てんかんに対する皮質電気刺激のメカニズムと臨床応用

Clinical application and mechanisms of electric cortical stimulation in human epilepsy

皮質電気刺激を用いた皮質機能マッピングは，てんかん外科治療の術前評価において既に確立した検査法であり，また様々な刺激条件を用いた皮質の刺激により，てんかん発作の軽減をはかる試みが始まっている。皮質脳波の周波数解析では，速波成分のパワーは高頻度双極刺激後，刺激部位にほぼ限局して減少する。これを用いて皮質活動性の変化を定量化し，さらに脳の興奮性・抑制性を適切にコントロールする刺激条件が明らかになれば，幅広い臨床応用が期待される。

Electric cortical stimulation is currently applied in the field of clinical epilepsy for cortical functional mapping during presurgical evaluation and for possible seizure control. Cortical electric stimulation to map cortical functions has been an established, gold-standard method since the Penfield's era, and recent studies showed that single pulse cortical stimulation could elicit cortico-cortical evoked potentials. It may help to understand the preexisting inter-cortical connectivity. Recent studies in animals and humans have demonstrated that both high- and low frequency electric cortical stimulation at seizure foci can suppress interictal spikes and seizures. Power spectrum analyses further demonstrated that high frequency stimulation can suppress background fast activities at the stimulated area in humans, that may suggest the inhibitory effects on the pyramidal neurons produced by cortical stimulation. Further information with regard to stimulating parameters to modify cortical excitability would promote clinical applications of electric cortical stimulation to control epileptic seizures in human epilepsy.