Source Extraction Representing Thumb and Little Finger Cortical Networks and Intra-Hand-Area Evoked Synchrony

A novel cerebral source extraction method is proposed (Functional Source Separation, FSS) starting from extra-cephalic magnetoencephalographic (MEG) signals in humans, based on source functional reactivity to the external stimulation. Their activity is obtained all along the rest state and during processing of a simple separate sensory stimuli of thumb or little finger. This method provides cerebral sources describing thumb and little finger primary representations, as demonstrated by their higher responsiveness to the corresponding finger stimuli and their different positions consistent with the homuncular organization. A dynamical index describing intra-regional synchrony was introduced, which showed higher levels when stimulating the thumb with respect to little finger stimulation, selectively in the gamma band ([33, 44]Hz). This indicates that the stimulation of a functionally prevalent finger (thumb) activates a cortical network more synchronized in the gamma band than a nonprevalent one (little finger).