Applications of three-dimensional analysis to the auditory p300

Auditory Event Related Potentials (ERPs) to target stimuli were recorded by three orthogonal derivations from 18 normal subjects and were represented in three dimensional voltage-space (3-D), to produce Three Channel Lissajous' Trajectories (3CLTs). Target stimuli differed by pitch, phonemic or phonetic attributes. Assuming a central location, the orientation of the equivalent dipole moment was calculated for specific points (apices) along the trajectories. The apices roughly corresponded to the P300 peak in a voltage/time representation. The 3-D analysis resulted in a dipole pointing in a posterior-upward direction close to the mid-sagittal plane. Based on anatomical measures coupled with the behavioral role of the limbic system, we propose that a major contribution to the P300 to the stimuli tested derives from the outflows of the hippocampus and amygdala, i.e. fornix and stria terminalis. Orientation and laterality of the P300 dipole demonstrated clinical sensitivity beyond that of latency and amplitude measures in voltage/time representations.