Researchers develop a noninvasive method for deep brain stimulation

This approach could in future make deep brain stimulation safer, less expensive, and more accessible as a therapy for patients with brain diseases such as Parkinson’s or Epilepsy. The study, part funded by Wellcome and led by MIT researchers, collaborating with investigators at Beth Israel Deaconess Medical Center (BIDMC) and the IT’IS Foundation, is published today in Cell.

Deep brain stimulation - delivering an electrical current to deep regions of the brain involved in movement control - has proven successful in treating many Parkinson’s disease patients. Doctors also use deep brain stimulation to treat some patients with obsessive compulsive disorder and epilepsy.

However, this approach requires electrodes to be implanted near the base of the brain — a complex procedure that carries risks, including brain hemorrhage and infection.

“Current deep brain stimulation treatments can only be performed by a small number of neurosurgeons and involve implanting an electrode in the brain which can have complications. This study shows that it may be possible to noninvasively stimulate deep regions of the brain without harming any surrounding tissue. With the ability to stimulate brain structures noninvasively, we hope that we may help discover new targets for treating brain disorders,” says the paper’s lead author, Nir Grossman, a former Wellcome-MIT postdoc and current research fellow at Imperial College London.

In this new method, researchers devised a way to deliver electrical stimulation deep within the brain, via electrodes placed on the scalp, by taking advantage of a phenomenon known as temporal interference.

Two high-frequency electrical currents are generated using electrodes placed on the scalp. By themselves, the changing electrical currents happen too rapidly to stimulate neurons. However, at the location where the two currents intersect there is a small region of low-frequency electrical activity. The researchers show that this low-frequency current can stimulate neurons deep in the brain, while the high-frequency current passes through surrounding tissue with no effect.

By tuning the frequency of the two currents and changing the number and location of the electrodes, the researchers can control the size and location of the brain tissue that receives the low-frequency stimulation. This allows them to target locations deep within the brain without affecting any of the surrounding brain structures. They can also steer the location of stimulation, without moving the electrodes, by altering the currents. In this way, deep targets could be stimulated, both for therapeutic use and in basic science investigations to understand brain function.

MIT researchers tested this technique in mice and found that they could stimulate small regions deep within the brain, including the hippocampus. They were also able to shift the site of stimulation, allowing them to activate different parts of the motor cortex and prompt the mice to move their limbs, ears, or whiskers.

This study shows for the first time that it is possible to noninvasively stimulate deep regions in the brain, without harming any of the surrounding tissue. In the hippocampus experiments, the technique did not activate the neurons in the cortex, the region lying between the electrodes on the skull and the target deep inside the brain. The researchers also found no harmful effects in any part of the brain.

Previous pioneering work in animal models demonstrated how electrically stimulating the brain can have therapeutic benefits. This technology is now widely used in Parkinson’s disease, and is showing potential for other human brain disorders.

Dr Andrew Welchman, Head of Neuroscience and Mental Health at Wellcome, said: “This study is exciting as it provides a proof of principle that less invasive methods can be used for deep brain stimulation. The concept of delivering stimulation through intersecting electrical ‘beams’ is well established, but this study demonstrates how this technology could be put into practice. It’s an important step forward towards the goal of a non-invasive treatment for patients with serious neurological diseases.”