Magnetism on the Brain

Abstract

FOR YEARS, SCIENTISTS AND PHYSIcians have been trying to tap into the brain to investigate and manipulate the neurons that make up its intricate circuitry. Such studies have sought, for example, to understand how thoughts are formed, to find ways to relieve intractable depression, and to block the neurodegeneration of such conditions as Alzheimer and Huntington diseases. One technique, transcranial magnetic stimulation (TMS), has been used by many scientists to turn on and off particular parts of the brain in research efforts. The technique has also been investigated as a possible therapeutic alternative to electroconvulsive therapy (ECT) for depression. But TMS, which was developed in the 1980s, has been slow to catch on as a viable therapy for psychiatric and neurological conditions because its effects have been small, variable, and short-term. Now, new research has demonstrated that TMS can be manipulated to produce more consistent and longerlasting changes in the brain. The findings have prompted some scientists to predict that the technique may eventually find a place in the clinic. It’s easy to understand why TMS has been considered a form of brain stimulation worth investigating for its therapeutic potential. Unlike such techniques as ECT or deep brain stimulation, it is not convulsive and does not require anesthesia or implanting devices within the brain. “This is very easy to apply, it’s noninvasive, and it doesn’t hurt,” said John Rothwell, PhD, of the Institute of Neurology at University College London, in London, England. The technique uses a magnetic coil housed inside a paddle that is held near the scalp. This coil produces a magnetic field that induces small electrical currents within the brain; dependingon the timingof treatment, it can either excite or suppress neurons directly beneath the paddle. But the technology’s limitations have tempered enthusiasm about its therapeutic potential. TMS fields do not penetrate deep into the brain, and researchers found that the excitatory or inhibitory effects on neurons rarely lasted longer than 30 minutes. Those limitations may not be insurmountable, however. Rothwell’s latest study has shown that TMS can be manipulated to produce rapid, consistent, and controllable changes in the brain that last twice as long as those produced by conventional TMS (Huang et al. Neuron. 2005;45:201-206). The findings, the researchers say, suggest that TMS may one day go beyond being a powerful research tool to become a potential therapy for a variety of brain conditions as well. TMS FOR DEPRESSION