Cortical somatosensory potentials evoked by magnetic stimulation: effect of body height, age, and stimulus intensity.

Cortical somatosensory evoked potentials elicited by non-invasive magnetic stimulation at Th10, Th12, and L5 vertebral levels and at mid-gluteus and ankle were studied in 45 normal controls varying in body height and age. Peak latencies of P2 evoked by ankle, mid-gluteus and L5 stimulation were correlated with body height. However, P2 latencies evoked by Th10 and Th12 stimulation were independent of body height. In contrast, all N2 latencies evoked by Th10, Th12, L5, mid-gluteus and ankle were correlated with body height. There were no correlations between latencies of P3 and N3 and body height. No peak latencies of cortical components were affected by age within the age group studied (15-67 years). In the intensity study, N2 showed double peaks when low to moderate stimulus intensities were applied to Th12 vertebra. Furthermore, in 2 patients with mild somatosensory dysfunction of lumbar roots or cord, N2 evoked by L5 stimulation revealed double peaks with prolonged interpeak latencies between the first peak of N2 and P3, which might be related to the temporal dispersion of the afferent fibers. These data suggest that the N2 component is induced by both fast and slow afferent fibers.