Somatotopic organization of human secondary somatosensory cortex

This fMRI study investigated the human somatosensory system, especially the secondary somatosensory cortex (SII), with respect to its potential somato topic organization. Eight subjects received electrical stimulation on their right second finger, fifth finger and hallux. Within SII, the typical find ing for both fingers was a representation site within the contralateral par ietal operculum roughly halfway between the lip of the lateral sulcus and i ts fundus, whereas the representation site of the hallux was found more med ially to this position at the fundus of the lateral sulcus, near the poster ior pole of the insula. Somatotopy in SII seems to he less fine-grained tha n in primary somatosensory cortex (SI), as, in contrast to SI, no separate representations of the two fingers in SII were observed. A similar somatoto pic representation pattern between fingers and the hallux was also observed within ipsilateral SII, indicating somatotopy of contra- as well as ipsila teral SII using unilateral stimulation. Further areas exhibiting activation were found in the superior and inferior parietal lobule, in the supplement ary and cingulate motor area, and in the insula.