SEF-MEG localization of somatosensory cortex as a method for presurgical assessment of functional brain area.

The surgical treatment of brain lesions adjacent to important functional areas is often limited. In the case of lesions in the proximity of the central region, modern imaging procedures cannot always render sufficient information on the exact relation to the motor cortex, especially if the cortex is distorted by the space occupying lesion. The localization of the central sulcus, with phase reversal and somatosensory evoked potentials, or direct motor stimulation, is now performed as a routine intraoperative measurement in many neurosurgical centres. A presurgical assessment of the topographic relation would facilitate the operative strategy of lesions neighbouring the central sulcus. With the advent of magnetoencephalography (MEG), intracranial electric sources can be localized with high temporal and spatial resolution. We used this method to determine whether the localization of somatosensory evoked fields (SEF) in the primary sensory cortex with the MEG is precise enough to allow its use in preoperative decision making. This method was previously introduced by Orrison (Orrison et al. 1992), Baumgartner (Baumgartner 1993) and Gallen (Gallen et al. 1993). In our study we used different stimulation and recording parameters and a self developed contour fit program. The SEFMEG results were compared to intraoperative phase reversal and direct motor stimulation.