This study presented the available effects of Source Derivation (SD) method for detecting the focal EEG, from the model experiments which were compared the traditional monopolar derivation with SD method, and also from the clinical recording for the patients, Signal dipole and EEG noise dipole embeded in a spherical volume conducted covered with three layer shells corresponding to neural tissue, skull and scalp, were used for the model. The following conclusions were obtained. 1) It was proved by the model experiment that SD method was useful for the detection of focal signal dipole potential on cortical surface. 2) SD method was useful to detect the signal not only in the cortical surface but also in the deep cortical area, when the reference electrode angle of SD method was smaller to the active electrode (α=10°-20°), that is, the distance of electrodes on scalp surface was about 1.6-3.2cm. 3) SD method was applied to the patients with focal spikes. The localization of the focal spike was more clear than the traditional ear reference monopolar recording. S/N to back ground EEG also was improved very well. 4) Identification of the location generated of primary responses in somatosensory evoked potential (SEP) by electrical stimulation of median nerve was tried by using the SD method with intererectrode distance of 2cm, and consequently the central sulcus and cortical primary sensory area were identified from the phase-reversal of SEP on the scalp.
