Somatosensory Vertex Potentials: Comparison Between Bilaterally and Unilaterally Evoked Potentials

Somatosensory vertex potentials (SVPs), consisting of N1, P1, and N2, are obtained widely on the scalp between 100 and 500 msec of latency. To analyze interactions between SVPs evoked by right and left finger stimulation, the sum of N1-P1 or P1-N2 amplitude values in response to stimulation of independent right and left fingers were compared with those evoked by simultaneous stimulation of both fingers. SVPs were recorded at Cz, C3, and C4 in 12 healthy subjects. Three patterns of finger stimulation, namely, right, left, and both right and left, were randomly chosen until 80 responses had been obtained and averaged for each pattern of stimulation. Simultaneous bilateral responses were larger than either right or left finger SVPs. However, they were consistently smaller than summed SVPs from right and left fingers. These results suggest that the SVP generators be different between right and left. But they may be closely inter-related through occlusive connections.