Transcranial magnetic stimulation (TMS) is a relatively new neurological tool for treating conditions such depression and Parkinson’s disease, but because of technological challenges there’s a lot of work that’s being done to improve the delivery systems to be both safer and more precise. TMS requires using a coil to generate a rapidly changing magnetic field that induces electrical eddy currents within the brain, non-invasively activating neurons that are associated with whatever condition is being researched or treated. One major problem is that current TMS system designs can only generate sufficient eddy currents in the brain in wide areas and to a depth of about 2 cm before unpleasant side effects start to be observed, so researchers at University of Michigan engineered a new device that provides more signal focus and penetrates deeper than before.

The team created an array of coils that are are activated in a precise pattern according to a timing algorithm, resulting in a signal that can penetrate 2.4 cm while reducing the activated region by up to three times. Much like going from kitchen knife to a sharper scalpel, the new technology will open new possibilities for clinical applications in neurology and for scientific discovery in neuroscience.

From University of Michigan:

The headpiece design is a big departure from today’s figure 8-shaped devices made of just two coils. The researchers knew that in order to send a sharper signal, they’d have to change the shape of the fluctuating magnetic field the coils produce. To design a device that could do that, they worked with Anthony Grbic, an associate professor of electrical engineering and computer science who specializes in metamaterials—a class of substances tailored to exhibit specific electromagnetic properties that can, for example, focus light to a point smaller than its wavelength. Grbic suggested that a surface of loops could do the job. “These coil arrays are sub-wavelength structures—textured devices designed to manipulate the magnetic near-field in ways that people have never imagined before,” said Grbic, the Ernest and Betty Kuh Distinguished Faculty Scholar. The prototype needs only one power source, as opposed to 64. Other so-called multichannel arrays require a power source for each coil. Having just one would make it easier to use on patients and more affordable.

Study abstract in IEEE Transactions on Biomedical Engineering: Numerical Analysis and Design of Single-Source Multicoil TMS for Deep and Focused Brain Stimulation

UMich press statement: How a metamaterial might improve a depression treatment…