Navigated transcranial magnetic stimulation: Principles and protocol for mapping the motor cortex

Abstract

Transcranial magnetic stimulation (TMS) is a unique method for studying the human brain. Whereas the majority of imaging tools detect and map all the brain areas that participate during a given task (both primary and secondary network activations), TMS, when used to evoke a measurable physiological response, maps only those areas that are mandatory for the observed reaction. As such, TMS is particularly suitable for mapping cortical motor areas and for assessing the functional status of the motor tracts, both in normal subjects and in patients. In this chapter, we explore the physical and mechanistic background of using TMS to map the motor cortex. In addition, we outline a detailed protocol for mapping the cortical representation of various muscles—a protocol which can be used in basic research or as part of a clinical diagnostic or treatment procedure.