title: Brain state-dependent functional hemispheric specialization in men but not in women.
abstract: Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or disconnected hemispheres, but is inconsistent in healthy populations. The reason for this paradox is unclear. We propose that functional hemispheric specialization in healthy participants depends upon functional brain states at stimulus arrival (FBS). Brain activity was recorded from 123 surface electrodes while 22 participants (11 women) performed lateralized lexical decisions (left hemisphere processing) on neutral and emotional (right hemisphere processing) words. We determined two classes of stable FBS, one with right anterior-left posterior orientations (RA-LP maps) and one with left anterior-right posterior orientations (LA-RP maps). Results show that functional hemispheric specialization is dependent upon the class of FBS and gender. Of those with LA-RP maps, only men showed a strong emotional word advantage (EWA) after left visual field (right hemisphere) presentation, but no EWA after right visual field (left hemisphere) presentation. Subsequent to all other brain states, there was an almost equal EWA after presentation to either visual field. Only about half of the FBS in men led to the pattern of functional hemispheric specialization. We suggest that 'split-brain' research may be marginally describable by a model, but only in exceptional situations, while in connected brains this functional hemispheric specialization is only one of many dynamic states.
authors.affiliation: The Functional Brain Mapping Laboratory of the Neurology Clinic, University Hospital Geneva, Geneva, Switzerland. Christine.Mohr@bristol.ac.uk
authors.forename: Christine
authors.initials: C
authors.lastname: Mohr
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Michel
authors.forename: Goran
authors.initials: G
authors.lastname: Lantz
authors.forename: Stephanie
authors.initials: S
authors.lastname: Ortigue
authors.forename: Isabelle
authors.initials: I
authors.lastname: Viaud-Delmon
authors.forename: Theodor
authors.initials: T
authors.lastname: Landis
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D016000:Cluster Analysis; D003657:Decision Making; D004569:Electroencephalography; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008606:Mental Processes / Q000502:physiology*; D015203:Reproducibility of Results; D012727:Sex Characteristics