Recent studies by Harvard researchers at McLean Hospital in Belmont, Mass., have enlarged the body of knowledge about a promising, though still experimental, treatment for a variety of psychiatric disorders. The treatment is called “transcranial magnetic stimulation,” and essentially involves placing a powerful electromagnet on a person’s scalp. The electromagnet alters brain activity by inducing an electromagnetic current in the underlying cortical neurons. Researchers aren’t sure why that would have a therapeutic effect. Pilot studies by a number of researchers at McLean and elsewhere have indicated that patients treated with TMS reported improvement in major depression, mania, post-traumatic stress disorder, Parkinson’s disease and obsessive compulsive disorder. The authors of a recent report that reviewed the research — Michael Henry, Alvaro Pascual-Leone and Jonathan Cole — concluded that TMS “appears to be a promising potential tool” but said that more studies need to be performed to provide convincing evidence of the tehcnique’s efficacy and safety. Henry is an instructor in psychiatry, Pascual-Leone is an associate professor of neurology and Cole is a professor of psychiatry.