• C Civardi, A Cavalli, P Naldi, C Varrasi, and R Cantello.
• Department of Neurology, Amedeo Avogadro University School of Medicine, Ospedale Maggiore della Carità, C.so Mazzini 18, 28100, Novara, Italy.
• Clin Neurophysiol. 2000 Apr 1;111(4):624-9.

ObjectiveTo evaluate possible functional asymmetries of the motor cortex on the hand-dominant versus the non-dominant hemisphere.MethodsWe assessed the handedness of 15 consenting volunteers using the Edinburgh Inventory. They were divided in two groups: 9 right-handers and 6 left-handers. We used single- and paired-transcranial magnetic stimulation (TMS) to measure the relaxed and active motor threshold and the ipsilateral cortico-cortical inhibition and facilitation curve for both hand motor areas. We looked for hemispheric asymmetries of variables related to the side of stimulation (dominant versus non-dominant) and to handedness.ResultsWe found no significant intra- or intergroup hemispheric asymmetry for the relaxed and active thresholds. Among the right-handers, the cortico-cortical inhibition and facilitation curve showed an increased amount of facilitation in the dominant as compared with the non-dominant hand area. No such changes were seen among the left-handers. Both the dominant and the non-dominant hand areas of the right-handers showed more inhibition and less facilitation on the cortico-cortical inhibition and facilitation curve than the corresponding areas of left-handers.ConclusionIn the right-handers, paired TMS studies showed a functional asymmetry of the motor cortex between the dominant and the non-dominant hand. The left-handers did not show this lateralization. Under TMS investigation their motor cortex function appeared different from that of right-handers.

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