ANALYSIS OF BRAIN POTENTIALS RELATING TO COGNITION AND RESPONSE TO EXTERNAL STIMULI

正中神经刺激后的早期体感觉皮层反应包括不同频率范围的波，如自发脑电图。它们由顶叶n20 -额叶P20和中央P22电位组成，两者的电位范围为30-50 Hz。我们评估了身体感觉诱发电位的高频（>500Hz）成分是否可能是健康志愿者皮层反应的基础。我们发现600-800 Hz振荡叠加了N20-P20和P22电位。这些高频成分的峰值频率和幅度会随着被试的意识水平或注意力而变化。因此，可以确定高频振荡可能反映了认知过程。关于躯体感觉中枢传导时间，我们已经报道了初始皮层反应的开始时间与受试者的身高和年龄相关。我们还评估了如何确定皮层到达时间，并报告了头皮上的最佳电极位置和记录方法。在体感目标和非目标模式下，被试在识别体感目标刺激后，通过食指伸出作出反应，我们发现反应时间有时短于P300分量的峰值潜伏期。提示P300不仅反映认知，也反映决策后过程。

The early somatosensory cortical responses following median nerve stimulation include waves of various frequency range, as spontaneous EEG does. They consist of the parietal N20-frontal P20 and central P22 potentials both of which have 30-50 Hz range. We evaluated whether high frequency (>500Hz) components of somatosensory evoked potentials may underlie those cortical responses in healthy volunteers. We found that 600-800 Hz oscillations superimpose both the N20-P20 and P22 potentials. The peak frequency and amplitude of these high friquency components changed due to subjects' consciousness level or attention. It is therefore to be determined that high frequency oscillations may reflect cognition prosess. As to somatosensory central conduction time, we have reported that the onset time of the initial cortical response is correlated to subject's height and age. We also evaluated how to determine the cortical arrival time and have reported the optimal electrode positions at the scalp and recording methods.As to somatosensory target and non-target paradigm by which the subject is instructed to react by the index finger extension following recognition of the somatosensory target stimuli, we have found that a reaction time was sometimes shorter than the peak latency of the P300 component. It is suggested that P300 may reflect not only cognition but post-decision process.