Repetitive TMS can cause an unintended seizure if researchers are not careful, according to George. It has happened about 15 times over the last 20 years of research. The risk of seizures relates to higher intensity (strength of voltage), higher frequency, duration of the stimulation and spacing between the stimulations.
Because of that risk, George said the International Society for Transcranial Stimulation in 2002 issued a consensus statement on managing the risks of rTMS when it is used in research studies (Belmaker et al., 2003).
According to the consensus document, individuals who administer rTMS should be trained as "first responders" in order to render appropriate care in the event of seizure, and rTMS should be performed in a medical setting under medical supervision with appropriate emergency facilities to manage seizures and their consequences. Additionally, patients and research participants should be continuously monitored during the administration of rTMS for signs of epileptic activity or other adverse effects by a trained individual, according to criteria established in the clinical or experimental protocol.
Belmaker et al. (2003) also stated that patients and study participants should be informed of the risk of seizure and its possible medical and social consequences and the dosage of rTMS should generally be limited by published safety guidelines.
Belmaker B, Fitzgerald P, George MS et al. (2003), Managing the risks of repetitive transcranial stimulation. CNS Spectr 8(7):489.
Chibbaro G, Daniele M, Alagona G et al. (2005), Repetitive transcranial magnetic stimulation in schizophrenic patients reporting auditory hallucinations. Neurosci Lett 383(1-2):54-57.
George MS (2003), Stimulating the brain. Sci Am 289(3):66-73.