Activation of human mesial cortex during somatosensory target detection task.

We recorded somatosensory evoked fields (SEFs) from 10 healthy subjects to ulnar and median nerve stimuli presented at random intervals of 2.4-21.6 s. The subjects either counted the stimuli or ignored them by reading a book. The stimuli activated in both conditions the contralateral SI cortex, the ipsi- and contralateral SII cortices, and the posterior parietal cortex (PPC), in line with earlier observations. In addition, a novel response was observed in nine subjects at 120-160 ms. It was clearly enhanced by attention and was generated in the mesial cortex of the paracentral lobule, close to the end of the central sulcus.