neurons off:** While activating neurons is useful, Chalasani notes that it's equally important to be able to silence cells. He believes his lab may have found a protein that does just that—a molecule produced by the carnivorous **Venus flytrap** plant—but it will take careful follow-up work to confirm - **Improving gene delivery:** In this study, researchers injected mice directly into the brain with a virus that carried the TRPA1 gene. That approach is invasive, which negates one of ultrasound's main benefits. Caltech's Shapiro suggests a possible workaround: using ultrasound to temporarily weaken the **blood-brain barrier**—the protective filter that keeps many substances out of the brain—which could allow viral vectors to pass through and reach their targets without direct injection - **Studying existing proteins:** Even if researchers can't figure out how to deliver ultrasound-sensitive proteins to the brain, they might learn how to stimulate proteins that neurons already have, said Hanlon. This "chemical-free" approach could open entirely new avenues for therapy "We've spent so much time over the last few decades focusing on pharmacologic therapies," Hanlon said. "This paper is another really important piece to this puzzle of developing neural circuit-based therapeutics for disease." ## What the Study Couldn't Prove It's important to understand what this study does—and doesn't—show. The research was conducted in mice, not humans, and human brains are significantly more complex. Several critical questions remain unanswered: - **Long-term safety:** While ultrasound is generally considered safe, the effects of repeated, targeted ultrasound exposure on brain tissue over long periods are not yet known - **Delivery challenges:** The study used direct injection of a virus into the brain to deliver the TRPA1 gene—a method that would not be acceptable for routine human use. The blood-brain barrier remains a major obstacle - **Specificity in humans:** It remains unclear whether the technique would work as precisely in human brains, which are larger and have different anatomical features than mouse brains - **Turning cells off:** The study demonstrated activation of neurons, but the ability to inhibit (turn off) neurons—which is equally important for treating conditions like epilepsy—was not yet proven - **Translation timeline:** Sonogenetics still has a lot of catching up to do compared to other, more established fields like optogenetics and electrical stimulation Experts emphasize that much work remains before these tools can be used in people—from figuring out how to deliver genes encoding ultrasound-sensitive proteins to understanding exactly how the mechanical ultrasound signal becomes an electrical signal in neurons. ## What Comes Next: A Roadmap for Future Research For patients who might benefit from this technology, the path forward involves several key research priorities: 1. **Identify the best ultrasound-sensitive proteins:** TRPA1 is a promising start, but researchers will need to find or engineer proteins that are more sensitive and specific, especially for human cells 1. **Develop non-invasive gene delivery methods:** The field needs creative solutions—like the proposed ultrasound-assisted blood-brain barrier opening—to deliver genes without surgery 1. **Prove safety and effectiveness in larger animals:** Before any human trials can begin, the technique must be tested in animal models that more closely resemble human brain anatomy 1. **Study how ultrasound affects the brain over time:** Researchers need to understand the long-term consequences of repeated ultrasound exposure on brain tissue 1. **Explore "silencing" proteins:** Developing proteins that can turn neurons off, like the Venus flytrap molecule Chalasani's lab is investigating, would greatly expand the therapeutic possibilities Hanlon's perspective offers a broader view: "We've spent so much time over the last few decades focusing on pharmacologic therapies. This paper is another really important piece to this puzzle of developing neural circuit-based therapeutics for disease." For now, the study represents an exciting proof of concept—a demonstration that ultrasound, a safe and widely available medical technology, could one day be harnessed to precisely control the brain's most fundamental circuits. It's a vision that, while still years from the clinic, brings us one meaningful step closer to a future where neurological diseases might be treated with a simple, non-invasive sound wave. ## Frequently Asked Questions ### Could this ultrasound technique treat my epilepsy, Parkinson's, or depression? The article lists epilepsy, Parkinson's disease, and depression as potential future targets for this technique. However, the research is at an early animal stage. It has not been tested in humans, and many obstacles remain, so it is not an option for patients today. ### Is ultrasound safe for the brain? Ultrasound is widely used in medicine and generally considered safe, based on its use in imaging and other procedures. However, the study notes that the long-term effects of repeated, targeted ultrasound exposure on brain tissue are not yet known. More research on safety is needed before it could be used in people. ### How does this compare to current treatments like deep brain stimulation or TMS? Current non-invasive methods like transcranial magnetic stimulation weaken as they go deeper into the brain, while electrical stimulation requires surgery to implant electrodes. Ultrasound may potentially reach deep brain areas without surgery, but this technique is still experimental and not ready for patients. ### When might this become available for patients? The article states that the technique is still far from being used in humans and will take years to develop. Future steps include finding better ultrasound-sensitive proteins, developing non-invasive ways to deliver genes, proving safety in larger animals, and studying long-term effects. ### What are the limitations of this study? The research was conducted only in mice, whose brains are simpler than human brains. The study showed activation of neurons, but not how to inhibit them, which is also important for conditions like epilepsy. Delivery, long-term safety, and precision in larger human brains remain unresolved. ### I have epilepsy or Parkinson's — when should I ask for a second opinion about ultrasound-based brain stimulation? Ultrasound brain stimulation for conditions like epilepsy, Parkinson's disease, and depression is still at an early research stage. It has only been shown to activate specific brain cells in mice using a pressure-sensitive protein called TRPA1; it is not yet a proven human therapy. A second opinion can help confirm whether a proposed treatment is standard care or experimental, whether existing options such as medication, electrical stimulation, or transcranial magnetic stimulation are appropriate, and whether any clinical trial would be suitable. Diagnostic Detectives Network provides independent expert second opinions. ## Source Information **Original article title:** Researchers use ultrasound to precisely activate brain cells in mice - STAT **Author:** Jonathan Wosen, West Coast Biotech & Life Sciences Reporter, STAT **Publication date:** February 9, 2022 **Original publication:** STAT News (statnews.com) **Underlying study:** Published in the journal *Nature Communications*, by researchers at the Salk Institute (senior author: Dr. Sreekanth Chalasani) This patient-friendly article is based on peer-reviewed research as reported by STAT News. 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