Transcranial Magnetic Stimulation: From Tool to Treatment

by Kayt Sukel

June 6, 2012

Nearly twenty years ago, when I worked as a neuroscience research assistant, I was asked to learn more about an up-and-coming technique called transcranial magnetic stimulation (TMS). At the time, several neuroscientists were using TMS to map cortical activity without cracking open the skull, by focusing its electromagnetic field on different brain regions and momentarily stopping cognitive processing in them.  Today , however, neuroscientists are using this unique tool in a new way. Physicians have moved TMS from the lab to the clinic, harnessing its ability to reshape brain circuits to treat psychiatric disorders including depression, attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), and addiction.

What is TMS?

It’s long been known that electrical stimulation can change neural processing. Electro-convulsive therapy (ECT) (often referred to as electroshock therapy), which applies a direct electric current to the skull, while doing wonders for severe depression but can also cause such adverse side-effects as seizure, memory loss, confusion, and long-term changes to cognition. Because TMS uses a magnetic coil to affect nerve impulses from outside the skull, though, it reduces the risks involved with direct currents.

“What TMS does is take electricity, create an isolating magnetic field in its coil, which then sends magnetic pulses across a patient’s scalp relatively unimpeded,” says Paul Croarkin, a doctor of osteopathy at the Mayo Clinic. “These magnetic pulses induce small electrical currents,and basically turn on the neurons underneath the coil. And those local superficial neurons in turn stimulate other neurons, leading to functional changes deeper in the brain.”

Anthony Barker, a researcher at a hospital in Sheffield, England, and his colleagues were the first to successfully use TMS to stimulate the motor cortex, inducing muscle contractions, back in 1985. Since then, neuroscientists have varied the location and configuration of the TMS coil to map cortical function by heightening or dampening neural activity in specific areas. As a consequence of that body of work, scientists like Alvaro Pascual-Leone, the program director of Harvard Catalyst Research Centers, wondered if perhaps doctors could use TMS to promote neuroplasticity in the brain—and “zap” the brains of those with psychiatric disorders back to more normal functioning by reducing or even removing incapacitating symptoms over time.

“It became clear over the course of these studies that when you apply TMS, you are not only going to modify activity of the brain for just the time you’re stimulating, but you are also going to induce changes that last longer than the stimulation itself,” he says. “That entered the possibility that maybe we could use TMS repetitively, to normalize activity in faulty brain circuits and specifically induce changes that are beneficial to a clinical population. “

TMS and rTMS in the clinic

People with debilitating depression are among the first to have benefitted from TMS. Repetitive TMS (rTMS), or the use of TMS for approximately 20-30 minutes every weekday for between four and eight weeks, has been approved by the Food and Drug Administration (FDA) for the treatment of major depressive disorder in adult patients who have not been helped by at least one antidepressant smedication.

“When you think about an illness like depression, studies have shown reduced functioning in some brain areas, increased functioning in others. The brain is out of balance in terms of its functional levels,” says Colleen Loo, a psychiatrist at the University of New South Wales who uses rTMS to treat people with depression. “And rTMS can stimulate the brain electrically and then correct those excitability levels over time.” 

Even with only modest success in using rTMS to treat depression, researchers like Loo and Abraham Zangen, a researcher at Ben Gurion University, are championing the use of rTMS to treat other disorders including OCD, ADHD, and even addiction.

“The brain is a complex organ that regulates so many things. Depression is one kind of syndrome. But there are so many others including psychosis, OCD, and addiction,” says Loo. “The ability to stimulate different parts of the brain using different stimulation parameters gives you great flexibility to investigate TMS’ therapeutic usefulness in quite a large number of different psychiatric disorders.”

Early studies have shown some promise in addiction. In the April 2009 issue of Addiction, Zangen and colleagues demonstrated that 10 daily rTMS sessions, focused on the left dorsolateral prefrontal cortex (DLPFC), reduced both cigarette consumption and craving in chronic smokers, even when presented with smoking-related pictures. More recently, Jed Rose, a researcher at Duke University, found that the repeated delivery of TMS to the superior frontal gyrus instead increased craving for cigarettes. This study was published in the Oct. 11, 2011 issue of Biological Psychiatry.

Both studies were preliminary—and Zangen acknowledges  that the effect in his study did not last for long. “We did not really get long-term abstinence in that study, which is what you want when treating addiction” he says. “But the results were promising.” His lab is testing different locations as well as timing and frequency patterns of TMS in cigarette smokers, and the early data suggest that some of them may promote kicking the habit for good.

Next steps

Zangen is enthusiastic about TMS’ possible therapeutic uses. “Based on the neuroplasticity concept, TMS—depending on the stimulation parameters, the coil configuration and location—can be used for therapy. It is not one tool, because each coil and each stimulation sequence is actually targeting a different circuit or chemical. It can be many tools, and something that may possible help treat many, many disorders.” 

Pascual-Leone agrees but cautions that we should also do more research to understand how exactly TMS is working its effects—down to the molecular level of the affected neurons. “There is a huge need for mechanistic studies that really clarify how TMS’ effects come about,” he says. “Before we understand how viable this tool is for all these different treatments, and how to best optimize it to help patients, we need better insight into what is happening at every level.”