Howard Eisenberg, professor and chief of neurosurgery at the University of Maryland School of Medicine, participated in the clinical studies of FUS as an ablative treatment for essential tremor and Parkinson’s disease, targeting different brain areas for each disorder. He has found that patients like the technology because it’s less invasive than deep brain stimulation, which requires surgery to implant an electrode. “It’s not surgery really,” says Eisenberg. In addition, because FUS is so precise, says Eisenberg, “you can sculpt the lesion, you might make three ablations all close to each other.”
Comparatively speaking, neuromodulation, which entails altering electrical and chemical signaling in brain circuits, requires lower doses of energy that are delivered as intermittent pulses, and is relatively far down the list of possible uses for FUS in the brain. “It’s a frontier approach,” says Eisenberg, who is more excited about using FUS to open the blood brain barrier for drug delivery But if the technique can be perfected as a method of brain stimulation it will open a new range of possibilities. It can be aimed more precisely—on the order of millimeters rather than centimeters—than transcranial magnetic stimulation (TMS). And it can go deeper into the brain. “I think the first opportunity is on the diagnostic side,” said Kubanek. “Disease circuitry might be variable across patients. If we can specifically stimulate regions deep in the brain and measure the reduction of tremor, that would [tell us that region is] involved in that behavior.” The next step would be to apply focused ultrasound as a method of brain stimulation for a variety of mental health and neurodegenerative disorders like Alzheimer’s.
Like Kubanek, Seung-Schik Yoo, professor of radiology at Harvard Medical School and director of the neuromodulation lab at Brigham and Women’s Hospital, demonstrated successful brain stimulation using FUS at the Society for Neuroscience meeting. In sheep, Yoo and his colleagues showed that FUS could both excite and inhibit brain activity without apparent harm. But Yoo’s primary aim was to develop a wearable transcranial FUS system. His team created a small apparatus weighing only a quarter of a pound that could be worn by the sheep, whose cranial structure is similar to humans. The system consisted of a focused ultrasound transducer to generate the signal, an optical tracker and an applicator to hold the transducer over the head via an implanted pedestal. (In humans, they plan to do away with the need for implantation.) The group also developed a computer algorithm capable of predicting the intensity and location of the acoustic focus, which Yoo likened to an area the size of a large piece of orzo pasta.
“The tools themselves are really changing the face of what’s possible,” Mayberg says. “Wouldn’t it be great if we could tune [brain circuitry] with ultrasound and don’t have to open the brain?” she says. That would avoid surgery and the need for periodically changing batteries. “You could wear a device like the sheep,” she adds. “We can start to dream about some innovations that are based on exquisite neuroscience.”