Transcranial magnetic stimulation

Transcranial magnetic stimulation is a technique that allows the induction of electrical current in the superficial brain tissue, by means of a rapidly changing magnetic field. It is a noninvasive technique which may be safely applied to awake and collaborating humans. The biological effects of transcranial magnetic stimulation can be classified as immediate, consisting of action potentials, and delayed, consisting of variably lasting changes in the excitability of neurons, outlasting stimulation itself. Accordingly, the impact of TMS on behavior can be generally categorized as “online” or “offline.” TMS produces behavioral changes by manipulating the firing characteristics of neurons. As a consequence, TMS may be used to establish causal relationships between brain and behavior. The direct effects of TMS have a limited spatial distribution, in the order of 1–2 cm, thus making it an optimal tool for hemispheric localization of brain functions. TMS has been applied to the study of lateralization of brain functions in humans in multiple domains such as language, spatial attention, or executive functions.