| Abstract: | The scalp topography of the short latency somatosensory evoked potentials (SEPs) to unilateral posterior tibial nerve stimulation at the ankle was studied by using a non-cephalic reference in 22 normal young adults. At least 3 components (P28, N31 and N32) were identified preceding the major positive peak (P36). The first 2 components had similar peak latency at all scalp electrodes, and were considered to be generated in deep structures. However, N32 was localized to the hemisphere contralateral to the side of stimulation. P36 was maximal at the midline foot sensory area, or at the contralateral parasagittal area, and its amplitude decreased more steeply anteriorly than posteriorly. The peak latency of P36 progressively increased from ipsilateral to the side of stimulation in the coronal plane. P36 occurred earlier in the somatosensory area, and increased in peak latency anteriorly. Generator source of scalp-recorded far-field potentials (P28 and N31) remains to be elucidated. N32 might reflect activities of the thalamo-cortical pathway or an initial cortical response. P36 appeared to be generated in the somatosensory foot area. |
