Transcranial magnetic stimulation (TMS) is used to study cortical function by applying localized magnetic fields in a noninvasive manner. This chapter reviews the basic principles of TMS, including the stimulator unit, coils, and the interaction of TMS-induced electric field with the cortex. The advantages of TMS over invasive brain mapping techniques are highlighted. Improvements in the spatial accuracy of TMS are described in the context of image-guided TMS. Types of responses induced by motor cortex stimulation and their utility in mapping normal and diseased motor cortex are discussed. Language mapping with TMS takes advantage of the TMS-induced transient disruption of function, also termed “virtual lesion.” The authors provide examples of successful application of TMS in presurgical mapping of the motor and language areas in the brain. Emerging applications of TMS in the diagnosis of neuropsychiatric disorders and safety of TMS are also discussed.
Transcranial magnetic stimulation combined with electroencephalography in severely brain-injured patients: methodological aspects