How scientists are using sound waves to hack the brain

The technique could lead to new treatments for brain disorders — or even a way to boost learning in everyone.

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The human brain may be the most complex structure in the universe.

It contains hundreds of billions of neurons, each sending signals to one another, forming complex circuits and networks that dictate practically everything you think and do. That means problems with these networks have the potential to impact nearly every aspect of your health and life.

Now, researchers in South Korea have figured out a way to use sound to influence the formation of connections between neurons — and not only could it lead to new medical treatments, it might even make learning easier for everyone.

Building a better brain

Because brain signals are electrochemical, some problems arising in the brain can be treated by altering the brain’s chemistry with meds — SSRIs, for example, treat depression by making more of the chemical serotonin available.

Existing brain stimulation methods are either invasive but precise, or noninvasive but harder to control.

If meds can’t help, though, doctors might try altering brain function by electrically stimulating the organ. This can be done either invasively, with brain implants, or noninvasively, with electrodes pressed against the head or magnetic pulses that pass through the skull

Brain stimulation has delivered remarkable results for some people with traumatic brain injuries, eating disorders, movement disorders, treatment-resistant depression, and more, but both approaches for administering it have limitations.

While implants can give doctors precise control over where and how the brain is stimulated, surgery is risky and can damage a patient’s brain. Brain implants typically become less effective over time, too, as scar tissue forms around them. Noninvasive techniques, meanwhile, are less precise and aren’t effective at stimulating regions deep in the brain.

A new approach

Ultrasound stimulation is a promising alternative to existing approaches. Not only can sound waves penetrate deep into the brain, but they can also be controlled with surprising precision, giving doctors the ability to stimulate specific regions without subjecting patients to invasive surgeries.

In previous studies, ultrasound brain stimulation has shown promise in treating depression, chronic pain, and Alzheimer’s, but there’s still a lot about the approach that researchers don’t fully understand, including how it works and how long its effects can last.

The ultrasound stimulation mimics brain waves linked to learning and memory.

Scientists at the Institute for Basic Science (IBS) in South Korea are now clearing up some of this mystery with a new ultrasound brain stimulation technique they call “patterned low-intensity low-frequency ultrasound (LILFUS).”

They designed this form of ultrasound to mimic brain waves that are common during learning and memory processes. The hope was that they could then use it to modulate neuroplasticity, or the ability of the brain to form new, functional connections.

In their study, published in Science Advances, they stimulated the brains of mice either continuously or intermittently (pulses of stimulation followed by brief periods of rest).

Following the intermittent stimulation, the potential to form strong connections between neurons in the targeted part of the brain increased. The continuous stimulation, meanwhile, had the opposite effect, reducing the potential for strong connections to form.

As for why this happens, the researchers think the ultrasound changes how a kind of brain cell, called “astrocytes,” absorbs calcium and releases chemicals that allow neurons to communicate. 

“According to our current understanding, the differential effects of intermittent and continuous stimulation are primarily associated with calcium dynamics within the brain,” lead researcher Park Joo Min told Freethink.

“[Intermittent stimulation] tends to induce a more robust calcium response, potentially leading to increased excitatory signals and neural activity,” he continued. “On the other hand, [continuous stimulation] may trigger less calcium modulation, resulting in a more inhibitory effect on brain function.”

A black and white photo of a mouse behind a piece of plastic with two vertical slots in it.
Institute for Basic Science
A mouse performing the pellet retrieval test

To test how their ultrasound stimulation might affect learning, the researchers delivered either intermittent stimulation, continuous stimulation, or a sham stimulation to the brains of mice before training them to grab food pellets through a slot in a transparent piece of plastic.

Applying the intermittent stimulation to the part of the brain controlling the mouse’s nondominant forelimb improved the mouse’s ability to use its “off-hand” for the task. The continuous and sham stimulation had no significant effect on learning.

This wasn’t the first study to indicate that ultrasound stimulation could modulate neuroplasticity, but the effect in past studies was short-lived, lasting only about 10 minutes, which limits its usefulness in the clinic. In this study, though, the effect seemed to last for about an hour.

“This approach not only provides precise stimulation of deep brain areas compared to existing non-invasive neuromodulation methods, like rTMS and tDCS, but also ensures long-term effects with minimal side effects,” said Park.

Looking ahead 

Much more research is needed to test the efficacy and safety of the IBS team’s technique, but if it can modulate neuroplasticity in people the way it can in mice, there are seemingly countless applications.

The intermittent stimulation could be useful in situations where increasing neuroplasticity might help patients, such as during stroke rehab or when trying to improve cognition in people with Alzheimer’s disease

Continuous stimulation, meanwhile, might be useful for preventing or reversing the formation of brain circuits that cause problems. This is called “maladaptive neuroplasticity,” and it’s been linked to certain psychiatric disorders, types of chronic pain, and more.

It’s possible the technique might even be able to improve learning for people who aren’t dealing with a health issue — imagine a future where a few minutes of noninvasive ultrasound stimulation prior to training could help you master a new skill more quickly.

“We are enthusiastic about the potential of this groundbreaking technology to revolutionize the treatment of brain diseases and enhance cognitive function, even in healthy individuals,” said Park.

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