title: Rapid and minimum invasive functional brain mapping by real-time visualization of high gamma activity during awake craniotomy.
abstract: BACKGROUND
  Electrocortical stimulation (ECS) is the gold standard for functional brain mapping during an awake craniotomy. The critical issue is to set aside enough time to identify eloquent cortices by ECS. High gamma activity (HGA) ranging between 80 and 120 Hz on electrocorticogram is assumed to reflect localized cortical processing. In this report, we used real-time HGA mapping and functional neuronavigation integrated with functional magnetic resonance imaging (fMRI) for rapid and reliable identification of motor and language functions.
  
  
  METHODS
  Four patients with intra-axial tumors in their dominant hemisphere underwent preoperative fMRI and lesion resection with an awake craniotomy. All patients showed significant fMRI activation evoked by motor and language tasks. During the craniotomy, we recorded electrocorticogram activity by placing subdural grids directly on the exposed brain surface.
  
  
  RESULTS
  Each patient performed motor and language tasks and demonstrated real-time HGA dynamics in hand motor areas and parts of the inferior frontal gyrus. Sensitivity and specificity of HGA mapping were 100% compared with ECS mapping in the frontal lobe, which suggested HGA mapping precisely indicated eloquent cortices. We found different HGA dynamics of language tasks in frontal and temporal regions. Specificities of the motor and language-fMRI did not reach 85%. The results of HGA mapping was mostly consistent with those of ECS mapping, although fMRI tended to overestimate functional areas.
  
  
  CONCLUSIONS
  This novel technique enables rapid and accurate identification of motor and frontal language areas. Furthermore, real-time HGA mapping sheds light on underlying physiological mechanisms related to human brain functions.
authors.affiliation: Department of Neurosurgery, School of Medicine, Asahikawa Medical University, Asahikawa, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ogawa
authors.affiliation: Department of Neurosurgery, School of Medicine, Asahikawa Medical University, Asahikawa, Japan. Electronic address: kamady-k@umin.ac.jp.
authors.forename: Kyousuke
authors.initials: K
authors.lastname: Kamada
authors.affiliation: Guger Technologies OG, Graz, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Kapeller
authors.affiliation: Department of Neurosurgery, School of Medicine, Asahikawa Medical University, Asahikawa, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Hiroshima
authors.affiliation: Guger Technologies OG, Graz, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Prueckl
authors.affiliation: Guger Technologies OG, Graz, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Guger
mesh_terms: D000328:Adult; D000368:Aged; D001931:Brain Mapping / Q000379:methods*; D001932:Brain Neoplasms / Q000601:surgery*; D003399:Craniotomy / Q000379:methods*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods; D005625:Frontal Lobe / Q000502:physiology / Q000601:surgery; D005909:Glioblastoma / Q000601:surgery*; D006801:Humans; D007431:Intraoperative Complications / Q000517:prevention & control; D007802:Language; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D010296:Parietal Lobe / Q000502:physiology / Q000601:surgery; D014851:Wakefulness
keywords: Awake craniotomy; Electrocorticogram; High gamma activity; Real-time mapping