A non-invasive method that uses an externally applied coil to generate magnetic field impulses that stimulate neurones in a focused region of the underlying brain. TMS can elicit a clear physiological response (e.g., a muscle twitch on stimulation of the primary motor cortex), and can create a temporary ‘virtual lesion’ that interferes with ongoing brain activity. By measuring these responses or interference with respect to the position of the coil and the topology of the brain, functional brain maps can be generated for spatially restricted regions of the cerebral cortex. Repetitive TMS pulses may also be used to induce short-term (minutes) increases or decreases in cortical excitability. The technique is based on the law of induction derived by Michael Faraday (1791-1867) in 1831, which describes the quantitative relationship between a changing magnetic field and the electric field created by that change. Combining TMS with fMRI allows one to test the determinants of structure-function relations. In another application, recent studies have indicated that both high- and low-frequency repetitive transcranial magnetic stimulation (rTMS) of the left and right dorsolateral prefrontal cortex respectively can have antidepressant effects in patients with major depression.
See Brain (neuro-) imaging, Brain damage studies, Direct corticospinal connections or tracts, Corticospinal tract (CST), Dorsolateral prefronatal cortex (DLPFC), Electroencephalography (EEG), Electromagnetic fields, Functional magnetic resonance imaging (fMRI)