Brain energy

NEW FRONTIERS

By altering or repairing brain circuitry, transcranial magnetic stimulation may help you enhance performance and resist depression and disease.

It's a scene straight out of a low-budget sci-fi movie:
In the Brain Stimulation Laboratory at the Medical University of South Carolina in Charleston, scientists position a powerful magnetic coil shaped like a figure eight on the scalp of a volunteer. When everything is ready, the lab's director, neurologist Mark S. George, M.D., throws a switch.

With a popping sound, the magnet begins generating high-energy magnetic pulses, each lasting only milliseconds. The volunteer feels a sensation like a pencil eraser being tapped repeatedly against the skull. Most of the magnetic energy, however, passes through flesh and bone and into the brain, where it is converted into electrical energy, triggering discrete areas of the brain. Depending on the magnet's position, it can make fingers twitch or cause volunteers to see bright flashes of light. Placed over the part of the brain that controls language, it can render subjects temporarily speechless.

Transcranial magnetic stimulation, or TMS, offers a noninvasive way to manipulate parts of the brain. For more than a decade, it's been used to map how brain functions are organized and to watch the way the brain changes as it learns new skills. But researchers hope it will ultimately do much more. Neurologists see TMS as a promising new way to treat brain disorders by repairing circuitry that has gone awry in conditions such as epilepsy, depression or Parkinson's disease. And a maverick band of investigators thinks that magnetic stimulation could enhance normal performance — potentially making it easier to learn a new language or solve the Sunday crossword puzzle.

a different magnetic beast
Magnets are hardly new to the field of alternative medicine. For years, claims have been made for the healing powers of magnetic mattresses and magnetic bandages, most of them unsubstantiated. Transcranial magnetic stimulation is a different beast. The magnetic fields generated by the coils are far more powerful than what a simple magnet can produce. And by tinkering with the pulse and direction of magnetic energy, researchers can vary the effect on specific brain cells.

Different frequencies of magnetic waves have different effects, explains George, one of the pioneers of TMS research. "Low-frequency magnetic pulses tend to relax an area of the brain, a kind of mental yoga. High-frequency magnetic waves tend to excite them, like a localized jolt of caffeine." The hope is that by activating dormant areas or quieting down overactive ones, doctors can fix abnormal brain function associated with a wide range of maladies.

One condition currently under investigation is depression. Psychiatrists have long known that electroconvulsive shock therapy, which delivers a serious dose of electricity to the brain — enough to cause a generalized seizure — can ease major depression in patients. Could the much smaller and more controlled amount delivered by TMS do the same thing? In one recent study, researchers at Australia's Monash University enlisted 60 patients suffering from depression and gave some of them repetitive TMS treatments daily while others received a placebo treatment that looked like TMS but didn't generate magnetic waves. Patients getting the real thing showed significant improvement in scores for depression after just four weeks of treatment. Also, researchers at the University of Illinois at Chicago reported that patients suffering from depression improved their scores after being given 10 to 20 TMS treatments.

Magnetic stimulation may also provide hope for those suffering from Parkinson's disease. At Egypt's Assiut University Hospital, researchers tested the therapy on 36 patients with the disorder, which interferes with normal motor movement. One group was given daily treatments that consisted of 2,000 pulses of TMS; the others received a look-alike treatment with no magnetic stimulation. In a paper published last year in the European Journal of Neurology, the investigators reported that the treatment group showed significant improvement in tests that measure motor movements.

Additionally, recent findings suggest that TMS may prove useful for quitting smoking. When researchers at Germany's University of Regensburg used TMS on smokers who wanted to kick the habit, volunteers smoked significantly fewer cigarettes during the six hours after their magnetic stimulation compared with subjects who were given a sham magnetic treatment.

boosting brainpower
If magnetic stimulation can repair abnormal brain function, could it also boost a healthy brain's thinking power? In 2001, scientists at the National Institute for Neurological Disorders and Stroke in Bethesda, Md., administered TMS to volunteers who were then asked to solve difficult geometric puzzles that required identifying similar shapes. "Subjects given TMS were able to solve the problems significantly faster," says Jordan Grafman, Ph.D., the senior investigator who led the study. "The improvement was small, but it showed up again and again."

