Tactile stimulation of the hand causes bilateral cortical activation: a functional magnetic resonance study in humans.

The purpose of the present study was to assess the somatotopy of the cortical sensory representation of the fingers using a natural tactile stimulation of the glabrous skin. Multislice echoplanar imaging techniques were utilized to investigate blood oxygen level dependent (BOLD) signal changes as a measure of cortical activation. Repetitive sensory stimulation of the glabrous skin of digit II-III and digit IV-V resulted in a multifocal signal increase in a restricted area near the central sulcus in the contralateral hemisphere with a considerable overlap between the activated areas of digit II-III and digit IV-V. In addition, in all subjects tactile stimulation resulted in ipsilateral signal increase near the central sulcus, which was 15-22% of the contralateral effect. Stimulation of digit II-III caused significantly (P < 0.05) more activated voxels than digit IV-V in the contralateral hemisphere for both hands and for the left hand in the ipsilateral hemisphere. These findings suggest an ipsilateral activation of the primary somatosensory cortex during a natural tactile stimulation of the digits in humans.