Somatosensory cortex activation during electrical stimulation of projected finger map on the stump skin of forearm amputee

The objective of this study was to test the hypothesis that electrical stimulation of projected finger map (PFM) in the stump skin of forearm amputees activates concurrently the corresponding finger areas in the primary somatosensory cortex (S1). The technique of magnetoencephalo-graphy (MEG) was used to detect S1 activities, while electrical stimulation pulses or trains were delivered to three sites: (1) the thumb and little finger areas of the PFM on the stump skin of an amputee subject; (2) the thumb and little finger of the contralateral hand of the subject; and (3) the contralateral forearm skin areas matching the PFM in the amputated stump. Result indicated that at single pulse stimulus (1Hz) to the thumb and little fingers in the PFM and contralateral hand, symmetric areas in S1 corresponding to the thumb (more lateral) and little finger (lateral) in both sides could be identified. With stimulation train (50Hz and duty cycle of 50%) to the thumb and little finger in the PFM and contralateral hand, the subject experienced pressure sensations similarly at both sites, and the same symmetric areas of the thumb (more lateral) and little finger (lateral) in S1 were activated. With stimulation at the third site, the activation area in S1 was located towards more medial (elbow) segment. MEG results indicated that PFM stimulation evoked S1 activation consistent with homunculus organization. This may imply that the thumb and little finger areas in the PFM on the stump skin are connected neuroanatomically to the thumb and little finger areas in S1 before amputation.