title: Magnetoencephalography in neurosurgery.
abstract: OBJECTIVE
  To present applications of magnetoencephalography (MEG) in studies of neurosurgical patients.
  
  
  METHODS
  MEG maps magnetic fields generated by electric currents in the brain, and allows the localization of brain areas producing evoked sensory responses and spontaneous electromagnetic activity. The identified sources can be integrated with other imaging modalities, e.g., with magnetic resonance imaging scans of individual patients with brain tumors or intractable epilepsy, or with other types of brain imaging data.
  
  
  RESULTS
  MEG measurements using modern whole-scalp instruments assist in tailoring individual therapies for neurosurgical patients by producing maps of functionally irretrievable cortical areas and by identifying cortical sources of interictal and ictal epileptiform activity. The excellent time resolution of MEG enables tracking of complex spaciotemporal source patterns, helping, for example, with the separation of the epileptic pacemaker from propagated activity. The combination of noninvasive mapping of subcortical pathways by magnetic resonance imaging diffusion tensor imaging with MEG source localization will, in the near future, provide even more accurate navigational tools for preoperative planning. Other possible future applications of MEG include the noninvasive estimation of language lateralization and the follow-up of brain plasticity elicited by central or peripheral neural lesions or during the treatment of chronic pain.
  
  
  CONCLUSIONS
  MEG is a mature technique suitable for producing preoperative "road maps" of eloquent cortical areas and for localizing epileptiform activity.
authors.affiliation: BioMag Laboratory, Engineering Centre, Helsinki University Central Hospital, Helsinki, Finland. jyrki.makela@hus.fi
authors.forename: Jyrki P
authors.initials: JP
authors.lastname: Mäkelä
authors.forename: Nina
authors.initials: N
authors.lastname: Forss
authors.forename: Juha
authors.initials: J
authors.lastname: Jääskeläinen
authors.forename: Erika
authors.initials: E
authors.lastname: Kirveskari
authors.forename: Antti
authors.initials: A
authors.lastname: Korvenoja
authors.forename: Ritva
authors.initials: R
authors.lastname: Paetau
mesh_terms: D001927:Brain Diseases / Q000175:diagnosis / Q000628:therapy; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D019635:Neurosurgical Procedures / Q000379:methods*; D011300:Preoperative Care / Q000379:methods