Magnetic stimulation of the brain's left prefrontal cortex may help some depressed patients in much the same way as electroconvulsive therapy (ECT), but without its side effects, suggests a preliminary study by Mark George, M.D., of the National Institute of Mental Health (NIMH), Eric Wassermann, M.D., National Institute on Neurological Disorders and Stroke (NINDS), and NIH colleagues.

They found that two of six medication-resistant patients showed marked mood improvement after treatment with repetitive Transcranial Magnetic Stimulation (rTMS) over several days. One of the two responders, a middle-aged woman, reported feeling well for the first time in three years. Two other patients experienced slight mood improvement and two no improvement following the experimental procedure, which employs an electromagnetic coil that induces a current in the brain's cortex.

The treatment is administered daily for at least a week, much like ECT, except that subjects remain awake. Although proven effective for depression, ECT entails risks associated with a seizure, occasional memory loss, and general anesthesia, which is required. In the pilot rTMS study, two patients developed mild headaches, treatable with aspirin -- the only reported side effects. However, rTMS does entail some risk, especially for seizure-prone individuals, and would not neccessarily help all patients who respond to ECT.

Unlike electricity, which gets diffused by the skull, high intensity magnetic pulses pass readily through bone, making possible more focused targeting of particular brain structures. The NIMH investigators aimed the magnet at the brain's left prefrontal cortex, since it has been implicated as a site of abnormally low metabolism in studies of depression. PET (positron emission tomography) scans performed in one patient during and after treatment showed widespread increases in metabolism, hinting that the magnet's effects may be broadly telegraphed via interconnected brain circuitry, suggests Dr. George. A controlled trial of rTMS for depression is currently underway at NIMH -- the first of a series required before its safety and efficacy can be established.

Researchers hope this and other work with magnetic stimulation will shed light on the mechanism of action of ECT, which remains a mystery. If magnetic pulses can produce an antidepressant effect, then the seizure that occurs in ECT may not be necessary.

Evidence is emerging from animal studies about how electrical currents, such as those induced in rTMS, might alter brain mechanisms. For example, NIMH's Susan Weiss, Ph.D., finds that low frequency electrical stimulation triggers lasting anticonvulsant effects in rats. Other investigators have found that magnetic stimulation produces an antidepressant effect in some animal models of depression.

In addition to its possible therapeutic potential, rTMS is also being used as a selective probe in studies of human brain function. For example, depending on where the coil is placed, it can disrupt speech or interfere with different types of memory. Investigators are also following up clues that it may trigger different emotional states in normal subjects, depending upon magnet placement.

Findings of the pilot study were published in the Oct 2 issue of Neuroreport. In addition to George and Wassermann, co-authors of the article, "Daily repetitive transcranial magnetic stimulation (rTMS) improves mood in depression," are: Drs. Ann Callahan, Terrence Ketter, Robert Post (NIMH), Mark Hallett (NINDS), Wendol Williams (National Institute on Alcohol Abuse and Alcoholism), and Peter Basser (National Center for Research Resources).

NIMH and NINDS are components of the National Institutes of Health, an agency of the U.S. Public Health Service, part of the U.S. Department of Health and Human Services.

Information provided by the NIMH.
November 1995