TMS and electroencephalography: Methods and current advances

Electroencephalography (EEG) combined with transcranial magnetic stimulation (TMS) provides detailed real-time information about the state of the cortex. EEG requires only two to four electrodes and can be a part of most TMS studies. When used with magnetic resonance imaging (MRI) based targeting and conductor modelling, the TMS-EEG combination is a sophisticated brain-mapping tool. This article explains the mechanisms of TMS-evoked EEG. It describes the technique of recording TMS evoked EEG and the possible challenges for the same. Furthermore, it describes possible solutions to these challenges. By varying the TMS intensities, interstimulus intervals, induced current direction, and cortical targets, a rich spectrum of functional information can be obtained. Cortical excitability and connectivity can be studied directly by combining TMS with EEG or other brain-imaging methods, not only in motor, but also nonmotor, areas.