title: Are there excitability changes in the hand motor cortex during speech in left-handed subjects?
abstract: Hemispheric dominance was investigated in left-handed subjects using single transcranial magnetic stimulation to assess the possible effect of forced change in the dominant hand. Single transcranial magnetic stimuli were delivered randomly over the hand area of the left or right motor cortex of 8 Japanese self-declared left-handed adult volunteers. Electromyographic responses were recorded in the relaxed first dorsal interosseous muscle while the subjects read aloud. Laterality quotient calculated by the Edinburgh Inventory ranged from -100 to -5.26 and laterality index calculated from motor evoked potentials ranged from -86.2 to 38.8. There was no significant correlation between laterality quotient and laterality index. Mean data values across all 8 subjects indicated significant increases only in the left hand. Our ratio analysis of facilitation of the hand motor potentials showed that 2 each of the 8 self-declared left-handers were right- and left-hand dominant and the other 4 were bilateral-hand dominant. Speech dominancy was localized primarily in the right cerebral hemisphere in left-handed subjects, but some individuals exhibited bilateral or left dominance, possibly attributable to the forced change of hand preference for writing in childhood. Our findings suggest changes in the connections between the speech and hand motor areas.
authors.affiliation: Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima. hiroshitok@nag.bbiq.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tokimura
authors.forename: Yoshika
authors.initials: Y
authors.lastname: Tokimura
authors.forename: Kazunori
authors.initials: K
authors.lastname: Arita
mesh_terms: D000328:Adult; D004292:Dominance, Cerebral / Q000502:physiology*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009044:Motor Cortex / Q000502:physiology*; D013060:Speech / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult