When American psychiatrist Mark S. George stepped into the elevator of a London hospital in 1990, he had no idea the short ride would transform his research career. A fellow passenger was having a giggling fit for no apparent reason. When George inquired about the outburst of merriment, the man replied that a doctor had held a magnetic coil against his head and that it had made his thumb twitch uncontrollably.
Even though the tale sounded a bit like quackery, George was curious. He contacted the doctor, who said he had stimulated the man's motor cortex, located at the top of the head, in hopes of seeing whether it would spark a signal to any muscles. The doctor had learned about what researcher Anthony T. Barker of the University of Sheffield in England did in the mid-1980s: Barker transmitted 4,000 amperes of current through a copper coil to create a strong, tight magnetic field, then held his homemade device against his own head. His thumb suddenly jerked up involuntarily. The magnetic field had obviously been strong enough to deliver a stimulus to the brain through the skull--transcranially.
George asked the doctor if he had ever tried the device on the frontal regions of the cortex. The doctor replied no and wondered out loud why anyone would want to do that. When George returned to his laboratory at the Medical University of South Carolina, he proceeded to answer the question himself. He had a hunch that if the technique worked, it could perhaps help patients suffering from severe depression, for whom conventional treatment with antidepressant medication had failed. George focused a strong magnetic field on the left prefrontal cortex--the region of the brain that is underactive in clinically depressed people--and found that the mood of two of his patients improved, at least for a few days.
Since that time, interest in transcranial magnetic stimulation, or TMS, has blossomed. Physicians have since reported success in curbing epileptic convulsions and even in reducing the notorious shakes of Parkinson's disease. Some investigators today also hope to awaken hidden creativity and heighten consciousness in the average person. Others are skeptical, however, because controlled trials have been few, and even George warns against touting the young technique as a panacea.
It is still unclear exactly what this method does to the brain, he says, and anything that has the power to heal can also certainly harm. It is worth noting, too, that although the U.S. Food and Drug Administration has approved TMS devices for diagnostic applications, it has not approved them for any kind of therapeutic use.
Better than Shock Treatment
The basic principle of TMS is simple. A coil of wire is placed near the head. Alternating current flowing through the coil induces a magnetic field with a strength of up to 2.5 teslas (one tesla is 20,000 times the strength of the earth's magnetic field). The field passes harmlessly through the skull and influences the electrical signals passing among neurons in the brain.
Physicians hold the coil close to whichever brain region they are interested in stimulating. One variation, known as repetitive transcranial magnetic stimulation (rTMS), is to switch the current on and off from one to 100 times a minute, which creates a series of magnetic impulses. This approach is often used in experiments on people with depression. Remarkably, rTMS can elicit two opposing reactions: a low frequency will block neural activity, yet higher frequencies will stimulate it. It is the stimulation that appears to lift the veil of depression, perhaps by promoting the release of important neurotransmitters, such as serotonin, which can raise activity in neurons to normal levels.
The magnetic wand offers several advantages over other therapeutic methods. It is noninvasive and painless. Subjects have reported no discomfort other than what they describe as a slight pull on the scalp. Mild headaches are common side effects, but they seem to be relieved readily with typical over-the-counter medication. The apparatus, however, makes a loud noise, which can be annoying. And a handful of patients have had seizures. Yet this seems, overall, more palatable than the side effects of the primary technique used on severely depressed patients who do not respond to medication--electroconvulsive therapy, better known as shock treatment. In this approach, a patient is given general anesthesia as well as muscle relaxants. A strong electrical impulse is delivered through electrodes on the patient's head, triggering a convulsion in the brain. This uncontrolled thunderstorm of neuronal firing relieves depression for a short time for roughly 80 percent of cases, which is encouraging, yet subjects also often experience heart palpitations as well as subsequent confusion and memory lapses.
The positive effects of TMS are intriguing. In 1999 Ehud Klein, a psychologist at the Rambam Medical Center in Haifa, Israel, led the largest study to date. Klein exposed 70 patients suffering from major depression to 10 daily sessions of repetitive TMS over a two-week period. Half received real TMS, and half received a sham version--the magnet was held at an angle that rendered the field ineffective. The mood of participants who had been properly exposed improved on the Hamilton Depression Rating Scale, used to assess symptoms. But no change was found for subjects who had sat under the ineffective coils.
TMS is still in an extended experimental stage, however. Only a few trials, involving a small number of test subjects, have been published; there has been little follow-up. The types of people, brain locations, coil configurations, and magnetic field strengths and frequencies have varied considerably, making it practically impossible to compare study results. Positive effects, if they exist, may result from a combination of all the variables, George says, and I doubt that we've hit upon the most effective arrangement. A metastudy of depression trials also concluded there was no strong evidence of benefit.
Another deficit is that therapeutic effects seem to last only a few days to a few weeks. For example, Thomas Schlaepfer, a psychiatrist at the University of Bonn in Germany, was able to reduce obsessive behavior in one of his female patients. For years, the woman had found it necessary to perform a series of complicated rituals before she could pass through a doorway, but after a TMS session she was immediately able to walk from one room to the next with no hesitation. Unfortunately, she reverted to her old behavior after only a week.
Still, even this duration shows that the effect on neurons does not disappear as soon as the coil is removed. The procedure does more than simply intervene among neurons; it somehow transforms the neuronal network for a time. Molecular studies by neuropsychologist Armand Hausmann of Innsbruck Medical University in Austria suggest that TMS stimulates neuronal factors that are known to aid in cell growth.
Devil in the Details
If TMS can promote neuron growth, then it could potentially help people who suffer from degenerative brain diseases such as Alzheimer's, although that is speculation. Strengthening neural networks means that TMS could perhaps promote cognition and creativity, too. These possibilities require some leaps of faith, but a smaller step can be gleaned from TMS's history thus far. The technique has been most widely used as a diagnostic tool to stimulate specific regions of the cortex, helping neurologists gauge their function.
When Alvaro Pascual-Leone, a brain researcher at Beth Israel Deaconess Medical Center in Boston, managed to direct a coil at the language center of his participants, they suddenly could not utter a single word. TMS literally left them speechless. Peter Eichhammer of the University of Regensburg in Germany has provided at least some relief for people who suffer from tinnitus--a persistent, even maddening ringing or buzzing in the brain. After five half-hour treatment cycles, some participants reported a substantial decrease in background noise, which for a few individuals lasted up to six months.
Other work is further on the fringe. George has an agreement with the U.S. Department of Defense to try to use magnetic stimulation to keep fighter pilots alert and attentive. The dream is a TMS helmet that will animate exhausted soldiers back into battle. Michael A. Persinger of Laurentian University in Ontario has wired magnetic coils inside a motorcycle helmet that he says has enabled experimental subjects to believe they sense the presence of a supernatural being; some have reported encounters with a guardian angel; still others state they have encountered Satan. As a result, Persinger suspects that spiritual experiences are nothing more than a product of our brains.
Your Inner Savant
More tangible, but equally elusive, is the notion that TMS could heighten creativity. Allan Snyder, director of the Center for the Mind in Canberra and Sydney, Australia, foresees a thinking cap that will help psychologically healthy individuals attain unimagined heights of consciousness. He would like to awaken the slumbering genius in all of us with a kind of magnetic brain doping.
Snyder's inspiration comes from savants--autistic and other severely handicapped individuals who nonetheless display remarkable skills in certain cognitive areas. Some are gifted musicians, mathematical geniuses or outstanding artists. In most savants, the left hemisphere of the brain, considered to be the chief regulator for behavior, is chronically underactive. Snyder believes that the right side of the brain compensates with increased activity, bringing latent talents to the fore. He contends that temporarily switching off the left hemisphere with magnetic fields could allow pent-up creativity in the right hemisphere to spring forth. I've always wanted to know what would happen if we could suddenly see the world without any censorship, Snyder says. He reports that he has temporarily slowed the left hemisphere's activity in test subjects and that their thinking became less reason-driven, less stuck in its tracks.
The popular media has seized on Snyder's work and made it appear that such sharp targeting of our brain is already a reality. But scientists harbor a number of well-founded objections to findings of anything that could be called heightened creative skills. Yet speculation about fanciful applications abound. For example, students could block a brain region responsible for anxiety before an exam, improving their performance. In theory, no part of one's mind would be shielded from magnetic influence. If true, could TMS make people always speak the truth, vote for a specific political party or even murder someone? Although such potential misuse of TMS may only be a threat in the distant future, this technology calls for ethical discussions today.
