Separate finger representations at the human second somatosensory cortex.

We recorded neuromagnetic responses of the second somatosensory cortex in healthy humans. Cutaneous electrical stimulation of fingers elicited a response around 100 ms, with a field pattern agreeing with activation of the second somatosensory cortex in the upper bank of the Sylvian fissure. In an oddball paradigm, with standards presented to the thumb and deviants (10%) to the middle finger, or vice versa, the second somatosensory cortex responses to deviants were almost three times as high in amplitude as those to standards. A similar amplitude enhancement was obtained when the deviants were presented in the absence of the intervening standards but with the same interstimulus interval. The results indicate that an accurate functional representation of different body areas is maintained at the human second somatosensory cortex.