Anatomic localization of cerebral cortical function by magnetoencephalography combined with MR imaging and CT

Magnetoencephalography (MEG) monitors magnetic field amplitudes, which are time averages of evoked neuronal responses. This method can detect magnetic fields emanating from the brain and localize the neuronal source. The location of somatosensory neuronal sources for voluntary right thumb and right index finger flexions were determined in four normal volunteers by using a seven-sensor neuromagnetometer inside a magnetically shielded room. These neuronal sources were then identified on the individual's respective CT or MR scans, and correlation was accomplished by geometric calculations, direct cranial measurement, and surface marker identification. Specific functional magnetic fields were located over the appropriate sensory motor cortex; however, there was considerable variation in the exact site. Magnetoencephalography combined with CT and MR may improve localization of normal and abnormal neurologic function.