New perspectives in transcranial magnetic stimulation: epilepsy, consciousness and the perturbational approach

Transcranial magnetic stimulation (TMS) evolved from a simple method to stimulate the motor cortex to an invaluable tool for multiple diagnostic, research, and therapeutic applications. A further development of this noninvasive brain stimulation technique is concomitant electroencephalographic (EEG) recording during TMS. The theoretical underpinnings and the technological innovation of TMS-EEG co-registration have opened new ways to study brain excitability in neurological conditions previously investigated with conventional EEG alone. A further advance in TMS research applications is the perturbational approach: magnetic pulses can interfere not only with dynamic, often pathological rhythms in epilepsy or altered consciousness states, but also modulate physiological states such as sleep and sleep deprivation. So applied, TMS-EEG co-registration can reveal different neurophysiological and behavioral patterns in the awake state, sleep or sleep deprivation. In this review, we discuss the use of TMS and TMS-EEG co-registration in epilepsy, a still rather limited although promising area of study.