The present results revealed two kinds of P300 activities in the dipole waveforms: a large, monophasic, P300 peak, which reflected the P300 data recorded at the parietal electrode sites, and a small, P300 peak followed by a negative slow wave, which reflected P300 data recorded at the frontal electrode sites. In the healthy control group, only the right frontal dipole resulted in a small, P300 peak, which may reflect an orienting response in stimuli-driven attention processes, and the result supported the target discrimination process underlying P300 response originates with right frontal activation. In the anxiety disorder group, a small, P300 peak followed by a negative wave was visible in the left-hemispheric frontal dipole and left-hemispheric temporal dipole, which reflects abnormal orienting response originating with left hemispheric activation. In depressive disorder patients, a small, P300 dipole peak followed by a negative, slow wave was obviously displayed in the right-hemispheric temporal dipoles, which suggests abnormal orienting response pronounced over the right-hemispheric temporal site.
