Although deep brain stimulation is effective at treating conditions such as Parkinson's disease, obsessive compulsive disorder, epilepsy, and depression, there's a catch – it involves surgically placing electrodes inside the brain. Not only is the procedure complex and invasive, but there are also risks involved, plus only specially-trained surgeons can do it. Now, however, scientists have developed a method of delivering the same sort of stimulation via electrodes placed on the scalp.
There is already a method of non-invasive brain stimulation, known as transcranial magnetic stimulation. One problem with it, however, is that it doesn't just stimulate one target area of the brain.
The new procedure – developed by a team from MIT, Beth Israel Deaconess Medical Center and the IT'IS Foundation – utilizes a phenomenon known as temporal interference. It utilizes as few as two scalp-mounted electrodes that each deliver a high-frequency electrical current into the brain. Each of those currents on its own is too fast to excite any neurons, so it won't have any effect on the parts of the brain through which it passes on its way to the target area.
At the point in the brain where the currents intersect, however, a region of low-frequency current is generated. This excites the neurons in that area only, while leaving surrounding tissue unaffected. In order to change the size and location of the area being stimulated, doctors simply alter the number and location of the electrodes, and/or adjust the frequency of the currents.
So far the process has been successfully tested on mice, which were made to move their limbs, ears, or whiskers by stimulating different parts of their motor cortex.
"We showed that we can very precisely target a brain region to elicit not just neuronal activation but behavioral responses," says MIT's Li-Huei Tsai. "I think it's very exciting because Parkinson's disease and other movement disorders seem to originate from a very particular region of the brain, and if you can target that, you have the potential to reverse it."