FINGERTIP REPRESENTATION IN THE HUMAN SOMATOSENSORY CORTEX - AN FMRI STUDY

Eight right-handed adult humans underwent functional magnetic resonanc e imaging (fMRI) of their brain while a vibratory stimulus was applied to an individual digit tip (digit 1, 2, or 5) on the right hand. Mult islice echoplanar imaging techniques were utilized during digit stimul ation to investigate the organization of the human primary somatosenso ry (SI) cortex, cortical regions located on the upper bank of the Sylv ian fissure (SII region), insula, and posterior parietal cortices. The t test and cluster size analyses were performed to produce cortical a ctivation maps, which exhibited significant regions of interest (ROIs) in all four cortical regions investigated. The frequency of significa nt ROIs was much higher in SI and the SII region than in the insula an d posterior parietal region. Multiple digit representations were obser ved in the primary somatosensory cortex, corresponding to the four ana tomic subdivisions of this cortex (areas 3a, 3b, 1, and 2), suggesting that the organization of the human somatosensory cortex resembles tha t described in other primates. Overall, there was no simple medial to lateral somatotopic representation in individual subject activity maps . However, the spatial distance between digit 1 and digit 5 cortical r epresentations was the greatest in both SI and the SII region within t he group. Statistical analyses of multiple activity parameters showed significant differences between cortical regions and between dig-its, indicating that vibrotactile activations of the cortex are dependent o n both the stimulated digit and cortical region investigated. (C) 1998 Academic Press.