title: Handedness is mainly associated with an asymmetry of corticospinal excitability and not of transcallosal inhibition.
abstract: OBJECTIVE
  The study aims to compare transcallosal inhibition (TI), as assessed by the paired-pulse transcranial magnetic stimulation (TMS) technique, in a sample of right-handed subjects (RH) and left-handed subjects (LH). Motor thresholds (MTs) and motor evoked potential (MEP) amplitudes were also measured in the two groups, as an index of corticospinal activity.
  
  
  METHODS
  Thirty-two normal subjects (16 RH and 16 LH) were recorded with a paired-pulse TMS paradigm (intensity of both pulses=120% of MT). The inter-stimulus intervals (ISIs) were 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 ms for both motor cortices, and MEP responses were recorded from the abductor digiti minimi muscles.
  
  
  RESULTS
  Both groups showed a clear TI centred around the 12 ms ISI, but no difference was found as a function of handedness or of hemisphere. On the other hand, the two groups differed in terms of corticospinal activity, since the hand motor dominant hemisphere had lower MTs than the non-dominant one in LH, and larger MEP amplitudes for the right hand were found in RH.
  
  
  CONCLUSIONS
  Results point to a functional asymmetry of the motor cortex on the hand-dominant versus the non-dominant hemisphere, while handedness does not seem associated with functional differences in callosal inhibition, as measured by the inter-hemispheric paired-pulse TMS technique.
authors.affiliation: Dipartimento di Psicologia, Università di Roma La Sapienza, Via dei Marsi 78, 00185 Rome, Italy. luigi.degennaro@uniroma1.it
authors.forename: Luigi
authors.initials: L
authors.lastname: De Gennaro
authors.forename: Riccardo
authors.initials: R
authors.lastname: Cristiani
authors.forename: Mario
authors.initials: M
authors.lastname: Bertini
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Curcio
authors.forename: Michele
authors.initials: M
authors.lastname: Ferrara
authors.forename: Fabiana
authors.initials: F
authors.lastname: Fratello
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Romei
authors.forename: Paolo M
authors.initials: PM
authors.lastname: Rossini
mesh_terms: D000328:Adult; D003337:Corpus Callosum / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008280:Magnetics; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*