Volume conduction of the parietal N20 potential to the prerolandic frontal area

Somatosensory evoked potentials were recorded from the frontal and parietal areas in patients with various lesions in the central nervous system on stimulation of the median nerve. Five representative cases who showed a selective loss of the positive potential from the frontal area are reported. In each case, the parietal N20 potential was relatively well preserved, and the midposition between the frontal and central areas (FC area) showed a negative potential following P14. The peak of this negative potential was synchronous with that of the parietal N20 potential. This negativity on the FC area is considered to be a volume conducted potential from the parietal N20 to the prerolandic frontal area. Such an anterior volume conduction of the parietal N20 would not be explained by the concept of a tangentially oriented dipole generated in the posterior bank of the central sulcus. Instead, for the generator of the parietal N20 potential, a radically oriented dipole generated mainly in the parietal area is postulated.