Three-dimensional localization of dipoles for potentials evoked by posterior tibial nerve stimulation in the monkey

Somatosensory evoked potentials (SEPs) elicited by right posterior tibial nerve stimulation were simultaneously recorded from 21-27 epidural electrodes in three monkeys. N23-P40 was recorded anterior to the left central sulcus, and P23-N40 was recorded on the parietal midline and the middle portion of the right hemisphere. These potentials were thought to be the primary cortical responses elicited by posterior tibial nerve stimulation in the monkey, since a topographical map made of them corresponded to the paradoxical lateralization of the primary cortical components in human posterior tibial nerve SEPs. Current source generators (dipoles) of these potentials were 3-dimensionally identified dipoles located in the left side of the mesial wall of the anterior parietal cortex, and oriented obliquely toward the right hemisphere by a dipole tracing (DT) method in which the 3-dimensional localization of dipoles in the brain were estimated and superimposed on magnetic resonance imaging (MRI) images.