Allan Snyder, Ph.D., director of the Centre for the Mind, part of the University of Sydney and Australian National University, has made the boldest suppositions, arguing that TMS can unlock mathematical wizardry or artistic powers that lie dormant. He has offered evidence in the form of drawings that become remarkably more sophisticated when the volunteers making them are given magnetic stimulation. However, many neuroscientists dismiss Snyder's claims. "We've been testing TMS on hundreds of research subjects for years," says Eric Wassermann, M.D., a neurologist at the National Institutes of Health's Neurology Institute, "and no one has suddenly revealed a sudden genius for anything."

Wassermann and some of his colleagues worry that some of the claims being made for TMS are outpacing the evidence. The study results on depression, for example, are inconsistent. While TMS is now approved for use to treat major depression in Canada, the U.S.

Food and Drug Administration has yet to give TMS its seal of approval. "The jury is still out on whether TMS will ultimately prove to be a useful therapy," says Wassermann. "We still have a lot to learn."

how deep does it go?
One unsolved puzzle is how TMS actually works in the brain. By delivering high-frequency magnetic energy, scientists suspect that the technique may increase the firing rate of brain cells slightly, making it easier for them to form the connections required for solving problems or learning new skills. On the other hand, low-frequency energy may wear brain cells out, temporarily reducing their activity or depleting their stores of neurotransmitters, the brain chemicals that transmit impulses. Or perhaps TMS succeeds simply by increasing blood flow to targeted areas of the brain.

"Frankly, no one really knows," says Grafman.

For years, it was assumed that TMS only affected the outer parts of the brain, called the cortex, because magnetic waves lose their power rapidly as they pass through brain tissue. Now, researchers are starting to suspect that they've underestimated the depth of TMS's reach. "Brain cells are massively interconnected," George notes. "It's likely that by stimulating cells in the cortex, we're also stimulating networks that reach deeper in the brain."

One unanswered question is how best to apply the technique. Investigators can vary everything from the level of magnetic energy and the duration of the pulses to where the magnetic coil is positioned and how often the treatment is delivered. But how these variations change the effect on the brain is only beginning to be explored. "The brain isn't a series of buttons to be turned on and off," says George. "The circuitry is extraordinarily complex, with networks in diverse parts of the brain firing at once."

Eventually, researchers may be able to develop integrated circuits that can stimulate several parts of the brain simultaneously. Along the way, George hopes that TMS will prove useful in treating chronic pain, schizophrenia, epilepsy and damage from strokes. And though magnetic stimulation probably can't create an instant Einstein or Mozart, it may otter clues into how to make us think faster or stay alert longer. "If we could change learning and memory by resculpting brain circuitry," says George, "the possibilities are endless."

"Generally, TMS appears to be free from harmful effects, ...
Examination of brain tissue submitted to thousands of TMS pulses has shown no detectable structural changes," states a report in Open Mind, the journal of the Tasmanian Association for Mental Health.

"Subjects given TMS were able to solve [geometric identity] problems significantly faster. The improvement was small but it showed up again and again."

In a trial conducted at the University of Tuebingen in Germany, investigators used TMS on 14 patients with persistent ringing in the ears, or tinnitus, which often results from noise-induced damage. After treatment, eight of the patients reported reduced symptoms.

By stimulating particular areas of the brain, researchers may be able to determine where memories or abilities will be stored. Theoretically, the technique could be used to generate back-up files in the brain for key memories or important skills.

In a study of smokers wanting to kick the habit, volunteers smoked significantly fewer cigarettes during the six hours after getting TMS than subjects given a sham magnetic treatment.

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By Peter Jaret

Illustration by Tom Collicott

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