Attention induces reciprocal activity in the human somatosensory cortex enhancing relevant- and suppressing irrelevant inputs from fingers

Objective We studied whether attention regulates information processing in the human primary somatosensory cortex (SI) by selective enhancement of relevant- and suppression of irrelevant information. Methods Under successive and simultaneous electric stimuli to both the right index and middle fingers, tactile stimuli were randomly (20%) presented on one of the two fingers in separate two runs exchanging the finger. Subjects were requested to discriminate the tactile stimuli in an attention task to induce attention to one finger and to ignore the stimuli in a control task to avoid such an attention focus. Somatosensory evoked magnetic fields were measured only for the two-finger electric stimulation and an early component (M50) was analyzed. Results In spite of the two-finger simultaneous stimulation, attention to either the index or middle finger lowered or heightened the M50-sourse location, respectively. The attention task did not increase the M50 amplitude. Conclusions Attention to a finger enhanced selectively the representation of the finger in the SI cortex. However, this SI activity did not increase the M50 amplitude, suggesting that the attention suppressed another finger region receiving the unattended inputs. Significance Attention regulates the SI activity by selectively enhancing the task-relevant information and by filtering out other noise inputs.