Neuroscientists Created A New Brain Stimulation Technique That May Speed Up Learning

Transcranial temporal interference brain stimulation successfully improved motor learning, especially in older adults.

Complex neural network in the brain, depicting the connections between neurons
fotograzia/Moment/Getty Images

Zapping your brain smart sounds either like a “don’t try at home” science experiment or something that Generation Alpha will regularly do before their trigonometry final. But for years, scientists have sought to boost our brain’s functioning with electricity, similar to jumping a car (albeit more safely and less pinchy).

This idea led to non-invasive brain stimulation techniques like transcranial alternating current stimulation (using electrodes strapped to the scalp) and transcranial magnetic stimulation (using magnetic fields to stimulate neurons). And now, researchers in Switzerland have tested a new non-invasive method in humans called transcranial temporal interference brain stimulation (or tTIS).

In a study published Thursday in the journal Nature Neuroscience, the researchers used this method, which manages to penetrate deep brain structures without affecting brain tissues on top, to enhance motor learning in older, healthy adults.

“[This study] speaks to the emergence of a new and potentially powerful tool in our arsenal of ways to manipulate brain function,” Roy Hamilton, director of the University of Pennsylvania’s Brain Science, Translation, Innovation, and Modulation Center, who was not involved in the study, tells Inverse. “It has implications for our ability to understand how brain function is localized in the brain and maybe our ability to act on it ourselves, even if we don’t have neurological dysfunction. I’m cautiously — maybe a little less cautiously — optimistic.”

Tapping Buttons Like a Virtuoso

The problem with both transcranial current and magnetic stimulation is that while you can reach structures deep in the brain, you do so at the risk of stimulating brain tissue at the surface of the brain, Friedhelm Hummel, a neuroscientist at the École Polytechnique Fédérale who lead the new study, tells Inverse. Stimulating other brain regions than the one you want complicates our understanding of which quivering mass of neurons is responsible for the effect, whether that’s improved memory or motor learning.

A more crucial reason for delivering focused electrical stimulation deep inside the brain is because that’s where neural structures like the hippocampus and basal ganglia, which are both implicated in a variety of neurological and psychiatric disorders, are located. For example, in Parkinson’s disease, the electrical wiring of the basal ganglia (that drives various cognitive and motor functions) sparks out of control, leading to tremors and rigid movements. Similarly, the hippocampus — a brain area controlling both short- and long-term memory — is damaged and shrinks in Alzheimer’s disease, resulting in dementia.

Back in 2017, researchers at the Massachusetts Institute of Technology (MIT) devised a new way of boosting neural electrical activity without stimulating surface-level brain tissue. Called transcranial temporal interference, the technique involved placing electrodes on the head and emitting very high frequencies. Hummel says neurons on the surface of the brain don’t respond to these frequencies, but neurons deep in the brain, do. There, the high frequencies collide and cancel each other out, resulting in a lower frequency. Deep brain neurons seem to be more attuned to these lower frequencies, though neuroscientists are still not fully clear on all the mechanisms involved.

In that same study, the MIT researchers found that their temporal interference technique in mice stimulated the targeted hippocampus and not surface-level regions of the brain such as the cortex. These results looked promising to Hummel and his colleagues, and they wondered if they could carry over the same technique to humans to encourage brain flexibility, also known as plasticity, using a specific pattern of electrical pulses called “theta bursts.” Previous studies have found this particular frequency — evoking the theta waves our brains naturally produce — can help beef up plasticity.

The first part of the experiment had a group of 13 volunteers completing a learning task while receiving transcranial temporal interference electrical stimulation (or tTIS). As they completed the task, which involved pushing buttons in accordance with numbers on a screen (“It’s like a simple form of piano playing,” says Hummel), a functional MRI scanned their brain for any increases in neural activity — and there definitely were. Imaging revealed changes in blood flow in the striatum, a deep brain structure necessary for voluntary motor control as well as its associated motor network.

Participants had to complete a learning task, receiving either tTIS or a placebo electrical stimulation.

Friedhelm Hummel / EPFL

In a second round of experiments, the researchers had two groups of 30 healthy adults, one that got tTIS and the other a placebo with electrodes emitting a high frequency. Half of the volunteers consisted of people in their twenties; the others were in their sixties. None of the participants knew which treatment they were getting.

While they completed the same learning task, the participants didn’t have their brains scanned. The researchers were more interested in seeing whether the boost in electrical juice conferred any sort of cognitive advantage between the experimental and placebo groups. Hummel says it didn’t do much for healthy, young adults — tTIS only exerted a small effect compared to the placebo group — but it was a major difference for healthy, older adults who demonstrated enhanced motor learning while doing the piano-esque task.

“As soon as you moved into populations not functioning so well anymore, then the effect size is much, much bigger,” says Hummel. “Even when we trained them for only 20 or 25 minutes, the improvement was already more than 30 percent in the healthy, older adults.”

Adding to the arsenal

While the results seem promising, at least for aging populations where motor skills naturally decline with time, it’s worth remembering that this study is only a proof-of-concept and requires further exploration before possibly offering any clinical value.

“It seems like an important next step is trying to understand the mechanisms of tTIS better so that we can elicit larger effects,” Matthew Leonard, an associate professor of neurological surgery at the University of California, San Francisco, who was not involved in the study, writes to Inverse. “The results in this paper are impressive as an initial demonstration of feasibility, but it’s not clear whether the relatively small effects they observed would be clinically meaningful, for example, for patients with movement disorders.”

Even though the study didn’t include individuals with movement disorders or other neurological conditions, Hamilton of the University of Pennsylvania is optimistic these findings may prove clinically meaningful simply because there was an effect in older adults.

“Young individuals may be closer to the ceiling of effect. In other words, their systems processing this kind of information may be operating closer to their potential all the time,” he says. “Part of the rationale of why this approach in this study seems to have been beneficial for healthy older adults… they’re further away from the ceiling. If you apply that logic, it could be the case with people with disorders, they too are far from the ceiling of what could be achieved with respect to their brain function.”

The study also adds a new dimension to the debate of invasive versus non-invasive techniques in the field of deep brain stimulation. Leonard says that at present, there’s an “interesting tension in the field right now between more widely available invasive approaches, which seem to work quite well, and emerging non-invasive approaches that show great promise.” Since we still don’t know the limits of possibility with non-invasive methods, it remains to be seen whether they will dominate the future of deep brain stimulation.

Hummel acknowledges interventions like tTIS aren’t a one-size-fits-all approach. Depending on the patient and the purpose, whether treating chronic pain or neurological disorders like Parkinson’s disease, one method of deep brain stimulation over another may be more appropriate.

So, while you can’t zap your brain to be smart just yet, that future is anything but certain.

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