A new headpiece for brain stimulation technique, designed by engineers at the University of Michigan, Ann Arbor, may considerably improve treatment of tough cases of depression. Computer simulations have shown that the device—a square array of 64 circular metallic coils—could help researchers and doctors hit more precise targets in the brain that are twice as deep as they can currently reach without causing pain.

Shown is the headpiece, a square array of 64 circular metallic coils, next to computer simulations of a brain stimulation. (Credit: Joseph Xu)

In transcranial magnetic stimulation, specialized coils create a fluctuating magnetic field that generates a weak electrical field that noninvasively travels through the scalp and skull to activate neurons in targeted parts of the brain. This treatment tends to reduce symptoms in about half of patients who don't respond to antidepressants.

The treatment method was approved by the FDA to treat mental illness in 2006. But, it can send signals only 2 centimeters into the brain before it causes uncomfortable muscle contractions in a patient's scalp due to the relatively large focal spot required to go in that far. To treat depression more effectively, it's been hypothesized that the signal should reach beyond 2 centimeters. In simulations, at 2.4 centimeters, the new system excited 2.6 times less unwanted brain volume than today’s systems. It can go deeper as well.

This type of neural stimulation is also a tool in the cognitive neuroscience field where researchers study how brain biology leads to thoughts and actions. For example, a neuroscientist can use it to activate regions of the brain thought to be responsible for hand movement and then watch for a hand response to confirm the hypothesis. To advance this field of study, scientists need the ability to zero in on smaller parts of the brain.

The headpiece design is a radical change from current devices made of just two coils. Working with metamaterials, which can focus light to a point smaller than its wavelength, they settled on a design with a surface of loops. The coil arrays are sub-wavelength structures devices designed to manipulate the magnetic near-field in ways not done before, they said.

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.