Magnetoencephalographic presurgical investigation of time course and location of language processing in brain tumor patients

Magnetoencephalography (MEG) is a tool to investigate sources of brain activity with high spatial and temporal resolution. MEG also allows to evaluate higher cognitive functions like speech processing [3,7,13]. In this study we tried to investigate the time course of cortex activation of speech processing and to localize the underlying sources in a first step. Secondly we wanted to make these localizations available for clinical application. Functional mapping of speech eloquent areas is of high value for patients with brain tumors in the speech dominant hemisphere adjacent to the sensory (Wernicke) or the motor speech area (Broca). Neurosurgical treatment around eloquent brain areas bears a high risk of postoperative neurological deficits. To date the invasive Wada test [14] is the clinical standard to investigate speech lateralisation and memory functions. Functional mapping of eloquent areas is performed by intraoperative electrocorticography in local anesthesia at a few specialized neurosurgical centers only [11]. In recent years first results of noninvasive methods based on different physiologic mechanisms like MEG [3,8,13], fMRI [1,15,16] and PET [9,16] for mapping speech relevant areas and determining the speech dominant hemisphere were presented. Our aim was to preoperatively identify the speech dominant hemisphere and localize the speech relevant brain areas noninvasively by means of MEG. Similar to surgery of tumors around the sensorimotor cortex by functional neuronavigation [2,5] as performed in our department we wanted to make the MEG localizations intraoperatively available for the surgeon by displaying the Broca or Wernicke area in the operation microscope.