SOMATOSENSORY-EVOKED MAGNETIC-FIELDS FOLLOWING PASSIVE FINGER MOVEMENT

The somatosensory evoked magnetic field (SEF) following passive finger movement and electrical stimulation of finger was studied in 10 norma l subjects. Four main components were identified in SEFs recorded at t he hemisphere contralateral to the moved finger: 1M(P), 2M(P), 3M(P) a nd 4M(P). The 1M(P) was clearly identified only in three subjects and was smaller than other components. The equivalent current dipoles (ECD s) of 1M(P) were located around the finger area of the primary sensori motor cortex and oriented either posteriorly or anteriorly. We specula te that it was generated in areas 3a or 2 of the primary sensory corte x. The 2M(P) and 3M(P) were usually combined as one large deflection w ith two peaks. Because the ECDs of 2M(P) and 3M(P) were located around the finger area of the sensorimotor cortex and both oriented posterio rly, they were considered to be generated in area 4 and/or 3b, and the ir activities have temporal overlapping. The 4M(P) has large inter-ind ividual difference in terms of amplitude and latency. The ECD of 4M(P) was also located around the finger area of the primary sensorimotor c ortex, and oriented anteriorly. The 4M(PI), the main component recorde d from the hemisphere ipsilateral to the moved finger, was located in the upper bank of the sylvian fissure, probably the second sensory cor tex (SII). Five components, 1M(E), 2M(E), 3M(E), 4M(E) and 4M(EI), cor responding to 1M(P), 2M(P), 3M(P), 4M(P) and 4M(PI), were identified f ollowing electrical stimulation of the same finger. However, SEFs foll owing passive movement were clearly different from SEFs following elec trical stimulation, in terms of waveforms and source locations, probab ly due to differences of ascending fibers and receptive fields. (C) 19 97 Elsevier Science B.V.