title: Language and its right-hemispheric distribution in healthy brains: an investigation by repetitive transcranial magnetic stimulation.
abstract: OBJECTIVE
  Repetitive navigated transcranial magnetic stimulation (rTMS) is increasingly used for preoperative cortical language mapping. Unlike direct cortical stimulation (DCS), and due to its non-invasive character, this technique can provide a map of the distribution of human language in the healthy brain as well as a dysfunctional brain. Although functional magnetic resonance imaging (fMRI) studies have reported interhemispheric functional connectivity between language structures, the way in which the right hemisphere helps bring about language function remains only partially investigated. The present study therefore uses rTMS as a virtual lesion model to investigate the right hemisphere's contribution to language processing in the healthy human brain.
  
  
  METHODS
  Fifty healthy right-handed volunteers (25 males, 25 females, mean age 25.9 ± 5.4 years) underwent language mapping of the right hemisphere by rTMS combined with an object naming task. All errors induced by rTMS were categorized into six different error groups (no-response error, hesitation, performance error, neologism, semantic error, and phonological error). Afterwards, the error rates for each category were calculated and visualized through the results' being projected into the cortical parcellation system (CPS). To reveal CPS regions having similar functional properties, an additional principal component analysis (PCA) was performed.
  
  
  RESULTS
  rTMS induced 1485 naming errors out of the 9839 stimulation trains (error rate 15.1%). These errors were located mainly in the right hemisphere's homologues of the left hemisphere's visually cued overt speech area (middle superior temporal gyrus: mSTG) and in the sound-to-articulation dorsal pathway consisting of opercular inferior frontal gyrus (opIFG) and anterior and posterior supramarginal gyrus (aSMG, pSMG) in both male and female brains. In addition, rTMS caused many errors in the global language comprehension area in female brains (right posterior superior temporal gyrus: pSTG), in speech motor areas in the middle and ventral precentral and postcentral gyri (mPrG, vPrG, mPoG, vPoG), and in executive-function areas in the middle and posterior middle frontal gyri (mFMG, pMFG).
  
  
  CONCLUSIONS
  For the first time, the present study provides data on the right hemisphere's cortical regions causally related to single word production function (right opIFG, aSMG, pSMG, mSTG), and selectively in female brains (right pSTG), from a large sample of 50 healthy adult brains in a virtual-lesion design. Moreover, speech-motor control regions (right mPrG, vPrG, mPoG, vPoG) and cortical regions supporting language task performance (mMFG, pMFG) in the language-non-dominant right hemisphere are described.
authors.affiliation: Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany. Electronic address: Nico.Sollmann@lrz.tum.de.
authors.forename: Nico
authors.initials: N
authors.lastname: Sollmann
authors.affiliation: Faculty of Linguistics, Philology, & Phonetics, University of Oxford, Walton Street, Oxford OX1 2HG, UK. Electronic address: noriko.tanigawa@ling-phil.ox.ac.uk.
authors.forename: Noriko
authors.initials: N
authors.lastname: Tanigawa
authors.affiliation: Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany. Electronic address: Florian.Ringel@lrz.tum.de.
authors.forename: Florian
authors.initials: F
authors.lastname: Ringel
authors.affiliation: Section of Neuroradiology, Department of Radiology, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany. Electronic address: Claus.Zimmer@tum.de.
authors.forename: Claus
authors.initials: C
authors.lastname: Zimmer
authors.affiliation: Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany. Electronic address: Bernhard.Meyer@lrz.tum.de.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Meyer
authors.affiliation: Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany. Electronic address: Sandro.Krieg@lrz.tum.de.
authors.forename: Sandro M
authors.initials: SM
authors.lastname: Krieg
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D054022:Cerebrum / Q000502:physiology*; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D011446:Prospective Studies; D050781:Transcranial Magnetic Stimulation / Q000379:methods
keywords: Cortical mapping; Language; Navigated brain stimulation; Object naming; Transcranial magnetic stimulation