Identification of activated area after intraoperative transcranial electrical stimulation for motor evoked potential

64例患者（经颅刺激（TCS）：29例，直接皮层刺激（DCS）：35例）被纳入本研究。从阈强度到200 mA，潜伏期逐渐趋于平稳，无“跳跃”现象。TCS与DCS的潜伏期差异很小。这些结果表明，当电流强度小于200 mA时，TCS的激活面积基本相同。200 mA TCS后对侧MEP波幅明显高于同侧，提示激活区不在脑干，而在皮质下，双侧皮质脊髓束走行较远。在两例MEP发生显著恶化的病例中，观察到术后对侧麻痹。这些病例中对应的病变是内囊，这意味着激活区域是内囊近端的皮质下。对于TCS-MEP监测，最佳强度被认为是小于200 mA的超大幅度所需的强度。

64 cases (Transcranial stimulation (TCS) : 29 cases, Direct cortical stimulation (DCS) : 35 cases) were included in this study. With increasing intensity from threshold level until 200 mA, the latency came to plateau, and no "jump" of latency was observed. The difference of latency between TCS and DCS was quite small. These results suggested that the activated area of TCS was almost same as far as the intensity is less than 200mA. The amplitude of MEPs after TCS with 200mA was much higher in the contralateral side compared to the ipsilateral, which suggested that the activated area was not brain stem but subcortex, where the bilateral cortico-spinal tract run distantly. In two cases in which significant deterioration of MEPs occur, postoperative contralateral palsies were observed. The corresponding lesions in these cases were internal capsula, which meant that the activated areas were subcortex which is proximal to the internal capsula. For TCS-MEP monitoring, the best intensity was thought to be the intensity needed for the supramaximal amplitude less than 200mA.