Selective attention regulates spatial and intensity information processing in the human primary somatosensory cortex

Attention-related cognitive processes in the primary somatosensory cortex (SI) were studied by measuring somatosensory evoked magnetic fields (SEFs). Twenty-one normal adult human subjects participated in this study for investigating effects of attention and stimulus intensity on cortical finger representation in the SI cortex. Electric stimuli at low and high intensity were delivered to the index or middle finger in finger discrimination and non-discrimination task. For the low intensity stimulation at 1.25 times sensory threshold, an early component (M50) showed clear segregation of the sources for the two fingers and an increase of the amplitude specific to the finger discrimination task. Such an attentional effect on the SI cortex was masked by the high intensity stimulation (2.5 times sensory threshold); the M50 source separation by the fingers was induced irrespective of the discrimination or non-discrimination task. The results suggest that a conscious regulation of stimulus intensity coding in the SI cortex underlies the attention-dependent enhancement of spatial finger information processing.