Discrimination of multiple sources in the somatosensory area of human finger based on 3-D SEF measurement

To discriminate multiple sources of human hand somatosensory cortex we recorded somatosensory evoked field after stimulation of three fingers (the thumb, fourth finger, and little finger), respectively. Time-frequency analysis (wavelet transforms, WT) was applied to the SEF data to examine the frequency component of each SEF data. Dominant power spectrum to the thumb (median nerve) stimulation appeared at higher frequency range than that of the little finger (ulnar nerve) stimulation (thumb: 15–20 Hz, little finger: 10–15 Hz). The frequency of dominant power spectrum to the fourth finger stimulation existed between that of the thumb and little finger stimulation. From the result of the coherence by the SEF data between the fourth finger and the other finger, band-pass filtering for the fourth finger was done with different frequency ranges (13–15 Hz: little finger and 16–18 Hz: the thumb). Source localization was done with these SEF data. It was confirmed that the proposed method, combining time-frequency analysis with the inverse problem of MEG (magnetoencephalogram), is useful for discriminating multiple sources of the SEF elicited by two nerve activities in the fourth finger overlapping in time.