[Anatomical analysis of the sources of somatosensory evoked fields (SEFs) using 3D-MRI]

We have recorded short latency somatosensory evoked magnetic fields (SEFs) to left median nerve stimulation in three healthy subjects. The locations of the deduced dipole sources were projected onto the 3-Dimensional magnetic resonance imaging (3D-MRI) of the individual subjects providing an anatomical localization. We found that the deduced sources were located at the primary sensorimotor hand area on the posterior surface of the central sulcus, at an average depth of 26mm (11mm) from the scalp (brain surface). This technique that combined MEG with 3D-MRI was able to precisely determine source locations and analyze the relationships between dipole sources and brain structures. By using this technique, we can confirm functional anatomy of the brain noninvasively, and obtain much useful information preoperatively and during operation.