A brain stimulation technique that is used to treat severe depression could be improved with a new headpiece designed by University of Michigan engineers.
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.
In transcranial magnetic stimulation, coils create a fluctuating magnetic field that then generates a weak electrical field that can travel through the scalp and skull non-invasively. The electrical signal activates neurons in targeted parts of the brain.
Exactly how the technique alleviates depression isn’t well understood, but it tends to reduce symptoms in roughly half of patients who don’t respond to antidepressants. It’s been an FDA-approved mental illness treatment since 2006, but researchers say the technology is still relatively crude.
According to the university, it can only send signals 2cm into the brain before it causes uncomfortable muscle contractions in a patient’s scalp. It’s not the depth that causes the contractions but the relatively large focal spot required to go in that far.
‘I started working on transcranial magnetic stimulation a while ago and realized the technology was very limited,’ said Luis Hernandez-Garcia, a research associate professor of biomedical engineering and co-author of a paper on the work published in the October edition of IEEE Transactions on Biomedical Engineering. ‘If you wanted to reach deep in the brain, you also had to stimulate a lot of other brain regions that you really didn’t want to stimulate.’
To treat depression more effectively, it’s been hypothesised that the signal should reach beyond 2cm. In simulations at 2.4cm, the new system excited 2.6 times less unwanted brain volume than today’s systems. It can reportedly go deeper as well.
In a statement, co-author Eric Michielssen, a professor of electrical engineering and computer science said: ‘That improvement isn’t marginal. This should open up a lot of opportunities to treat depression and other mental illness, as well as probe the brain.’
According to a statement, the headpiece design is a departure from current figure 8-shaped devices made of 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.
Furthermore, the prototype only requires one power source, as opposed to 64 compared to other so-called multichannel arrays require a power source for each coil.