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Researchers have come a step closer to treating diseases like Parkinson’s and epilepsy, without the need to place an implant into the brain.

These days, many regions in the brain can be modulated by electricity to help improve brain function, in a technique already used to treat Parkinson’s and epilepsy. But because these cells tend to be deep in the brain, controlling them requires neurosurgical implants.



“If we could noninvasively stimulate deep regions, without hitting overlying regions, we might be able to help more people because we could stimulate deep regions selectively, without needing surgery,” Ed Boyden, professor at the Massachusetts Institute of Technology and co-author of the new paper, told WIRED.


Boyden and his team developed a technique to excite neurons deep inside the brain using only electrodes placed on a mouse’s head.

“We apply high frequency electric fields to different parts of the brain,” Boyden told WIRED. Brain cells cannot respond to high frequency fields, so the brain cells ignore these signals when sent on their own.

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“But where the high frequency fields overlap, we find they interfere with each other,” Boyden said. “That means that we can get a low frequency field, with the frequency numerically equal to the difference between the frequencies of the high frequency fields.”


For example, a 4,000 Hz electrical signal can be sent from one side of the head and a 4,001 Hz signal from the other side. When the two signals interfere in the brain, they will create an electrical wave at 1 Hz, the difference between the two signals. This low-frequency range to excite neurons.

This low frequency field amplitude can drive the neurons, thus making it possible to excite neurons deep in the brain without the need for a surgical implant. The technique is called temporally interfering (or TI) stimulation.

In the study, the researchers tested the model in 3D simulations and in live mice. Using mice, they found they could stimulate the brain to move things like a mouse’s right paw, whiskers, and ears, then its left paw, whiskers, and ears.

Although researchers know these low frequencies can stimulate brain cells, exactly why the technique works is less understood.

"We're reporting a biophysical discovery that neurons can respond to low-frequency envelopes of interfering high-frequency fields, but we haven't pinpointed the exact mechanism yet," says Boyden.


"One possibility is that neurons are nonlinearly reacting to the multiple fields, producing a signal at the difference frequency. Then, the low-pass filtering property of neurons is letting neurons respond at that low-difference frequency. But there could be other ways that the neurons are responding."

The authors hope to develop the results into a technique for use on humans, and they hope to do TI stimulation studies in human volunteers soon. “We are working on human studies now,” Boyden told WIRED.

The paper was published today in the journal Cell.