Leo Sher, M.D.

Transcranial magnetic stimulation (TMS) is a neurostimulation and neuromodulation technique, based on the principle of electromagnetic induction of an electric field in the brain (1-3). TMS is a non-invasive method of stimulating the brain using induced currents. TMS device is a big capacitor that discharges thousands of amperes per pulse into the coil of an electromagnet, which generates the magnetic field. The coil is maneuvered to a spot on the patient’s head where the magnetic pulse will penetrate an area of the brain above and behind the eyes. The skull presents no barrier because the relatively low frequency magnetic fields pass through the skull without attenuation.The electrical current flow is accompanied by local neuronal depolarization about 3 cm in depth from the coil surface with an active area of depolarization on the cortex that is estimated to be 2 cm. Patients do not need anesthesia or sedation. Magnetic stimulation has the major advantage over electrical stimulation of being able to stimulate the human brain without causing pain. The term ‘fast’ or ‘high-frequency’ TMS is used to refer to stimulus rates of more than 1 Hz, and the term ‘slow’ or ‘low-frequency’ TMS is used to refer to stimulus rates of 1 Hz or less. This classification is based on the different physiological effects associated with low- and high-frequency stimulation. Studies have demonstrated that TMS to the left dorsolateral prefrontal cortex produces changes in prefrontal cortex, paralimbic, and limbic blood flow.

TMS is being studied for a variety of psychiatric disorders, including depression, obsessive-compulsive disorder, post-traumatic stress disorder, and auditory hallucinations in schizophrenia (1-7). The majority of the published studies show that TMS is an effective treatment for depression with response rates of 30–65%. Probably, treatment intensity, application of low- or high-frequency TMS and treatment duration may affect outcome. Specifically, 4–6 weeks may be needed for clinically meaningful outcomes. Some investigations suggest that patient age plays a role in TMS efficacy: younger patients are more responsive than older patients. In October 2008, the U.S. FDA cleared the NeuroStar TMS brain-stimulating device for the treatment of major depressive disorder in adult patients who have failed to achieve satisfactory improvement from one prior antidepressant medication at or above the minimal effective dose and duration in the current episode (8). A lot of studies need to be done on how the TMS works, why it works for some and not others, and how to make it work better.

References

1. Kim DR, Pesiridou A, O’Reardon JP. Transcranial magnetic stimulation in the treatment of psychiatric disorders. Curr Psychiatry Rep 2009;11(6):447-52.
2. Lisanby SH, Kinnunen LH, Crupain MJ. Applications of TMS to therapy in psychiatry. J Clin Neurophysiol 2002;19(4):344-60.
3. Rossi S, Hallett M, Rossini PM, Pascual-Leone A; Safety of TMS Consensus Group. Safety, ethical considerations, and application guidelines for the use of transcranial magnetic stimulation in clinical practice and research. Clin Neurophysiol 2009;120(12):2008-39.
4. Shelton RC, Osuntokun O, Heinloth AN, Corya SA. Therapeutic options for treatment-resistant depression. CNS Drugs 2010;24(2):131-61.
5. Avery DH, Holtzheimer PE 3rd, Fawaz W, Russo J, Neumaier J, Dunner DL, Haynor DR, Claypoole KH, Wajdik C, Roy-Byrne P. A controlled study of repetitive transcranial magnetic stimulation in medication-resistant major depression. Biol Psychiatry. 2006; 59(2):187-94.
6. Turnier-Shea Y, Bruno R, Pridmore S. Daily and spaced treatment with transcranial magnetic stimulation in major depression: a pilot study. Aust N Z J Psychiatry 2006; 40 (9): 759-63.
7. Su TP, Huang CC, Wei IH. Add-on rTMS for medication-resistant depression: a randomized, double-blind, sham-controlled trial in Chinese patients. J Clin Psychiatry 2005; 66 (7): 930-7.
8. DeNoon DJ. Brain-stimulating device cleared for depression treatment after 1 drug failure. http://www.webmd.com/depression/news/20081008/fda-oks-tms-depression-device Accessed April 16, 2010