SAFETY OF RAPID-RATE TRANSCRANIAL MAGNETIC STIMULATION IN NORMAL VOLUNTEERS

In 9 normal volunteers, we studied the safety of rapid-rate transcrani al magnetic stimulation (rTMS) applied to different scalp positions at various frequencies and intensities. Pure tone threshold audiometry s howed temporary threshold shifts in 3 subjects. In the subject stimula ted at the highest intensity, rTMS induced a focal, secondarily genera lized seizure despite the absence of definite risk factors for seizure s. Rapid-rate TMS did not result in any important changes in the neuro logical examination findings, cognitive performance, electroencephalog ram, electrocardiogram, and hormone levels (prolactin, adrenocorticotr opic hormone, thyroid-stimulating hormone, luteinizing hormone, and fo llicle-stimulating hormone). In 10 additional subjects, the electromyo graphic activity in several contralateral muscles showed that trains o f rTMS applied to the motor cortex induced a spread of cortical excita bility. The spread of excitability depended on the intensity and frequ ency of the stimuli and probably constituted an early epileptogenic ef fect of rTMS. Guidelines for preventing the undesirable side effects o f rTMS are offered.