When medication and talk therapy don’t work, patients suffering with depression may turn to transcranial magnetic stimulation (TMS)—a noninvasive procedure that uses electromagnetic induction to produce weak electric currents inside the brain by using a rapidly changing magnetic field. But its present application is limited due to its outdated design. To make the treatment more effective, a research group at the University of Michigan, in Ann Arbor, designed a special headpiece to be placed on the skull that produces specially shaped electric currents in the brain.
Present TMS systems rely on figure-eight-shaped metal coils that also set up an electromagnetic field in the brain. But these coils produce a field that is both too wide and too shallow. Instead, the researchers designed a headpiece with electromagnetic properties tailored to produce a more focused and targeted field, according to IEEE Fellow Eric Michielssen, a professor of electrical engineering and computer science, who led the team. This is done with 64 interconnected copper coils laid out flat on the headpiece’s surface. Moreover, the coils have unequal diameters and spacings, calculated according to TMS coil-optimization software that the authors developed.
Tested through computer simulations, the results showed that the square headpiece, measuring 12 centimeters on a side, could reach smaller regions and about 0.4 cm deeper than the 2 cm it can reach today. It also reaches between 2.6 and 3 times less area than conventional figure-eight coils, respectively.
Their research, “Numerical Analysis and Design of Single-Source Multicoil TMS for Deep and Focused Brain Stimulation,” was published in October 2013 in the IEEE Transactions on Biomedical Engineering.
TMS treatments today are carried out in a therapist’s office. The patient sits in a chair similar to one in a dentist’s office, with the doctor placing the coils directly over the prefrontal cortex on the left side of the head, about 5 centimeters below the protruding part of the forehead.
IEEE Member Anthony Grbic, an associate professor of electrical engineering and computer science at Michigan and a coauthor of the report, says the uneven design of the coils produces better control of the direction of the electromagnetic waves.
The coil arrays are sub-wavelength structures designed to manipulate the magnetic field in a way that hasn’t been done before, Grbic says.
The new headpiece is compatible with present TMS systems and could eventually replace the coils used today. TMS is also used to study brain function. For example, researchers will stimulate a specific region to observe responses such as the movement of a hand or a change in behavior. With the ability to target smaller regions, neuroscientists will be able to learn even more about the brain, says team member Luis Hernandez-Garcia, an associate professor of biomedical engineering.
The team is working to shrink the size of the headpiece in hopes of targeting the treatment area even more precisely.
To validate its design and ensure that the treatment reaches the correct area, the team plans to combine its device with functional magnetic resonance imaging (fMRI), a neuroimaging procedure that measures brain activity, to observe the magnetic fields generated in the head.
“TMS depression therapy is not always effective because of the way we go about finding the region of the brain to treat,” says Hernandez-Garcia. “People’s brains are mapped differently. fMRI will help psychiatrists better control the region that gets stimulated.”
IEEE Student Member Luis Gomez, a doctoral student in electrical engineering and computer science who is also on the team, has developed a prototype of the headpiece and is looking to improve its functioning before testing it on animals in the lab. The team plans to test the efficacy of the device by using it to stimulate the brains of rats and thereafter start human trial.