According to an article by Mark Hallet published through the National Institute of Neurological Disorders and Stroke, Transcranial Magnetic Stimulation (TMS) is becoming an increasingly popular non-invasive tool for studying the human brain. Magnetic stimulation is administered through the use of a coil placed above the scalp. A magnetic field is created through horizontal lines of flux on the coil. This field is then used to induce weak electric currents to the brain.
The stimulation can be used to evoke or inhibit various parts of the brain, by either inducing depolarization or hyperpolarization, respectively. Many researchers have used this tool to study parts of the brain. We can use this method to observe which parts of our brain are important for various tasks. For example, scientists can give patients simple eye tests under normal circumstances. Then, they can use TMS to inhibit areas of the brain, such as the occipital cortex. The researchers then repeat the eye tests, observing the effects. This method is powerful today as we try to ?tease apart specialized processing mechanisms.? Aside from the interruption of brain activity, this technique is also used in the growing research of brain plasticity. Single pulse TMS can be used along with functional neuroimaging (PET scans and fMRIs) in the continued research of human physiology.
Single pulse TMS is the safest and most common method, but repetitive TMS (rTMS) can be used to treat a number of disorders?including migraines, strokes, Parkinson's disease, dystonia, tinnitus, depression and auditory hallucinations. By exciting various parts of the brain, we can uncover complications in the brains of unhealthy individuals, and sometimes, researchers can quantify physiological effects of various damaged mechanisms. rTMS is used therapeutically because, unlike single pulse TMS, it has been shown to have lasting effects on the human brain, even after the magnetic stimulation ends. By varying the frequency of the stimulation, parts of the brain?s function can be enhanced or depressed (fast rTMS=enhancing, slow rTMS=depressing).
Therapeutic use was more recently brought to light by the observation of rTMS in some Parkinson?s patients. In some studies, the patients? responses were sped up by the stimulation. With disorders such as dystonia, rTMS actually works to inhibit parts of the primary motor cortex in an effort to improve performance in patients with this neurological movement disorder. Research is continuing to grow as we experiment with the idea of TMS treatment of people with mood disorders. Thus far, high-rate stimulation to the left dorsolateral prefrontal cortex and low-rate stimulation to the right dorsolateral prefrontal cortex have been shown to be helpful.
Unlike single pulse, rTMS has had some negative effects, such as seizure and syncope in healthy individuals. With few cases of negative side effects, the risk is considered to be fairly low. However, the benefits of TMS (in therapeutic scenarios) have not always been promising?the research is spotty: sometimes it works, and sometimes it does not. If scientists can solidify their findings, TMS could definitely be used in a regular clinical setting.
main article: http://www.psicomag.com/biblioteca/2000/hallet_00.pdf