Depression - Repetitive transcranial magnetic stimulation

Repetitive transcranial magnetic stimulation has been used as aphysical treatment approach for depression. It utilizes powerful magnetic fields which applied to the brain from outside the head. Multiple controlled studies support the use of this method in treatment-resistant depression; it has been approved for this indication in Europe, Canada, Australia, and the US. It was inferior to ECT in a side-by-side randomized trial.

In the procedure, special coils create a fluctuating magnetic field that generates a weak electrical field that can travel noninvasively through the scalp and skull. The electrical signal activates neurons in targeted parts of the brain. It can send signals only 2 centimeters into the brain before it causes uncomfortable muscle contractions in a patient's scalp. It's not the depth that causes the contractions. It's 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.

Researchers at University of Michigan have developed a new headpiece to address some of these issues. 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.

Computer simulations showed that the headpiece—a square array of 64 circular metallic coils—could one day help researchers and doctors hit finer targets in the brain that are twice as deep as they can reach today, and without causing pain.

The headpiece design improves on the current figure 8-shaped devices made of just two coils and uses a new metamaterial which has electromagnetic properties that can, for example, focus light to a point smaller than its wavelength.