Dipole tracing of monkey somatosensory evoked potentials

Current source generators (dipoles) of somatosensory evoked potentials (SEPs) in response to electrical stimulation of the median nerve in anesthetized monkeys were localized by the dipole tracing method (DT) which can approximate surface potential distributions to an equivalent dipole. The locations and latencies of dipoles estimated by DT were confirmed by recording multiple unit activities from the parietal cortices of the same monkeys investigated by DT. Loci of generators for each SEP component were: P10 and N10, area 3b; P12, areas 1 and 2; P18, area 5. The results indicate that DT could trace the successive movement of generators of SEPs from the primary somatosensory area to area 5, which has been suggested in neuroanatomical studies to be part of the hierarchical sequence of somatosensory processes.