[Transcranial magnetic stimulation in the study of epilepsy].

Several methods can be used to treat patients with epilepsy: antiepileptic drugs(AED), surgery and neuromodulation. AED is the most common method and also the first choice in the treatment of epilepsy. However, some patients are drug-resistant, or encounter severe adverse effects. In this case, surgery is an alternative to drug therapy for part of these patients. But surgery has several drawbacks: one is its invasive, the other is its high cost, and the third is its requirement for highly equipped medical devices to delineate the epileptiogenic zones. These factors limit its wide use in the clinical field. Epileptic conditions are characterized by an altered balance between excitatory and inhibitory influences at the cortical level(Tassinari et al.,2003). Antiepileptic drugs work by counteracting such imbalance with different mechanisms(Kwan et al.,2001). It is well known that the excitability of cortical networks can be modulated in humans by trains of regularly repeated magnetic stimuli(Wassermann&Lisanby,2001). Therefore, Repetitive transcranial magnetic stimulation (rTMS), a noninvasive and easily applied technology, could even have therapeutic effect in epileptic patients. Although some conflicting results have been reported, growing evidence shows that low-frequency (<1Hz) rTMS (slow rTMS) can significantly reduce seizure frequency and interictal epileptiform discharges. In this chapter, we aim at providing the reader with the most recent information on the application of TMS in epileptic conditions. This chapter is composed of 6 sections. First, the different ways and parameters that TMS can be used to investigate cortical pathophysiology are introduced. According to the patterns of stimulation, TMS can be divided into at least 3 categories: single-pulse TMS (sTMS), paired-pulse TMS (pTMS) and repetitive TMS (rTMS). Each TMS may reflect different brain cortical functions or have different physiologic effects. The parameters used as TMS study include motor evoked potential (MEP), motor threshold (MT), cortical silent period (CSP), intracortical inhibition (ICI) and intracortical facilitation (ICF). These parameters can reflect the functional state in motor cortex and motor pathway in different ways. The second section will discuss the possible antiepileptic mechanisms of rTMS in four aspects: electrophysiology, neurotransmitters, ion channel structure and function, as well as neuronal insults. The third section will refer to two issues: the effects of different AEDs on TMS parameters; the relationship between the changes of TMS parameters and corresponding AED serum