Combination of magnetoencephalography (MEG) and functional magnetic resonance imaging (FMRI) for neurosurgical mapping of the sensory and motor cortices

Magnetoencephalography (MEG) and functional magnetic resonance imaging (FMRI) were applied to brain mapping in normal volunteers and three patients with tumors. Somatosensory evoked fields (SEFs) due to median, ulnar and posterior tibial nerve stimulation were measured using a whole head MEG system. FMRI used an echo planner imaging method during hand, toe and lip movement. Estimated SEF dipoles and activated FMRI regions were superimposed on anatomical MRI. The central sulcus was identified by source localization of the SEFs in all subjects. Functional abnormality could be detected as reduced amplitude or latency delay of the SEF peaks. FMRI indicated multiple and extended regions of activation, such as primary motor, primary sensory and supplementary motor cortices. The highest signal activation was usually found in the contralateral primary sensory/motor cortices. However, the primary motor and sensory cortices were not activated due the effect of the lesion in one patient. The highest activation was found far posterior to the central sulcus due to a large venous inflow effect in another patient. The combination of MEG and FMRI can avoid any misinterpretation due to use of only one method of functional brain mapping, especially in patients with brain lesions