MRI captures electric brain stimulation in action

Researchers have developed an MRI method to get a visual on electric currents affecting the human brain immediately after sessions of transcranial direct current stimulation (tDCS).

Although it’s not approved by the FDA for any treatment, tDCS is growing in clinical respectability as well as do-it-yourself popularity. Previous studies have suggested it can be a safe and effective way to improve cognitive performance and/or to counter the neuropsychiatric effects of depression, anxiety, Parkinson’s disease and chronic pain.

One of the questions skeptics have raised is whether the weak, 1- to 2-milliamp electric currents used in tDCS even penetrate deeply enough to stimulate or suppress neuronal activity.

With the new study, published Oct. 4 in Scientific Reports, senior author Danny Wang, PhD, of the University of Southern California and colleagues may have put that question to rest.

Wang and colleagues came up with an MRI technique that taps the linear relationship between direct current and induced magnetic fields.

The imaging ended up showing that, while tDCS may not directly cause neurons to fire, it does “create an environment that makes it more or less likely for neurons to fire,” as Wang puts it in a news article published by USC News.

In the journal report, lead author Mayank Jog, a graduate student at the David Geffen School of Medicine at UCLA and co-authors describe their work applying an MRI algorithm they created first to image the lower legs—this was to demonstrate in-vivo feasibility using simple biological tissue—and then the heads of 12 healthy volunteers.  

The human applications, which included 20- to 30-minute MRI scans post-tDCS, followed validation on a phantom with a known path of electric current and induced magnetic field.

The team found their algorithm verified when the phantom test closely matched the computational modeling.

Meanwhile the calf test was a moderate match, and the brain test showed expected magnetic field changes under and between the electrodes.

The researchers found that their proposed technique detected tDCS-induced magnetic fields as small as a nanotesla at millimeter spatial resolution.

However, acknowledging that computational modeling is not ideal for understanding what, exactly, tDCS is doing to the brain—too many variables are in play—the authors report that they did not perform the modeling on the brain scans.

Still, they believe their work points to a way forward in understanding tDCS.

“Through measurements of magnetic fields linearly proportional to the applied tDCS current, our approach opens a new avenue for direct in-vivo visualization of tDCS target engagement,” the authors conclude in their study report.

In the USC News article, Wang points out that the FDA has been unable to regulate tDCS as a clinical therapy because, until now, neuroscientists haven’t had a good grasp of how it may be that the electric currents affect the brain.

“Our study is the first step to experimentally map the tDCS currents in the brain and to provide solid data so researchers can develop science-based treatment,” Wang says.

Lead author Jog underscores previous studies showing that people only need two weeks of tDCS to show improvements and the effects can last beyond the treatment period.

“The technique fosters hope, but researchers need to get a better grasp on what is happening,” Jog says.

The journal has posted the study in full for free.