To create a control group, says Theodore, NIH scientists will angle the TMS coil so that some subjects don't receive brain stimulation.
Researchers also propose that TMS may help treat schizophrenia, a brain disorder for which few effective drugs exist.
In most cases, the severity and frequency of auditory hallucinations decreased more with the real TMS treatment than with sham applications.
Moreover, he charges that many investigators simply hold the TMS coil above a person's scalp, a crude technique that doesn't allow precise targeting.
They're now combining TMS and PET scans to determine how areas involved in speech production connect to each other and to the rest of the brain.
"One of the most powerful ways to map connectivity is TMS," says Fox.
The clinical condition that has brought TMS the most attention is depression.
There was another major reason to think that TMS might have a chance at treating depression.
The hope is that TMS can be a kinder, gentler version of ECT.
"In small, controlled studies of people who fail to respond to antidepressant medication, transcranial magnetic stimulation continues to show effectiveness," says Avery, who has created a database to consolidate TMS depression studies.
Investigators have begun to tease out why some people may not benefit from TMS. "We found that the longer the duration of the current episode of depression, the worse the response.
Several studies hint that TMS may rival ECT in effectiveness, at least for depressed people with no other psychological problems.