New insights into brain function by combining transcranial magnetic stimulation and functional brain mapping

The present paper aims to summarize potential applications of transcranial magnetic stimulation (TMS) combined with functional brain imaging. Transcra nial magnetic stimulation is a well-established noninvasive tool for stimul ating circumscribed areas of the human cortex. Functional imaging technique s such as positron emission tomography,functional magnetic resonance imagin g,and electroencephalographic mapping enable assessment of TMS-related func tional brain activation. A combination of TMS and functional imaging can be useful in three principal ways. (1) Brain imaging before TMS is helpful in defining the accurate coil position over a distinct cortical area which is targeted by TMS. Since TMS can be used to interfere with regional cortical function during a given task, the effects of focal TMS on task performance can help to clarify the task-specific functional contribution of a given c ortical area which has previously shown task-related activation in a functi onal imaging study. (2) Imaging the brain during TMS is a promising approac h for assessing cortical excitability and intracerebral functional connecti vity. (3) By evaluating lasting effects of TMS, brain imaging after TMS can be employed to study the plasticity of the human cortex. Moreover, this ap proach will help to advance our understanding of therapeutical effects rela ted to TMS.