Organizzazione della corteccia somato-sensoriale secondaria: Studio con risonanza magnetica funzionale

-Aim of this study was to investigate the ability of fMRI to localise the secondary somatosensory (SII) areas in healthy humans following upper and lower limb sensory stimulation and possibly to reval its somatotopic organization. Nine volunteers (mean age 31 years) were involved in the study. They were briefly trained to lie down in a relaxed state, to avoid eye movements, and to maintain their limbs both in 'rest and 'stimulus' conditions. Stimulus consisted of electric pulses, 0.200 ms in duration and 1.9 s repetition rate. Mixed cutaneous and proprioceptive median and tibial nerve fibers were unilaterally stimulated. fMRI exam was performed by using a 1.5 Tesla equipment (Vision, Siemens). Twenty-two 3 mm thick slices, were acquired with no gap in 2 s by FID echo-planar imaging technique, paralellel to the plane bicommissural, from vertex to the superior temporal gyrus. In all subjects activated areas in the parietal lobes contralateral to the stimulated limb were found. They were consistent with the known homuncular organisation. A statistically significant increase of signal was localised in the slices passing through the upper bank of sylvian fissure, bilaterally. fMRI can detect the activation of the primary somatosensory cortex. The area of increased signal intensity detected in the upper bank of the sylvian fissure reflects the activation of SII.