By means of Electric Brain Signal Imaging 128 channel system (Model ESI 128)

we studied the somatosensory evoked potentials (SEP) elicited by electrical acupuncture in left LI 4 and its near control point in high spatial temporal resolution. Result showed that

during 17～60 ms after the stimuli was given

① the whole cerebral cortex all responsed to the stimulation in LI 4; ② on the beginning negative potentials of N 1

the amplitude of SEP by LI 4 stimuli was lower than that by control point

While in the later potentials of N 2

the amplitude of SEP by LI 4 stimuli was markedly higher than that by control point. It proved that the exciting process in cerebral cortex after LI 4 might have some special properties

which might be related to the clinical effectiveness of acupuncture.